Switch Yard Erection(2)

FOR INTERNAL CIRCULATION ONLY

user’s manual of Construction (part two)

Sub-Stations Volume-3 Switchyard Erection

Construction Management

Power Grid Corporation of India Limited (A Government of India Enterprise) DOCUMENT CODE NO. : CM/SS/SW. ERN/99

SEPT, 1999

CONTENTS CHAPTER ONE ELECTRICAL SUBSTATION PAGE NO.

1.O

INTRODUCTION

1

1.1

FUNCTIONS OF A SUB-STATION

2

1.2

VOLTAGE LEVELS IN AC SUBSTATIONS AND HVDC SUBSTATIONS

3

1.3

FORMS OF SUBSTATIONS

4

1.4

TYPES OF SUBSTATIONS

6

1.5

ESSENTIAL FEATURES OF A SUBSTATION

7

1.5.1

SPECIAL FEATURES

1.6

SITE SELECTION

12 13

ANNEXURE - I FORMAT FOR COMPARATIVE STATEMENT OF SITES FOR SUBSTATION 1.6.1

LAND ACQUISITION

1.6.2

PROVISIONS UNDER THE LAND

14 16

ACQUISITION ACT, 1894 FOR SUB-STATIONS 1.6.3

16

LAND ACQUISITION ACT,1894 AS AMENDED IN 1984

17

ANNEXURE - II ACTIVITY CHART(TIME FRAME)

18

1.7

SUBSTATION PARTS AND EQUIPMENT

1.8

FUNCTIONS OF SUB-STATION EQUIPMENTS & ASSOCIATED SYSTEMS

1.9

SUBSTATIN LAYOUTS, BUSBAR SCHEMES

1.10

CONSTRUCTION/ERECTION DRAWINGS

CHAPTER TWO SWITCHYARD CIVIL WORKS 2.0

INTRODUCTION

2.1

SOIL INVESTIGATION

2.2

LEVELLING

2.3

FOUNDATIONS

2.4

FOUNDATIONS

FOR

TRANSFORMER

&

SHUNT

REACTORS 2.5

CABLE TRENCHES IN SWITCHYARD

2.6

CABLE TRENCH COVER SLABS

2.7

ANTI-WEED TREATMENT, MICRO LEVELLING’ GRAVEL FILLING & METAL SPREADING

2.7.1

ANTI-WEED TREATMENT

2.7.2

MICRO LEVELLING

2.7.3

METAL SPREADING IN SWITCHYARD

2.8

DO’S, DON’T’S & SPECIAL PRECAUTIONS

2.9

CHECK FORMAT

CHAPTER THREE SWITCHYARD EARTHING 3.0 3.1

INTRODUCTION FUNCTIONAL REQUIREMENTS OF EARTHING SYSTEM

3.2

EARTHNG SYSTEM IN SWITCHYARD

3.3

STEP AND TOUCH POTENTIAL

3.3.1

STEP POTENTIAL

3.3.2 3.4

TOUCH POTENTIAL SOIL RESISTIVITY

3.5

EARTHING MATERIAL

3.6

EARTHING CONDUCTOR LAYOUT

3.7

EQUIPMENT AND STRUCTURE EARTHING

45

IN SUBSTATION

45

3.8

JOINTING

48

3.9

MEASUREMENT OF EARTH RESISTANCE

49

3.10

DO'S DON'TS AND SPECIAL PRECAUTIONS

3.11

CHECK FORMAT

50

CHAPTER FOUR SWITCHYARD STRUCTURES

4.0

INTRODUCTION

4.1

STRUCTURE WORKS IN SUBSTATION

54

SWITCHYARD

54

4.2

RECEIPT OF MATERIAL & INSPECTION

54

4.3

STORAGE

55

4.4

ERECTION

55

4.4.1

ERECTION OF GANTRY & LATTICE STRUCTURES 55

4.4.2

ERECTION OF PIPE STRUCTURE

57

4.3

LIGHTNING MASTS

57

4.4

DO'S, DONT'S AND SPECIAL PRECAUTIONS

58

4.5

CHECK FORMAT

60

CHAPTER FIVE BUS POST INSULATORS & BUS BARS

5.0

INTRODUCTION

62

5.1

STEPS IN BUSBAR DESIGN

62

5.2

FORMS OF BUSBARS

63

5.2.1

ACSR

63

5.2.2

ALUMINIUM

63

5.3

CONFIGURATION OF BUSBARS IN OUTDOOR SUBSTATION

5.4

64

RECEIPT AND INSPECTION OF MATERIAL AT SITE

64

5.5

BUS POST INSULATORS

65

5.5.1

TECHNICAL PARAMETERS OF BUS POST INSULATORS

66

5.6

ERECTION OF ALUMINIUM BUS BAR

5.6.1

BENDING PROCEDURE OF ALUMINIUM TUBE

67

DURING ERECTION

68

5.6.2

WELDING OF ALUMINIUM TUBE

68

5.7

WELDING PROCEDURE AND WELDER'S QUALIFICATIONS

69

5.8

DO'S, DONT'S AND SPECIAL PRECAUTIONS

70

5.9

CHECK FORMAT

71

CHAPTER SIX STRINGING IN SWITCHYARD

6.0

INTRODUCTION

78

6.1

PRE-STRINGING CHECKS

78

6.2

STRINGING

79

6.3

T&P AND MATERIALS USED FOR STRINGING

79

6.4

DO’S DONT’S AND SPECIAL PRECAUTIONS

81

6.5

CHECK FORMAT

84

CHAPTER SEVEN SURGE ARRESTER

7.0

INTRODUCTION

7.1

CONVENTIONAL GAPPED LIGHTNING ARRESTER

86

(VALVE TYPE ARRESTER)

86

7.2

METAL OXIDE LIGHTNING ARRESTERS

87

7.3

PACKING, TRANSPORT, HANDLING AND STORAGE

88

7.4

INSTALLATION

89

7.5

INSTALLATION OF SINGLE UNIT ARRESTER

89

7.6

INSTALLATION OF MULTI-STACK ARRESTER

89

7.7

DO'S, DONT'S & SPECIAL PRECAUTIONS

91

7.8

CHECK FORMAT

92

CHAPTER EIGHT ISOLATORS 8.0

INTRODUCTION

94

8.1

CONSTRUCTION FEATURES

94

8.1.1

SUPPORT STRUCTURE

95

8.1.2

BASE ASSEMBLY

95

8.1.3

INSULATOR ASSEMBLY

95

8.1.4

MALE AND FEMALE CONTACTS ASSEMBLY

96

8.2.

OPERATING MECHANISM

96

8.2.1

GEARED OPERATING MECHANISM

96

8.2.2

MANUAL OPERATING MECHANISM

96

8.2.3

EARTH SWITCH ASSEMBLY

97

8.3

RECEIPT, HANDLING AND STORAGE

97

8.4

ERECTION/INSTALLATIONS

97

8.4.1

STRUCTURES

97

8.4.2

BASE ASSEMBLY

98

8.4.3

INSULATORS

98

8.4.4

CONTACTS ASSEMBLY (MALE AND FEMALE ASSEMBLY)

99

8.4.5

CONNECTING DISCONNECTOR

100

8.4.6

CONTROLS FOR ELECTRICAL OPERATING EQUIPMENT

101

8.5

CLOSING OPERATION OF ISOLATOR

101

8.6

TANDEM PIPE ASSEMBLY

102

8.7

EARTH SWITCH ASSEMBLY

102

8.8

DO'S, DONT'S AND SPECIAL PRECAUTIONS

104

8.8.1

ADJUSTMENT IN DRIVE/ASSEMBLY ERECTION

8.9

CHECK FORMAT

104 107

CHAPTER NINE CURRENT TRANSFORMER 9.0

INTRODUCTION

109

9.1

CONSTRUCTION FEATURES

109

9.2

HERMETIC SEALING

111

9.3

TRANSPORTATION, UNPACKING & INSPECTION

111

9.4

INSTALLATION/ERECTION

112

9.5

DO'S DONT'S & SPECIAL PRECAUTIONS

114

9.6

CHECK FORMAT

115

CHAPTER TEN CAPACITIVE VOLTAGE TRANSFORMER 10.0

INTRODUCTION

117

10.1

DESCRIPTION & OPERATING PRINCIPLE

117

10.2

PACKING AND TRANSPORTATION

119

10.3

RECEIVING

120

10.4

UNLOADING

120

10.5

STORAGE

121

10.6

INSTALLATION

122

10.7

CONNECTION

122

10.8

DO'S, DONT'S AND SPECIAL PRECAUTIONS

125

10.8.1

INSPECTION BEFORE MOUNTING

125

10.8.2

DEFECT/DAMAGE

126

10.8.3

MINOR IRREGULARITIES

127

10.8.4

ERECTION

127

10.9

CHECK FORMAT

128

CHAPTER ELEVEN POWER LINE CARRIER COMMUNICATION 11.0

INTRODUCTION

129

11.1

PLC SYSTEM

129

11.2

COUPLING EQUIPMENT

129

11.3

COUPLING EQUIPMENT DESCRIPTION

130

11.4

CONSTRUCTION FEATURES

130

11.5

DATA TRANSMISSION

131

11.6

TELEPROTECTION

131

11.7

CARRIER PANEL

131

11.8

EARTHING

131

11.9

ERECTION OF PLCC AND ASSOCIATED EQUIPMENT

132

11.9.1

OUTDOOR EQUIPMENTS

132

11.9.2

INDOOR EQUIPMENTS

134

11.10

CONNECTION OF HF CO-AXIAL CABLE

11.11

INSTALLATION OF EQUIPMENT AS PER

136

PLANNED SYSTEM 11.12

137

DEFECTIVE MODULES AND FAULT RECTIFICATION AT SITE

137

11.13

DO'S, DON'TS AND SPECIAL PRECAUTIONS

139

11.14

CHECK FORMAT

141

CHAPTER TWELVE CABLES 12.0

INTRODUCTION

143

12.1

RECEIPT, INSPECTION AND STORAGE

144

12.2

CABLE LAYING IN SWITCHYARD

144

12.2.1

CABLE LAYING IN UNDERGROUND (BURIE TRENCHES)

145

12.2.2

CABLE LAYING IN CABLE TRAYS

145

12.3

CABLE TERMINATION

146

12.4

DO'S DON'TS AND SPECIAL PRECAUTIONS

12.5

CHECK FORMAT

148 152

CHAPTER THIRTEEN CONTROL AND RELAY PANELS 13.0

INTRODUCTION

154

13.1

CONSTRUCTION FEATURES

155

13.2

SIMPLEX PANEL

156

13.3

DUPLEX PANEL

156

13.4

RECEIPT AND STORAGE AT SITE

156

13.5

ERECTION OF PANELS

157

13.6

MOUNTING ON PANELS

158

13.7

PANEL INTERNAL WIRING AND EQUIPMENTS IN PANELS

158

13.8

PROVIDING TERMINAL BLOCKS

159

13.9

NAME PLATES AND MARKINGS

160

13.10

PANELS ACCESSORIES

160

13.11

EARTHING

161

13.12

DO'S DON'TS AND SPECIAL PRECAUTIONS

13.13

CHECK FORMAT

162

Chapter-1 ELECTRICAL SUBSTATION

________________________________________________________________________________ _ CHAPTER ONE ________________________________________________________________________________ _

ELECTRICAL SUBSTATION Back to contents page

1.0

Introduction Back to contents page

An electrical Network comprises of the following systems: 

Generating Stations



Transmission Systems



Receiving Stations



Distribution Systems



Load Points

In all these systems, the power flow of electrical energy takes place through Electrical Substations. An Electrical Substation is an assemblage of electrical components including busbars, switchgear, power transformers, auxiliaries, etc.

Basically an electrical substation

consists of a number of incoming circuits and outgoing circuits connected to common busbar system. Busbars are conducting bars to which a number of incoming or outgoing circuits are connected. Each circuit has certain electrical components such as circuit-breakers, isolators, earthing switches, current transformers, voltage transformers, etc. These components are connected in a definite sequence such that a circuit can be switched off/on during normal operation by manual/remote command and also automatically during abnormal conditions such as short-circuits. A substation receives electrical power from generating station via incoming transmission lines and delivers electrical power via the outgoing transmission lines. Substations are integral parts of a power system and form important links between the generating stations, transmission and distribution systems and the load points.

1.1

Functions of a sub-station: Back to contents page

An electricity supply undertaking generally aims at the following: 

Supply of required electrical power to all the consumers continuously at all times.



Maximum possible coverage of the supply network over the given geographical area.



Maximum security of supply.



Shortest possible fault duration.



Optimum efficiency of plants and the network.



Supply of electrical power within targeted frequency limits.



Supply of electrical power within specified voltage limits.



Supply of electrical energy to the consumers at the lowest cost.

As a result of these objectives, there are various tasks which are closely associated with the generation, transmission, distribution and utilisation of the electrical energy. These tasks are performed by various, manual, semi-automatic and fully automatic devices located in generating stations and substations. The tasks associated with a major substation in the transmission system include the following: 

Controlling the exchange of energy



Protection of transmission system



Ensuring steady state and transient stability



Load

shedding

and

prevention

of

loss

of

synchronism.

Maintaining the system frequency within targeted limits 

Voltage

control,

reducing

the

reactive

power

flow

by

compensation of reactive power, tap-changing. 

Securing the supply by providing adequate line capacity and facility for changing the transmission paths.



Data transmission via power line carrier for the purpose of network monitoring, control and protection.



Determining the energy transfer through transmission lines and tie-lines.



Fault analysis and pin-pointing the cause and subsequent improvements.



Securing supply by feeding the network at various points.

All these tasks are performed by the team work of load-control centre and control rooms of substations. The substations perform several important tasks and are integral part of the power system. 1.2

Voltage Levels in AC Substations and HVDC Substations Back to contents page

A substation receives power via the incoming transmission lines and delivers power via the outgoing lines.

The substation may have step-up

transformers or step-down transformers. Generally the switchyards at sending-end of lines have step-up transformers and switchyards at receiving-end have step-down transformers. The rated voltage level refers to nominal voltage of 3 phase AC system and is expressed as r.m.s. value between phases. An AC substation has generally 2 or 3 main voltage levels. The long distance transmission is generally at extra high voltages such as 132 kV, 220 kV, 400 kV AC The subtransmission is at medium high voltage such as 33 kV, 11 kV AC. In a generating station, the generator is directly connected to step-up transformer and secondary of the step-up transformer is connected to outdoor EHV switchyard. The switchyard in a generating station comprises generator transformer, unit auxiliary transformer and several out-going lines. In addition to the main EHV switchyard, a generating station has indoor auxiliary switchgear at two or three voltages such as 11 kV, 400 Volts. The factory substations receive power at distribution voltage such as 11 kV and step it down to 440 volts AC. Larger factories receive power at 132 kV and have internal distribution at 440 volts AC. The choice of incoming and outgoing voltages of substations is decided by the rated voltages and rated power of corresponding lines. Long distance and high power transmission lines are at higher voltages. The nominal voltages are selected from the standard values of rated voltages specified in Indian Standards or relevant national standard. The standards also specify the following reference values for each voltage level.



Nominal voltage e.g. 220 kV, 400 kV



Highest system voltage, e.g. 245 kV, 420 kV



Lowest system voltage, e.g. 200 kV, 185 kV.

Table 1: Reference Values of Nominal Voltages in AC and HVDC Substations AC Substation 765 kV, 400 kV, 220 kV, 132 kV, 66 kV, 33 kV, 11 kV HVDC Substation +400 Kv, +500 kV, +600 kV Station Auxiliaries Aux. AC Supply : 33 kV, 11 kV 400 V, 3 ph., phase to phase 230 V AC single phase Aux. LVDC : 220 V, 110 V, 48 V DC 1.3

Forms of Substations Back to contents page

For voltage upto 11 kV, the sub-stations are either in the form of indoor metal clad draw-out type Switchgear or Outdoor Kiosk. In indoor metal clad switchgear, the required number of factory assembled units are taken to site and placed in a row.

SF6 Gas Insulated Switchgear has

been introduced for medium to high voltages such as 11 kV, 33 kV & upto 400 kV level. For voltages of 33 kV and above, outdoor substations are generally preferred. In outdoor substations, the various equipments are installed in open. The indoor and outdoor substations have similar components. However, configurations, assembly and dimensions of indoor substations are quite different from those of outdoor substations. SF6 Gas Insulated Substations (GIS) are preferred for the following 

EHV, HV Substations.



Substations in urban areas, industrial areas, mountainous regions where land is costly and civil works are complex.



Heavily polluted areas such as sea-shores, industrial areas, thermal power stations etc. Where open terminal substations experience frequent flashovers.



Maintenance free substations.

Besides the main voltage levels, each substation has auxiliary AC and DC distribution systems for feeding the various auxiliary systems, protection systems and control systems. The reference values of auxiliary voltage are mentioned above in in Table -1. High voltage DC Transmission systems (HVDC) have following parts at each end of the HVDC Transmission line. 

EHV AC yard which is at 400 kV AC or 220 kV AC



HVDC yard which is at + 400 kV DC or + 500 kV DC etc.



Valve hall, Converter Transmission and AC Filters.



Electrode line, earth electrode.

Bipolar HVDC system has two poles, one of a positive and other negative polarity with respect to earth. The nominal voltage + 500 kV refers to voltage of the two DC poles with respect to earth.

The

midpoint of converters is earthed through earth electrodes. One HVDC substation is required at each end of the long HVDC transmission line. In case of Back-to-Back HVDC substation, the long distance HVDC transmission line is eliminated and such substation has the following parts: 

AC Switchyard of one grid.



AC Switchyard of other grid.



Back-to-back converter transformers and valves.

Such substations are used for asynchronous links between two AC systems for interconnection. The frequency fluctuations on one AC side are not reflected on the other AC side and the power can be transferred in either directions by adjusting the characteristics of the converter valves. Power can be exchanged rapidly and accurately in a controlled way. 1.4

Types of Substations Back to contents page

The substations can be classified in several ways including the following: i)

Classification based on voltage levels e.g.: AC Substation: EHV, HV, MV, LV; HVDC substation

ii)

Classification-outdoor or indoor.

Outdoor substation is under open sky. Indoor substation is inside a building. iii)

Classification based on configuration, e.g.:

a) Conventional air insulated outdoor substation or b)

SF6 Gas Insulated Substation (GIS)

c) Composite substations having combination of the above two. iv)

Classification based on application.

a) Distribution substation b) Switchyard in Generating Station c) Switching substation (without power transformers) d) Sending-end substation e) Receiving substation f) Factory substation g) Compensating substation e.g. having static var compensation etc. h) Load substation, e.g. arc-furnace substation. Table-2 given below gives the Main Data about a typical 400/230 kV AC Substation. Table 2: Main Data of a Typical 400/220 kV Outdoor AC Substation Operating Voltage Rated current Maximum Short-circuit current in busbar

400 kV

220 kV

2000/3150 A

2000A

40 kA

40 kA

Minimum phase to phase clearance

5.75 m

2.5 m

Minimum phase to earth clearance

3.50 m

2.1 m

2

2

8m

5.5 m

13 m

4m

4” IPS

4” IPS

Number of horizontal levels of tubular busbars/flexible busbars Height of tubular busbars of first level above ground Height of tubular busbar of second level Tubular Aluminium Busbar * * It could be of suitable conductor also. 1.5

Essential Features of a Substation Back to contents page

An AC Substation has following parts:



AC Switchyard



Control Building



DC Battery System and LT Distribution System



Mechanical, Electrical and other auxiliaries



Civil works. An HVDC substation has following main parts:



AC Switchyard



Converter Transformers



AC Filter banks



Valve Halls



AC Switchyard, Smoothing Reactor, DC Filters



Mechanical, Electrical and other auxiliary systems

Each substation is designed separately on the basis of functional requirements, ratings, local conditions predominately based on load centres etc. For the same requirement, several alternative designs are possible. However, the principles and basic technical requirements of all the substations are similar and the substation is designed on the basis of these requirements and the earlier experience. The Rihand-Delhi bipole project is the first commercial long distance transmission project in India employing High Voltage Direct Current (HVDC) Technology. The main features of HVDC which distinguish it from high voltage AC transmission system are: 

It forms an asynchronous connection between two stations connected through HVDC link i.e. the transmission of power is independent of the sending and receiving end AC system frequency.

Due to this, one of the major use of HVDC is to

interconnect two regions which are usually operating at different frequencies. 

HVDC becomes economical for bulk power transfer beyond a certain transmission distance. This is due to the fact that the DC lines are much cheaper compared to the equivalent AC line(s) whereas the terminal equipment of DC are costlier compared to the AC terminal equipments.



Reduction in right of way. The DC line corridor being extremely compact, results in reduction of right of way requirement. The total requirement of the right-of-way reduces to about half, for the same quantum of power to be transmitted.



The power flow through DC link can be precisely controlled under steady state as well as dynamic conditions. During steady state conditions, the power flow remain fixed at the ordered value and is independent of the conditions in the AC system.



During dynamic conditions e.g. during power swings caused by faults, the power flow through DC link can be modulated in a way so as to assist the rest of the grid in damping the prevailing disturbance.



Since a DC transmission line does not generate or absorb any reactive power, it helps to increase the capability of the link to transmit large quantities of power over long distances in an efficient and economical manner. Due to the absence of reactive power, the losses on a DC line are also low compared to an equivalent AC line. Due to absence of frequency factor on DC link, the skin effect does not play any part & complete cross section of the conductor can be effectively used and more power can be transmitted on the same size of the conductor. So HVDC transmission lines help in bulk power transmission in more efficient, economical way on long distances.



The DC transmission linens do not contribute to short circuit levels at the terminals.

This feature becomes important if two large

networks are being connected where short circuit levels are in the vicinity of maximum values specified for the network. In Rihand- Delhi HVDC link of Powergrid one of the converters of the project which operates as rectifier is located in the south eastern corner of UP near Rihand STPP. The other converter which operates as inverter is located in the western side of UP in the district Ghaziabad at Dadri which is about 50 km from Delhi. The project also includes two electrode stations one at Chapki, about 22 km from Rihand and the other at Dhankaur, about 25 km from Dadri. The PLCC communication system has two repeater stations along the route of the

line: one at Katra, about 240 km from Rihand and the other at Jhinjhak, about 325 km from Dadri. The project transmits the power generated at the Rihand/Singrauli complex to Dadri from where it is further distributed to various beneficiaries states/union territories in the Northern Region. Typical Data of Rihand - Delhi HVDC link is given below in Table -3. Table 3: Typical data of Bipolar HVDC Substation (Rihand - Delhi link) 1

Rated Capacity

1500 MW

2

Minimum power

40 MW/80 MW

3

Operating voltage-DC

+ 500 kV

4

AC side voltage range

5

6

For Performance

380-420 kV

For Rating

360-440 kV

AC side frequency range For Performance

48.5-50.5 Hz

For Rating

47.5-51.5 Hz

Negative phase sequence unbalance For Performance

1.0%

For Rating

2.6%

7

Reduced Voltage Oprn.

8

Overload rating

DC, 400 kV

(For 2 hrs, available after every 12 hrs if ambient temp of Delhi or Rihand is more than 33oC 9

Continuous over load

1650 MW 1650 MW

(If ambient temp at Delhi & Rihand is less than 33oC) 10

Short time over load

1000 MW Per pole

(For 5 Sec, available after every 5 min.) 11

Thyristor Valves Thyristor type Max. Voltage per thyristor

YST 45 6.5 kV

Current Rating

12

Continuous

1568 Amp.

2 Hr. Over Load

1725 Amp.

5 Sec. Over Load

2539 Amp.

Converter Type

12 Pulse

13

Valve Type

Quadruple Vertically Suspended, 4 x 96 thyristors

14

Quadruple per Converter

15

Cooling

16

Converter Transformer

3 Water

Type

10, 3 winding

Quantity

6 + 1 Spare per station

Rating

315/305 MVA

Tap Range

+ 14/-10

@ 1.25 % 17

Secondary Voltage For Delhi Delta

206 kV

Star

119 kV

For Rihand

18

19

Delta

213 kV

Star

123 kV

AC Filters Numbers of Banks

3 per station

Numbers of Sub-banks

3

Size of each Bank

230 MVAR

Oil Smoothing Reactor Per pole per station

20

Air Smoothing Reactor Per pole per station

21

180 mH

DC Filters Numbers per pole Tuning Frequencies

22

360 mH

2 12, 24 Hz

PLCC Frequencies Data (pole & bipole)

2400 Bauds

Per pole per station

180 mH

Repeater LAS to CU Speech

600 Bauds 100/50 Bauds

23

24

Station Availability Design target

99%

Guaranteed

97%

HVDC LINE DC voltage

+ 500 kV

Configuration

Horizontal bipole with a pole spacing of 12750 mm

25

Name and type of conductor

26

Number of conductors per pole

27

Insulators

ACSR “BERSIMIS” / 35.1 mm 4 160 kN HVDC disk insulator with zinc sleeve, 38 insulators used in each arm of ` V’ string. Porcelain & toughened glass insulators have been used

1.5.1

Special Features Back to contents page

In order to integrate the project with the AC system and to help the grid, a number of features have been incorporated into the project that take advantages of the HVDC transmission. Some of these features are i) Power modulation Under normal operating conditions a part of the Northern Region Ac system remains parallel to the Rihand-Delhi HVDC project. In case of any disturbance in the AC system e.g. caused by faults, switching actions, the power flow on the HVDC link is modulated to counteract the power swings. Depending upon the need, as determined through minimum power upto the five second overload rating of the HVDC link. ii) Frequency control At Rihand side, the rectifier is connected to the rest of the AC System through two 400 kV AC lines. In case of outages of these lines the power flow through the HVDC link is regulated to prevent the Rihand machines from putting out of the grid and

maintain the frequency of the Rihand generators at a target value near 50 Hz. iii) Reactive power control This feature allows controlled switching of the available Ac harmonic filter (s) (i) to meet the target value of reactive power exchange with the Ac system at Rihand, and (ii) to meet the target value of AC system voltage or reactive power exchange at Dadri. While switching the Ac harmonic filter (s), proper care is taken of the harmonic performance criteria, operating mode, bipole power and the AC system conditions. iv) Run back control The flow through the HVDC link is also regulated following outages of AC lines at Dadri or generators at Rihand. v) Control of sub-synchronous reasonance Suitable subsynchronous resonance damping controllers have been incorporated to prevent any negative damping by the HVDC at the nearby generator’s natural resonating frequencies. This avoids any adverse interaction between HVDC and the generators at the natural resonating frequencies. 1.6

Site Selection Back to contents page

Before the actual

switchyard erection works, the land selected for

setting up the substation is acquired. A Proforma at Annexure- I gives the Format for selection of site for Sub-Station site Annexure-1 Back to contents page

Format for Comparative Statement of Sites For Sub-Stations ______________________________________________________________________________________________

Sl. No. Criteria

Alternate-I

Alternate-II Alternate-III

______________________________________________________________________________________________

1.0

Land

1.1

Size (Acre) (Mtr. x Mtr.)

1.2

Govt. Private/Forest land

1.3

Agriculture/Wasteland

1.4

Development

1.5

Approximate cost

1.6

Type of soil

1.7

No. of owners

1.8

Environment/Pollution in the vicinity

1.9

Location with reference to nearest town

1.10 H.F.L. Data 1.11 Diversion of Nallah/Canal required 1.12 Slope 1.13 Extent of levelling required 1.14 Land acquisition feasibility 1.15 Rate of Govt. land 1.16 No. of owners 1.17 Exten. of approach 1.18 Planned/unplanned development 1.19 Size of sites 1.20 No. of families displaced 1.21 Required Government value 1.22 Level of site with ref. to road level 1.23 Distance from sea shore 2.0

Approach

2.1

What are the Obstacles in reaching site

2.2

Approach road

2.3

Length of approach road

2.4

Distance from main road

2.5

Unloading facility at Railway Station

2.6

No. of Culverts required

3.0

Community Facilities

3.1

Drinking Water

3.2

Drainage

3.3

a)

Post Office

b)

Telephone

c)

Telex

3.4

Market

3.5

Security

3.6

Amendability

3.7

Availability of construction water

3.8

Availability of water

3.9

Nearest EHV line

3.10 Length of line between this site & nearest substation 3.11 Length of line estimate 3.12 Additional crossings 3.13 Frontage for line take off 3.14 Telephone/Telegraph line 4.0

Others

1.6.1

Land Acquisition Back to contents page

Land is a state subject. Land acquisition activity starts after the approval

is

obtained

from

the

competent

authority

for

the

recommended site. Land is to be acquired for starting the construction activities.

Typically for a 400 kV sub-station 50-80 Acre land is

required. Land being the state subject, acquisition for the sub-station land is carried out through land acquisition deptt. of the concerned state govt. Brief summary of Land Acquisition Process is given below 1.6.2

Provisions Under The Land Acquisition Act, 1894 For Sub-Stations Back to contents page

When land is acquired for sub-stations, POWERGRID will follow procedures laid down under the Land Acquisition Act (LA Act), 1894. POWERGRID sub-stations have never resulted in large scale displacement or loss of livelihoods. There have been only marginal impacts due to flexibility exercised by POWERGRID in selecting sites. The LA Act specifies that in all cases of land acquisition, no award of land can be made by the government authorities unless all compensation has been paid. POWERGRID has always followed a schedule for R&R (illustrated in Table below). These will be further reinforced

taking

into

consideration

POWERGRID’s

framework and public consultation process. Table 4: POWERGRID’s Activity Chart for Land Acquisition and R&R Activity 

Submission of cases for land acquisition



Section 4 draft notification



Spot verifications



Scope for objections from public



Publication of Section 6 draft declaration



Marking of land, notice to persons and award by Collector



Finalisation of R&R package



Payment of compensation and acquisition of land



Handing over land to POWERGRID



Implementation and completion of R&R package

entitlement

1.6.3

Land Acquisition Act, 1894 as amended in 1984 Back to contents page

This is the principal law dealing with acquisition of private land by the state

for

“a

public

purpose”.

Progressive

liberalisation

and

industrialisation have led to an increase in compulsory land acquisition. Land acquisition goes through a number of stages starting from notification to payment of compensation. POWERGRID selects a suitable substation site only after the approval of the project by GOI. Attachment above shows the format for comparative statements of sites to be considered for construction of sub-stations. On the basis of data for the various parameters cited in the checklist a comprehensive analysis for each alternative site is carried out. Weightage given to the various parameters is often site specific. Due consideration is given to infrastructure facilities such as access roads, railheads etc.; type of land viz. Govt., revenue, private land, agricultural land; social impacts such as no. of families getting affected; and cost of compensation and rehabilitation. The Activity Chart given in the Annexure-2 shows the time frame for the implementation of various sections of Land Acquisition Act (Section wise time schedule) as well as the time schedule for parallel R&R activities.

Annexure-2 Back to contents page

ACTIVITY CHART (TIME FRAME) LAND ACQUISITION

R&R ACTIVITY (PARALLEL ACTIVITY)

SECTION 16- POSSESSION OF LAND ________ 1 MONTH LINK __________DISBURSEMENT OF COMPENSATION

__________ FINALISATION OF RAP

__________15 DAYS SECTION 11- AWARD BY COLLECTOR 2 MONTHS __________1 MONTH

PUBLIC CONSULTATION

SECTION 9- NOTICE TO PERSONS __________ 1 MONTH COMPLETION OF S-E SURVEY SECTION 8- MEASUREMENT AND MARKING OF LAND 3 MONTHS ___________15 DAYS SECTION 6-DECLARATION OF LAND FOR ACQUISITION ____________2 MONTHS

SOCIO-ECONOMIC SURVEY LINK

BY POWERGRID OR OUT SIDE

AGENCY SECTION 4- PUBLIC NOTIFICATION ___________ 2 MONTHS SUBMISSION OF CASE TO STATE GOVT. FOR ACQUISITION BY POWERGRID

1.7

Substation parts and equipment: Back to contents page

Outdoor Switchyard

-

Incoming & outgoing lines

-

Busbars

-

Transformers

-

Insulators

-

Substation Equipment such as Circuit-

breakers, Isolators, Earthing, Switches, Surge Arresters, CTs, VTs/CVTs -

Neutral Grounding Equipment

-

Station Earthing system comprising

ground mat, risers, earthing strips, earthing spikes -

Overhead earthwire shielding against

lightning strokes, or, lightning masts -

Galvanised steel structures for towers,

gantries, equipment supports -

PLCC Equipment including line trap,

tuning unit, coupling capacitor, etc.

Main Office Building

-

Power cables

-

Control cables for protection and control

-

Roads, Railway track, cable trenches

-

Station lighting system

-

Administrative building conference room etc.

11/ 33 kV Switchgear

-

33 kV Outdoor Switchgear 11 kV Indoor Switchgear

LT Panels Battery room and

-

Low voltage AC. Switchgear

-

Control Panels, Protection Panels.

-

DC Battery system and charging equipment distribution system

Mechanical, Electrical

-

Fire fighting system Oil purification

system and other auxiliaries Substation parts and equipment:

Protection system

SCADA(Supervisory

-

Cooling water system

-

Telephone system

-

Workshop; stores etc.

-

CTs, CVTs

-

Protective Relays

-

Circuit breakers

-

Computer/Microprocessors, Data collection

Control and Data

-

system, Data processing system

Acquisition System)

-

Man-machine interface

-

Expert system etc.

1.8

Functions of Sub-station Equipments & Associated Systems Back to contents page

i)

Circuit Breakers Circuit Breakers are the switching and current interrupting devices. Basically a circuit-breaker comprises a set of fixed and movable contacts. The contacts can be separated by means of an operating mechanism.

The separation of current carrying

contacts produces an arc. The arc is extinguished by a suitable medium such as dielectric oil, vacuum, SF6 gas.

The circuit

breakers are necessary at every switching point in the substation. ii)

Isolators Isolators are disconnecting switches which can be used for disconnecting a circuit under no current condition. They are generally installed along with the circuit breakers. An isolator can be opened after the circuit breaker. After opening the isolator, the earthing switch can be closed to discharge the trapped electrical charges to the ground.

iii)

Current Transformers and Voltage Transformers

These transformers are used for transforming the current and voltage to a lower value for the purpose of measurement, protection and control. iv)

Surge Arresters Surge Arresters divert the over voltages to earth and protect the substation equipment from over voltage surges.

v)

Busbars Busbars are either flexible or rigid. Flexible busbars are made of ACSR conductors and are supported on strain insulators. Rigid busbars are made up of aluminium tubes and are supported on post insulators.

vi)

Galvanised Steel Structures Galvanised Steel Structures are made of bolted/welded structures of angles/channels/pipes. These are used for towers, gantries, equipment, support structures etc.

Galvanised

structures provide rigid support to the various equipments and insulators. The design should be safe and economical. vii)

Power Line Carrier Current Equipment PLCC is necessary for transmitting/receiving high frequency signals over the power line (transmission Line) for the following: a)

Voice communication

b)

Data transmission

c)

Protection signalling

d)

Control signalling

A small power system is generally controlled by direct supervision of generating stations and substations through respective control rooms. A large network having several generating stations, substations and load centres is controlled from central load despatch centre. Digital or voice signals are transmitted over the transmission lines via the substations. The substations are linked with the load control centres via Power Line Carrier System (PLCC)/ microwave links and P&T phones. The data collected from major substations and generating stations is transmitted to the load control centre.

The

instructions from the load control centres are transmitted to the

control rooms of generating stations and substations for executing appropriate action. Modern power system is controlled with the help of several automatic, semi-automatic equipments. Digital computers and microprocessors are installed in the control rooms of large substations, generating stations and load control centres for data collection, data monitoring, automatic protection and automatic control. viii)

Protective Systems in Substations A fault in its electrical equipment is defined as a defect in its electrical circuit due to which the flow of current is diverted from the intended path. During the fault the impedance is low and fault current is high. Fault currents being high, can damage the equipments thro’ which it flows. Fault in certain important equipment can affect the stability of the power system. For example, a fault in the bus zone of a substation can cause tripping of all the feeders and can affect the stability of the interconnected system. The relays distinguish between normal and abnormal condition. Whenever an abnormal condition develops, the relay closes its contacts. Thereby the trip circuit of the circuit breaker is closed. Current from the battery supply flows in the trip coil of the circuit breaker and the circuit breaker opens and the faulty part is disconnected from the supply. The entire process, ‘occurrence of fault-operation of relay opening of circuit breaker to removal of faulty part from the system’ is automatic and fast. Besides relays and circuit breakers, there are several other important components in the protective relaying scheme, these include : protective current transformers and voltage transformers, protective relays, time delay relays, auxiliary relays, secondary circuits, trip circuits, auxiliaries and accessories, etc.

Each

component is important. Protective relaying is a team work of these components. The function of different substation equipments and systems are tabulated below in Table -5.

Table 5: Functions of different Substation Equipments & Systems Sl.

Equipment

Function

No. 1.

Bus-bar

Incoming and outgoing circuits connected to bus-bar

2.

Circuit-breakers

Automatic

switching

during

normal

or

no-load

condition

abnormal

conditions. 3.

Isolators

Disconnection

(Disconnectors)

isolation and maintenance.

4.

Earthing Switch

To discharge the voltage on dead lines to earth.

5.

Current

To step-down currents for measurement, control, and

Transformer

protection.

Voltage

To step-down currents for measurement, control, and

Transformer

protection.

Lightning Arrester

To discharge lightning over voltage and switching over

(Surge Arrester)

voltage to earth.

Shunt reactor

To provide reactive power compensation during low

6. 7. 8.

under

for

safety,

loads. 9.

Series Reactors

To reduce the short-circuit current or starting currents.

10.

Neutral-Grounding

To limit the earth fault current

Reactors 11.

Coupling capacitor

To provide connection between high voltage line and power line carrier current equipment.

12.

Line-trap

To prevent high frequency signals from entering other zones.

13.

Shunt capacitors

To provide compensations to reactive loads of lagging power factors.

14.

Power Transformer To step-up or step-down the voltage and transfer power from one AC voltage to another AC voltage at the same frequency.

15.

Series capacitors

Compensation of long lines

16.

Substation

To provide an earth mat for connecting neutral points,

Earthing

equipment body, support structures to earth. For safety

(Grounding)

of personnel and for enabling earth fault protection. To

System

provide the path for discharging the earth currents from

-Earth mat

Neutrals, Faults, Surge arresters, overheads shielding

-Earthing spikes

wires etc. with safe step-potential and touch potential.

-Earthing risers 17.

Overhead earth

To protect the outdoor substation equipment from

wire shielding or

lightning strokes.

lightning Masts. 18.

Illumination system To provide illumination for vigilance, operation and (lighting)

maintenance.

-for switchyard -buildings -roads, etc. 19.

Protection System

To provide alarm or automatic tripping of faulty part from

-protection relay

healthy part and also to minimise damage to faulty

panels

equipment and associated system.

-control cables -circuit-breakers -CTs, VTs, etc. 20.

Control cabling

For protective circuits, control circuits, metering, circuits, communication circuits.

21.

Power cables

To provide supply path to various auxiliary equipment and machines.

22.

PLCC system

For communication, telemetry, tele-control, power line

power line carrier

carrier protection etc.

current system -line trap -coupling capacitor -PLCC panels

23.

Fire fighting

To sense the occurrence of fire by sensors and to initiate

system

water spray, to disconnect power supply to affected

-sensors, detection region to pin-point location of fire by indication in control system

room.

-water spray system -fire protection control panels, alarm system -water tank and spray system 24.

Cooling water

This system is required for cooling the valves in HVDC

system(HVDC)

substation.

-coolers -water tank -piping -valves 25.

Auxiliary stand by

For supplying starting power, stand by power for

power system

auxiliaries.

-diesel generator sets -switchgear -distribution system 26.

Telephone, Telex

For internal and external communication.

system, Microwave system 1.9

Substation Layouts, Busbar Schemes Back to contents page

The term layout denotes the physical arrangement of various components in the substation relative to one another.

Substation

layout has significant influence on the operation, maintenance, cost

and protection of the substation and these aspects are considered while designing the substation layout. The reasoning behind the connections of components in each circuit and the busbars layout should be understood. Within the frame-work of the basic requirements, the substation layout can have several alternative arrangements. The substation layouts are selected on the basis of the size, the ratings, importance, local requirements and the prevailing practice of the supply authorities. The different bus-bar schemes in a substation with their relative advantages/disadvantages are described below: The choice of busbar schemes for AC yards depend upon several factors mentioned above. The important busbar schemes include the following: 

Single busbar



Double busbar with one breaker per circuit.



Double busbar with two breakers per circuit.



Main and transfer bus



Ring bus



Breaker and a half arrangement



Mesh arrangement etc.

Table : 6 Various Bus-Bar Schemes Sl.

Scheme

Application

No. 1.

Single bus-bar

Remarks

Low voltage and medium -

Cheapest

voltage substations

Total shutdown in case of a

-

Not preferred for important/ large substations

fault -

In case of maintenance of circuit breaker, associated feeder has also to be shut

2.

Duplicate Bus

High voltage substations

-

down Costlier than single bus

-

One bus can serve as a reserve.

-

During

maintenance

or

fault, the reserve bus is used -

More flexibility of operation

-

Buses

are

sectionalised coupler

sometime &

the

bus

breaker

is

connected in between two 3.

Double and

Main Important EHV substations

-

Transfer

buses Additional

flexibility

for

operation

Bus

-

Fault on one bus will not cause a complete outage of

4.

Breaker

&

half scheme

a Important

400

kV -

substations

the station. Uses three breakers for two circuits

-

High flexibility operations

-

Higher costs

-

Suitable

for

those

substations which handle large amounts of power on each circuit

5.

Mesh System

Used for large substations having many incoming and outgoing circuits.

Costlier Gives

good

operational flexibility -

Suitable

where

no.

of

circuits are comparatively few & chances of future expansion are less 1.10

Construction/Erection Drawings Back to contents page

Lists of construction/erection drawings used during Civil and other construction activities in a substation are enclosed at Annexure-3 and Annexure-4.

Annexure-3 Back to contents page

A.

Control Room Building

1.

Ground floor Plan & Elevators

2.

Mezzanine Floor Plan & Elevations

3.

Elevation, Section & Terrace Plan

4.

Foundation Plan-Excavation drawing

5.

Foundation & column up to first floor

6.

Details of plinth beams

7.

Mezzanine floor beams & reinforcement details

8.

Mezzanine floor slab & reinforcement details

9.

Mezzanine floor insert details

10.

Lintel & Chhajja details

11.

Roof slab reinforcemet details

12.

Roof beam details

13.

Roof slab insert details

14.

Details of foundation for A/C plant room

15.

GA & RCC details of foundation for cooling tower supporting structure

16.

Internal cable trench details

17.

Details of steel & window details

18.

Aluminium glazing window details

19.

Fire resistance door/siding door details

20.

Details of toilet & pantry

21.

Plumbing details

22.

Details of septic tank

23.

Finish schedule

24.

Colour scheme

25.

Electrical wiring drawings

B.

DG Set Building

1.

Plan elevations and sections

2.

Foundation layout and RCC details of slab flooring, columns, beams.

3.

Details of brick wall foundation, columns and intel.

4.

Details of doors and windows.

5.

DG set foundation and cable trench layout and

R/F details.

6.

Colour scheme and misc. details, monorail fixing details.

7.

Electrical wiring, insert fixing details.

C.

F.F. Pump House

1.

Plan, elevation and sections

2.

Foundation layout, RCC details of slab, footing, column beam.

3.

Terrace plan and Misc. Details.

4.

Details of water tanks.

5.

Details of doors, window, ventilators and rolling shutters.

6.

Equipment foundation, cable trench layout and reinforcement details.

7.

Electrical wiring drgs., insert details.

D.

Internal Roads and Drains

1.

Layouts of internal roads and drains.

2.

Layouts and cross sectional details of roads and drains.

3.

Layout of culverts and drains.

4.

Details of culverts and drains.

E.

Boundaries Wall and Fencing

1.

Boundaries wall and fencing details

2.

Fencing and gate details

F.

Shunt Reactors

1.

GA and foundation details.

2.

Pylon support details

G.

Auto Transformer

1.

GA and RCC details of foundation, General arrangement

2.

Pylon support details

3.

Details of rail track

4.

Fire protection wall between auto-transformer

H.

Approach Roads and Drains

1.

Layout of approach roads and drains.

2.

Layout and C/S details of roads and drains.

3.

Layout of drains and culverts

4.

Details of culverts and drains.

I.

Site Office and Store Complex

1.

Material store plan, Elevation and sections

2.

Crane store plan, Elevationa and Sections.

3.

Site office plan, Elevation and sections.

4.

S/S store Plan, Elevation and sections.

5.

Cement store Plan, Elevation and sections.

6.

Details of raised platform.

7.

Store complex layout plan.

8.

Store complex TL material store.

9.

Store complex TL material store.

10.

Crane store foundation plan, roof plan and beam details.

11.

S/S store foundation plan, roof plan and beam details.

12.

Cement store foundation plan, roof plan and beam details

13.

Details of entrance gate and fencing

14.

Type section of tabular truss.

15.

Details of doors and windows.

16.

Finish schedule of site office and store complex.

17.

Layout ext. drainage and sewerage system

18.

Details of septic tank and soakpit.

19.

Toilet and kitchen detail-site office

20.

Toilet and kitchen details-S/S. store

J.

Structural arrangement

1.

Design of towers and beams

2.

Fabrication drawings of tower & beams

3.

Tower foundation and their designs

4.

Design of equipment supporting structure

a)

CT

b)

CVT

c)

LA

d)

Bus Post Insulator

e)

Isolator

f)

Wave Trap

g)

Circuit Breaker

5.

Equipment supporting structure fabrication drawings

a)

CT

b)

CVT

c)

LA

d)

Bus Post Insulator

e)

Isolator

f)

Wave Trap

g)

Circuit Breaker

6.

Details of foundation bolts

a)

Equipment Structure

b)

Gantry Structure

7.

Design of equipment foundations & foundation details

8.

Cable trench layout

9.

Cable trench section details

10.

Cable trench road crossings

11.

Marshalling box foundation

12.

Sump pit

List of construction Drawings for Township Work in a typical Sub-station A.

Quarters for Type A,B, C and D

1. Architectural plan, Elevation 2. Architectural section, terrace plan 3. Foundation plan, Plinth beam layout 4. Details of foundation 5. Details of roof slab, first floor slab, lintel etc. 6. Electrical layout 7. Sanitary layout and plumbing details A.

Master Layout

1. Plan 2. Electrical layout 3. Sewerage layout 4. Plumbing layout 5. Layout of drains and road. B.

Overhead and underground Water-Tank

1.

Architectural Drawings’

2.

Structural details

3.

Foundation Details

C.

Non Residential Buildings (Nursery school, Dispensary and shopping centre)

4.

Architectural plan and Elevation

5.

Structural Details

6.

Services

D.

Administrative Building

7.

Architectural plan and Elevation

8.

Structural details

9.

Services

Annexure-4 Back to contents page

List of drawings for a typical Sub-station A.

Sub-Station Drawings

1.

Single line diagram

2.

General arrangement of substation’

3.

Electrical layout (Plan and Section)

4.

Electrical clearance diagram

5.

Switchyard structural layout arrangement

6.

Layout of equipment structures

7.

Busbar support design and design calculations

8.

Cable trench layout and foundation plan

9.

Details of cable trench section

10.

DSLP calculation

11.

Drawing of DSLP scheme

12.

Earthmat design calculation

13.

Equipment/structure earthing details (List all relevant drawings, under this heading)

a)

Earthmat layout

b)

Erection key diagram (Plan and Section)

c)

Bill of Quantity

14.

Short circuit force and critical span calculation(for spacers)

15.

Design calculation for sag-tension and stringing chart

16.

Power cable schedule

17.

Inter pole cable schedule

18.

Buried cable trench layout

19.

OGA drg. for bus post insulator

20.

Individual insulators detail drg. for bus post insulator

21.

Detail drg. for bottom & inermediate flanges

22.

Cap detail drg. for bus post insulator

23.

Corona ring for bus post insulator

24.

GA of bay marshalling kiosk

25.

Schematic & wiring diagram of bay marshalling kiosk

26.

Tension/suspension string insulator and hardware assembly

27.

120KN antifog disc insulator GA drg.

28.

Clamps, connectors and spacers GA drg.

29.

ACSR conductor, Al tube & shieldwire

30.

GTP data sheets

31.

Cable trays GA drawing

32.

GA drg. for double compression type cable gland

33.

Drum drg. for ACSR conductor and earthwire

B.

245KV SF6 Circuit Breaker

1.

Outline general arrangement drawing of C.B. indicating major parameters.

2.

Outline general arrangement drg. of control cabinets and their foundation plan and separate drawing showing component layout.

3.

Outline general arrangement drg. of support insulator.

4.

Interrupter insulator, insulator & insulator for grading capacitor showing clearly the shed profile and parameters.

5.

Support structure and foundation plan drawing with necessary support structure design calculations.

6.

Electrical schematic diagram including brief write up on operation.

7.

Rating and name plate drawing.

8.

Air/SF6 gas connection diagram

9.

Schematic diagram of electro hydraulic operated mechanism in case of hydraulic drive.

10.

Wiring diagram

11.

Terminal conenctor and corona ring drawings

12.

Sectional view of SF6 gas couplings.

13.

Sectional view of interruptor, voltage grading device identifying each part of the assembly.

14.

Following additional drawings for Unit air compressor:

a)

Foundation plan and details for compressor and motor

b)

Unit of contact manometer assembly.

C.

245KV Isolator

1.

Outline drawing of isolators with one E/S

2.

Outline drawing of isolators with two E/S

3.

Outline drawing of isoaltor without E/S

4.

General arrangement of contact assembly.

5.

Terminal pad and hinge contract.

6.

Loading data.

a)

GA of motor operated mechanism

b)

GA of support insulator

7.

Details of constructional interlock

8.

Name Plate details

9.

Drawings for terminal connector & corona rings.

10.

Drawing for base frame.

11.

Schematic drawings.

12.

Wiring diagram & inerpole connection diagram.

13.

Drawing for motor operated mechanism/manually operated mechanism, as applicable with door open and identifying all parts of the mechanism and the control panel.

14.

Drawing for support structure.

D.

245KV Current Transformer

1.

Outline drawing of C.T. indicating major parameters.

2.

Sectional view of C.T.

3.

OGA of marshalling box

4.

OGA of secondary terminal box

5.

Wiring diagram of marshalling box(including interpole wiring).

6.

Magnetisation curve.

7.

Name plate.

8.

Drawing of terminal connectors.

9.

Drawing of corona ring.

10.

Drawing for stool/sub-structure, if applicable.

11.

Drawing for support structure.

E.

245KV Capacitor Voltage Transformer

1.

Outline drawing of CVT indicating major parameters.

2.

Sectional view of CVT.

3.

OGA of secondary terminal box.

4.

OGA of marshalling box.

5.

Wiring diagram of marshalling box (including interpole wiring)

6.

Drawing for terminal connectors

7.

Name plate drawing.

8.

Drawing for stool/sub-structure, if applicable.

9.

Drawing for support structure.

F.

245KV Class Surge Arrester

1.

OGA of Surge Arrester indicating major parameters.

2.

Foundation details.

3.

Insulating base drawing.

4.

Discharge counter/surge monitor drawing

5.

Method of connecting surge monitor with SA

6.

Electrial schematic diagram of surge monitor

7.

Ground terminal bracket details

8.

Name plate drawing

9.

Line teminal bracket drawing along with corona rings

10.

Residual voltage verses discharge current curves

11.

Drawing for stool/sub-structure, if applicable

12.

Drawing showing internal view of SA

13.

Drawing of Insulator

14.

Drawing showing pressure relief arrangement

15.

Support structure drawing.

G.

Power and Control Cables

1.

Data sheet of all types of power cables

2.

Data sheet of all types of control cables

3.

Power cable schedule

4.

Control cable sizing/section criteria

5.

Control cable laying & termination schedules

List of Drawings for Erectin of C&R panels in a typical Sub-Station 1.

Data requirement sheet with literature.

2.

Type test report for all equipments.

3.

Board formation redrawings.

4.

Foundation details.

5.

General arrangement of control panel/feeder.

6.

General arrangement of relay panel/feeder.

7.

Schematics of control panel/feeder.

8.

Schematics of relay panel/feeder.

9.

Cable schedule.

a) Inter panel schedule. b) Cable laying schedule. c) Cable terminating schedule. 10.

Equipment layout drgs.

11.

Relay settings.

12.

As built drgs. And manuals for circulation.

List of drawings for Erection of PLCC panels in a typical Sub-Station 1. Data requirement sheet with literature. 2. Type test report for all equipments. 3. General arrangement of PLCC system. 4. Equipment drgs. a) PLCC panel for speech and data. b) PLCC panel for speech and protection. c) Protection couplet. d) Wave Trap. e) Coupling Device. f) EPAX g) 4 wire/2 wire Telephone 5. Frequency Plan 6. As built drawing

Chapter-2 SWITCHYARD CIVIL WORKS

CHAPTER

TWO

SWITCHYARD CIVIL WORKS Back to contents page

2.0

Introduction Back to contents page

Civil works in a substation mainly comprise of :  Construction of equipment foundations transformer/reactor plinth, structure foundations  Cable trenches  Fencing around switch yard  Surface treatment, ground filling and sloping  Water supply system & Sewerage system  Construction of roads and drains  Construction of control room building, compressor room, offices, repair / maintenance bay and other non-residential buildings  Construction of railway, siding and railway track if required  Construction of residential colony  Horticulture works  Administrative Building, community centre, guest house/transit Camp, shopping complex & nursery school etc. For carrying out the various civil works at site which is initially an open barren/cultivated land, initially survey of land is carried out alongwith the soil investigation. Survey is done to finalise the levels of switchyard, roads and design & layout of drainage system in the switchyard as well as in the township.

Fix & permanent bench mark is provided for

adopting it as a reference point for various works like laying out of control room, erection of gantries and various equipments, foundations and buildings in the switchyard that are done in reference to this permanent bench mark. Now grid lines are required to be marked in East-West and North-South direction by erecting the concrete grid

pillars. Grid lines are marked on the land to fix the direction & orientation of various civil structures with reference to some fixed bench mark on the site. These gridlines help in implementing the erection, orientation and layout of foundations for various equipments & control room building which is later on helpful in laying out the other equipments and structures on the land. 2.1

Soil Investigation Back to contents page



Soil investigation is carried out at site and result of soil investigation are forwarded to Corporate Centre for design of various foundations.



Detailed soil investigation is carried out at site to arrive at sufficiently accurate, general as well as specific information about the soil profile and necessary soil parameters of the site in order that the foundations of various structures can be designed and constructed safely & rationally.



The soil investigation tests should be conducted at all the critical locations i.e. control room building, auto transformer, shunt reactor, lightening masts, 400 KV tower locations etc.



Engineering

department

at

Corporate

Centre

prepares

the

foundation drawings and approved drawings are sent to site for casting. 

Engineering Department also releases various other erection drawings for different works like cable

trench design drawings,

cover slab design drawings, overall layout of equipments in switchyard, equipments erection key drawings etc. for erection works at site.

During this period, the site levelling work is carried

out at site in order to smoothen the undulations. 2.2

Levelling Back to contents page

The land acquired for substation may be barren/cultivated land. The soil may be rocky, black cotton, sandy or any other type. The acquired land may contain trees, bushes, crop, drains, etc. that require cleaning/ clearing before starting the levelling works in the yard.

i) Switchyard area is important and preferably it should be brought to a single level.

However, in only unavoidable circumstances or

where it is uneconomical to go for levelling the soil than keeping a multi-layered/in steps levels, the different levels may be kept. ii)

Levelling may also be required in township area for bringing the land to a single level for designing the drainage system and residential quarters. In case of too much level difference the residences (categories) may be designed at different uniform levels but with good drainage system to avoid water logging.

iii) Before starting the levelling works the marked area of switchyard is cleaned. Any crop, bushes, trees, shrubs and structure that may cause hindrance or that are undesired are cleared from the yard area. iv) Any drain, telephone line, building structure is also removed from the switchyard area, to a nearby suitable place. v)

Now spot levels will have to be taken in the yard area before making an assessment for the levelling i.e. for assessing the requirement of soil for low level areas and cutting of soil from high level area to bring the whole yard area to a normal formation level.

vi) In the ideal case of levelling there is no requirement for borrowed earth and quantity of earth excavated from the high level and fill it in the low lying areas is equal. This is the most economical method of levelling. Care is to be taken such that the earth is not excavated below the formation level. vii) For compaction earth is filled in the low lying areas in layers of 20 cm thickness then watered and compacted by rollers/ dozers. viii)The method and equipment used to compact the fill material to a density that will give the allowable soil bearing pressure required for the foundations, roads, etc. In each layer of fill material. Each layer of earth embankment when compacted should be as close to optimum moisture as practicable.

Embankment material which

does not contain sufficient moisture to obtain proper compaction should be wetted. If the material contains an excess of moisture, then it should be allowed to dry before rolling by hand rollers/dozers. No compaction is carried out in rainy weather.

ix) Sometime in hills or in rocky soil, we may have to go for blasting the earth at higher levels. The blasting is done in the specified manner. All safety precautions should be taken while blasting so as to avoid any injury/loss of life and property. The explosive material used for blasting should be handled very carefully.

While applying the

explosive material for blasting, one should take care such that the earth excavated/hole created by blasting is upto/very near the desired ground level. x) The levels in the entire area (after finishing the levelling work) should be taken and checked up with the desired formation level. Final dressing up and finishing should be done in case if levels are not found satisfactory. The care should however be taken during compaction. Measurement for levelling work (i.e. excavation & filling) is a cumbersome process and it should be done strictly as per the specifications. All the level records must be noted in field levelling book duly signed by the concerned personnel of contractor of site. The drawings of level before starting the levelling and then final levels should be maintained. The measurements should be recorded very carefully as per the technical specifications. Care should be taken that with the movement of trucks, dozers etc. any other structure in the vicinity is not affected or uprooted. 2.3

Foundations Back to contents page

Foundations in switchyard area the foundations are cast for: i)

Lattice Structure (Tower foundations) i.e. for gantries, lightening masts etc.

ii)

Cable trenches

iii)

Equipment in switchyard



Based on the approved layout drawings furnished by Corporate Engineering the foundations are marked on the ground.



While marking the foundations on the ground their layout should be strictly verified with the layout drawings as well as with the bench mark/grid lines on site with great accuracy.



Layout of the various switchyard equipments is also verified with the layout drawings and with respect to gridlines on the ground. For further confirmation, the control room building co-ordinates can be used and necessary rectification in the layout & orientation of various equipments and foundation can be made.



Any changes in layout if desired should be brought in the notice of Corporate Engineering and necessary amendments should be approved. It is a good practice to have a second confirmation for marking the various foundations w.r.t. control room co-ordinates that are fixed and marked before hand.



Foundations for various lattice structure are cast in the switchyard area. The type of foundation is decided based on the type of soil. Engineering Department at Corporate Centre provides the necessary tower foundation, excavation and concreting work drawings based on the soil investigation reports furnished to them.

2.4

Foundations for Transformer & Shunt Reactors Back to contents page

i)

Transformer of 400/220/33 kV, 315 MVA capacity is generally provided at our substation sites. Transformer and shunt reactors are the major equipments in switchyard.

Their transportation,

storage, foundation and installation require special techniques and efforts. ii)

Transformer & shunt reactor foundation work includes the supply of a permanent track system to enable the replacement of any failed unit by the spare unit located at the site. It also includes the concreting, providing jacking pads, steel work for the MS grating and providing the anchoring arrangement.

iii)

The foundations for transformer & shunt reactor should be ready in advance before actual receipt of the equipments. Proper coordination in the works are required so that the foundations are completed well in advance.

iv)

For casting the foundation of Transformer & Shunt Reactor the marking is done as per the approved drawings from the Corporate

Engineering Department. The marking of co-ordinates should be checked properly and reconfirmed with the control room and switchyard layout co-ordinates.

The pylon supports that are

required to be laid before the concreting works is generally in the scope of fire fighting contractor. Scheduling of such works should be co-ordinated between the contractors for smooth working & to avoid any stoppages in work. 2.5

Cable Trenches in Switchyard Back to contents page

i)

The cable trench drawings are received by site from the Corporate Engineering Department Based on these drawings cable trenches are cast at site.

ii)

The cable trenches are marked on ground and excavation is started by the contractor on the marked trenches.

iii)

Before starting the RCC the land should be levelled, smoothened and then laid with PCC of required thickness. Proper care should be taken during RCC casting.

iv)

The centre line of cable trench (marked before excavation) should be rechecked during the lean concerning to avoid any mistakes in marking.

v)

The slope in cable trenches is provided in such a way that the water from secondary cable trenches flows towards the primary cable trenches. The slope of primary cable trench is maintained in such a way that the rain water may go in a sump on the other side of the primary cable trench by gravity itself.

vi)

Before starting the concreting, shuttering is provided for cable trench walls. Provision should be made at this time to insert the cable supporting angles and other steel reinforcements in the cable trench walls.

vii)

Concreting of cable trenches can be started after all the wall inserts bends etc. have been inserted properly. Necessary expansion joints generally made up of PVC or specified material of designed size should be inserted at the specified length of cable trench walls.

viii) Top of the trenches is kept at least 150 mm (or as specified) above the furnished ground level such that the surface rain water does not enter the trench. ix)

All metal parts inside the trench are connected to the earthing system.

x)

Trench wall should not foul with the foundations. Suitable clear gap is maintained.

xi)

A slope of 1/500 is provided in the trench bed along the run and 1/250 perpendicular to the run or as specified.

xii)

All construction joints of cable trenches i.e. between base slab to base slab & the junction of vertical wall to base slab as well as from vertical wall to wall and all the expansion joints are to be provided with approved quality PVC water stops of the specified size. This is required in all the sections where the ground water table is expected to rise above the junction of base slab and vertical wall of cable trenches.

xiii) All the inserts exposed surfaces are be brushed with metal wire brushes. xiv) Cable supports are welded at the right level and painted with the specified paint. xv)

All cable trenches are cleaned after the cable trench work is completed.

2.6

Cable Trench Cover Slabs Back to contents page

i)

Precast removable concrete covers are to be provided on the cable trenches.

ii)

These covers slabs are designed to cover the open trenches in which cables are placed.

iii)

Concrete cover slabs are cast by using metallic shuttering of suitable size.

iv)

The shuttering should not be deformed otherwise cover slabs will also be deformed and become out of shape.

v)

After casting the slabs, shuttering should be removed after 24 hrs. and proper curing of cover slabs should be done for at least 10 -14 days.

vi)

Cover slabs are placed over the cable trenches after the cables have been laid.

vii)

The cover slabs over cable trench are joined with cement mortar and generally the tenth cover in a line is kept free from joining with provision of lifting hook. This is done so that the covers can be removed for regular inspection of cable trenches during maintenance.

viii) Cover slabs are placed on cable trenches after completion of cable laying. 2.7

Anti-weed Treatment, Micro Levelling Gravel Filling & Metal Spreading Back to contents page

2.7.1

Anti-weed Treatment Back to contents page

i)

The soil of the entire switchyard area is subjected to sterilisation/anti-weed treatment before the site surfacing/gravel fill material. The treatment is done strictly as per instruction of the manufacturer of the chemical required for soil sterilisation/antiweed treatment.

ii)

After all the structures and equipments have been erected and accepted, and soil sterilisation (as specified) is complete, the site should

be

maintained

to

the

lines

and

levels

and

rolled/compacted by using roller of specified capacity with suitable water sprinkling to form a smooth and compact surface condition which should match with finished ground level of the switchyard area. 2.7.2

Micro Levelling Back to contents page

i)

After the soil sterilisation and application of anti weed treatment the surface is prepared for levelling to the required level.

ii)

The switchyard are is used by various contractors & executing agencies for the various works like laying of earth mat excavation, foundation casting & backfilling of earth, equipments erection, cable laying in the cable trenches and piping work for fire fighting systems.

iii)

After completion of different works the various agencies working in switchyard should remove their set up like construction power cables, water pipe lines, sand, metal & other construction materials and T&P etc.

iv)

The heavy vehicles like cranes, trucks and other transport modes move in the switchyard area. This movement causes a change in the switchyard level causing lot of undulations in the earth level. The earth that was earlier levelled now again requires some fine levelling to bring it back to original finished desired level.

v)

This process of removing the surplus earth and filling it at the low lying areas so as to maintain one level is done after completion of various works in switchyards.

This laid earth is then duly

compacted. vi)

The method of compaction is same that water is poured over, the layer of specified check thickness of earth and the layer of such earth is then compacted using compaction tools. Again a layer is laid and water is poured in it and the earth is again compacted.

vii)

This process of refilling and compaction goes on until the required level of earth is achieved. Care should however be taken that during excavating the excess earth (for refilling at the low level) the earth is cut and removed only upto the required level and not below otherwise this area may again require some refilling causing wastage of labour.

viii) The important thing in micro levelling is the backfilling and compaction. If both are not done properly the earth level may come down after some time (after rains etc.) making it low lying area. In case of some reservations over the degree of compaction of backfilling the specified tests can be performed. 2.7.3

Metal spreading in Switchyard Back to contents page

i)

The area where metal spreading is to be done is measured for quantity of metal required for filling.

ii)

Hard granite store of 40 mm nominal size is spreaded in different stages. Under size and over size metal should be rejected.

iii)

The metal stacks are placed at a designated place and these are measured and recorded before actually spreading in the switchyard metal is spreaded in the layers of 100 mm.

DO’S DON’T’S & SPECIAL PRECAUTIONS

2.8

Do’s , Don’ts & Special Precautions Back to contents page

i) Whenever water table is met during the excavation, it should be dewatered and water table maintained below the bottom of the excavation level during excavation, concreting and backfilling. ii) The method and equipment used to compact the fill material should be suitable to achieve the density that will give the allowable soil bearing pressure required for the foundations, roads etc. In each year of fill material. iii) Minimum 75 mm thick lean concrete (1:4:8) or as specified should be provided below all underground structures, foundations, trenches etc. To provide a base of construction. iv) Necessary protection to the foundation work, if required should be provided to take care of any special requirements for aggressive alkaline soil, black cotton soil or any other type of soil which is detrimental/harmful to the concrete foundations. v) RCC columns should be provided with rigid connection at the base. vi) Only approved admixtures should be used in the concrete for the Works.

When more than one admixture is to be used, each

admixture is batched in its own batch and added to the mixing water separately before discharging into the mixer. vii) The water-reducing set-retarding admixture if used should be of approved brand viii)The

water

roofing

cement

additives

shall

be

used

as

required/advised by the consignee. ix) The concreting of trench should be arranged for a length of not more than 30 mtrs. at a time. x) Bar bending schedule for raft and trench wall should be prepared as per the drawing and same should be checked for placement. xi) To meet the commissioning schedules, the priority areas are to be identified and the construction of foundations and cable trenches should be taken up in stages and priority-wise.

xii) Wherever earth mats are crossing the cable trench suitable U bends of MS rounds should be placed below the trench raft before concreting. xiii)A separate sump should be constructed for curing the cover slabs. xiv)The cover slab should be kept in water sump for a period of about 10 days for curing. xv) Due care should be taken so as not damage any foundation structure or equipment during rolling/compaction. xvi)The gravel should be allowed to come from one or two approved quarries where the similar gravel availability is possible. xvii)The stone should be hard, coarse and it should not be flat. xviii)The quantity required to fill up a measured area should be ascertained actually.

Then the metal of adequate measurement

should be spread in this area. xix)Use of undersize & oversize metal than the specified size should be avoided. A 20 mm sieve can be used to remove the oversized gravel. xx) The material required for site surfacing/gravel filling should be free from all types of organic materials and should be of standard approved quality, and as directed by the Engineer-in-charge. xxi)The rail and concrete sleepers are required for providing the track for transformer and shunt reactor unit. These items are required to be procured from the market. The items are of specific dimension and requirement. Their availability in the open market may not be easy so efforts to procure these items should be started simultaneously while the works for foundation are started.

CHECK FORMAT

2.9

Check Format Back to contents page

1.

Soil investigation report has been approved by competent authority

Yes/No

2.

Construction drawings are being released by Engg. deptt.

Yes/No

3.

Grid pillars are erected at site.

Yes/No

4.

Grid lines are formed as per designed layout at site

Yes/No

5.

Centre line marking for cable trench is checked as per drawing

Yes/No

6.

Proper slope of main and all secondary cable trenches is Yes/No maintained

7.

Bar bending schedule trench walls and raft is approved

Yes/No

8.

Nosing angles and inserts for fixing cable supports have been Yes/No provided in trench wall

9.

For concreting proper shuttering is provided in cable trenches

Yes/No

10.

Required water stoppers at the specified trench length has been Yes/No provided

11.

Concreting of trenches/raft done as per specifications

Yes/No

12.

U bends have been provided in cable trenches where these cross Yes/No the earth mats.

13.

For equipment foundations location exact co-ordinates are verified

Yes/No

14.

All levelling work is complete before start of foundations

Yes/No

15.

All materials like sand, cement, metal, foundation bolts etc. are Yes/No available with adequate T&P before start of foundation activities

16.

Cable trench cover slabs being cast on special platform and with Yes/No proper shuttering

17.

Proper curing of cover slabs is being done

Yes/No

18.

When placed on trenches (after cable laying etc.) joints have been Yes/No sealed

19.

For transformer & shunt reactor foundations pylon supports have Yes/No been provided by the concerned agency

20.

Layout of foundation is verified with switchyard layout drawing

Yes/No

21.

Rail and sleepers have already been procured before start of Yes/No concreting at site

22.

All cable trench work, backfilling and cable trench cover slabs have Yes/No been provided

23.

Earth mat work is complete

Yes/No

24.

Site is cleared from any construction material and power cables and Yes/No all T&P has been removed from site

25.

Microlevelling work is being done satisfactorily and the desired site Yes/No level is achieved

26.

Earth required for low lying area is being cut from high level areas

Yes/No

27.

Proper compaction of land as per specifications is being done

Yes/No

28.

Before micro levelling all foundations have been properly backfilled

Yes/No

29.

All metal/hard granite is properly stacked for recording

Yes/No

30.

Hard granite metal store of specified size is spreaded

Yes/No

31.

Metal is being brought from the selected/approved queries

Yes/No

32.

Proper level marks for spreading and measurement of metal have Yes/No been provided

33.

Metal spreading is completed and proper recording/measurements Yes/No have been taken

CHAPTER-3 SWITCHYARD EARTHING

___________________________________________________________________________ CHAPTER

THREE ___________________________________________________________________________ SWITCHYARD EARTHING Back to contents page

3.0

Introduction Back to contents page

The object of earthing is to maintain a low potential on any object. The purpose of a earthing system in a substation area is to limit the potential gradient within and immediately outside the area to a value, safe for the working personnel. Safety is to be ensured under normal as well as abnormal operating conditions. 3.1

Functional Requirements of Earthing System Back to contents page



To provide earth connection for the neutral points of transformer, reactor, capacitor banks, filter banks, generators.



To provide discharge path for lightning overvoltages coming via rod-gaps, surge arresters, shielding wires etc.



To provide low resistance path to earthing switch earthed terminals, so as to discharge the trapped charge to earth prior to maintenance or repairs.



To ensure safety of operating staff by limiting voltage gradient at ground level in the substation.



To provide a sufficiently low resistance path to earth to minimise the rise in earth potential with respect to a remote earth-fault. Persons touching any of the non-current carrying earthed parts shall not receive a dangerous shock during an earth fault. Each structure, transformer tank, body of equipment etc. should be connected to earthing mat by their own earth connection.

3.2

Earthing System in Switchyard Back to contents page

Following basic requirements are to be satisfied as so to ensure a proper and sound earthing system in substation switchyard. i)The earth resistance for the switchyard area should be lower than a certain limiting value “Ra” in order to ensure that a safe potential gradient is maintained in the

switchyard area and the protective relay equipments operate satisfactorily. For major switchyards and substations in India, this limiting value of earth resistance (Ra) is taken to be less than 0.5 ohm. ii)The grounding conductor material should be capable of carrying the maximum earth fault current without overheating and mechanical damage. The maximum fault level in the 400 KV system has been estimated to be 40 kA and this value of fault current is used in the design of earth mat for the 400 KV substation. iii)All metallic objects which do not carry current and installed in the substation such as structures, parts of electrical equipments, fences, armouring and sheaths of the low voltage power and control cables should be connected to the earthing electrode system. iv)Mechanical ruggedness of the ground conductor should be ensured. v)The design of ground conductor should take care such that whenever a fault occurs in substation, fault current flows through the faulty circuit to the connecting electrode. 3.3

Step and Touch Potential Back to contents page

Any person in the substation area is likely is encounter the following potential rises. i)The station earthing system should have earth resistance lower than 0.5 ohm for effective discharge of lightning over voltage to earth. ii)

Grounding mesh is provided below ground level. Earth electrodes are driven into ground at several points and are connected to the grounding mat to form Earthing Mesh. All the structures, transformer tanks, etc. are connected to this mesh.

3.3.1

Step potential Back to contents page

The potential difference between two steps of a person standing on the substation floor during the flow of earth fault current is known as step potential. 3.3.2

Touch potential Back to contents page

The potential difference between a step and the tip of the raised hand touching a substation structure during the flow of the earth fault current through the latter is known as touch potential.

The step potential and touch potential depend upon the following aspects: 

Earth fault current



Duration of earth fault



Whether short time (less than 3 sec.)



Whether sustained (more than 3 sec.)



Fault current flowing through body



Values of body resistance in the path

The design of grounding system should be such that the voltage gradient in volts/metre on the surface of the ground should be less than the permitted value. 3.4

Soil Resistivity Measurement Back to contents page

The earth resistivity is measured by driving 4 electrodes in ground in a straight line at equal spacing of 20-25m (Fig. 1). These electrodes are connected to terminals of an earth tester. A typical earth tester has 4 terminals C1, C2, P1 and P2. The electodes are connected to the tester in the order of C1, P1 and P2, C2. The handle of the tester is rotated in case of manual one or the button is pressed (in case of motorised tester) and the reading of the resistance is read on the megger scale. The reading of meggar is used in calculating the soil resistivity in Ohm-meters.

If R is the resistance measured then the Specific Resistivity = 2 aR where a= Distance between the electrodes The design of earth mat is based on the results of earth resistivity measured in the switchyard area. The earth resistivity is taken at about 15 places in switchyard and more particularly near shunt reactor, transformer, Circuit Breaker and control room locations. Prior to the testing of soil resistivity and earth resistance, site should refer to the guidelines issued by the Operation Services Deptt. at Corporate Centre. The operation manual of the testing instrument available at site should also be referred. Earthing Material

3.5

Back to contents page

Following Table gives the typical size and materials required for different earthing items in the substation: Table -1: Typical sizes of materials used for Switchyard Earthing Sl. No. 1.

Item

Size

Main Earthing Conductor to be buried 40 mm dia

Material Mild Steel rod

in ground (for earthed mat & earth pipes) 2.

Conductor above ground & earthing 75 x 12 mm leads (for equipment)

3. 4.

G.S. Flat

Conductor above ground & earthing 75x12 mm leads (for columns & aux. Structures)

Galvanised Steel Galvanised Steel

G.S. Flat

Earthing of indoor LT panels, Control 50 x 6 mm

Galvanised Steel

panels and out door marshalling G.S. Flat boxes, MOM boxes, junction boxes & lighting panels etc. 5.

Rod Earth Electrode

40 mm dia

Mild Steel

3000 mm long 6.

Pipe Earth Electrode (in treated earth 40 mm dia pit) as per IS.

3000 mm long

Galvanised Steel

7.

Earthing for motors

25 x 3 mm

Galvanised Steel

GS flat 8.

Earthing conductor along outdoor 50 x 6 mm cable trenches

3.6

Mild Steel

MS flat

Earthing Conductor Layout Back to contents page

i) Earthing conductor in outdoor areas is buried at least 600 mm below finished ground level or as specified. ii) Wherever earthing conductor crosses cable trenches, underground service ducts, pipes, tunnels, railway tracks etc. it is laid at minimum 300 mm below these and be re-routed in case it fouls with equipment/structure foundations etc. iii) Tap-connections from the earthing grid to the equipment/structure to be earthed are terminated on the earthing terminals of the equipment/structure as per earthing details. iv) Earthing conductors crossing the road is laid 300 mm below the road or at greater depth to suit the site conditions. v) Earthing conductors embedded in the concrete should have approximately 50 mm concrete cover. vi) Earth grid should be extended beyond 2000 mm from the switchyard fencing towards out side. vii) A minimum clearance of 1500 mm is maintained between the earthing conductor and the control room building. 3.7

Equipment and Structure Earthing in Substation Back to contents page

i)

Earthing pads are provided for the apparatus/equipments at accessible position. The connection between earthing pads and the earthing grid is made by two short earthing leads (one direct and another through the support structure) free from kinks and splices by 75 mm x 12 mm GS earth flat. The GS earth flat is welded to a MS Rod riser which is connected to the earth mat in ground.

ii)

All steel/RCC columns, metallic stairs etc. are connected to the nearby earthing grid conductor by two earthing leads. Electrical

continuity is ensured by bonding different sections of rails and metallic stairs. iii)

Metallic pipes, conduits and cable tray sections for cable installation are bonded to ensure electrical continuity and connected to earthing conductors at regular interval. Apart from intermediate connections, beginning points are also connected to earthing system.

iv)

A separate earthing conductor should be provided for earthing the lighting fixtures, receptacles, switches, junction boxes, lighting conduits etc.

v)

A continuous ground conductor of 16 SWG GI wire is run all along each conduit run and bonded at every 600 mm by not less than two turns of the same size of wires. The conductor is connected to each panel ground bus, all junction boxes, receptacles, lighting fixtures etc.

vi)

Railway tracks within switchyard are earthed at a spacing of 30 m and also at both ends.

vii)

50 mm x 6 mm MS (or of specified size) flat runs on the top tier and all along the cable trenches and the same is welded to each of the racks.

Further this flat is earthed at both ends

at an

interval of 30 mtrs. The M.S. flat is finally painted with two coats or Red oxide primer and two coats of Post Office red enamel paint or of specified material. viii) In isolator the base frame is connected to the earth mat. The following Table-2 gives the various parts required to be earthed alongwith their method of connection

Table:2 Details of Apparatus /Structures to be earthed in Switchyard Sl. No.

Apparatus

Parts to be

Method of connection

Earthed 1.

Support of bushing

Device flange or Connect the earthing bolt of the

insulators, Lightning

base plate

device to station earthing system.

Arrester, fuse, etc.

In the absence of earthing bolt or in case

of

conducting

connection

to

structures,

non-

connect

Earth terminal of device fastening bolts to earth each pole of 3 When the device is mounted on a phase

Surge steel structure, weld the structure,

Arrester

mounting the device flange; each supporting structure of apparatus to earthing

mesh

via

separate

conductor 2.

Cabinets of control and Frameworks of

Weld

the

framework

relay panels

switchgear and

separately

cabinets

cabinet minimum at two points to

mounted

of

each

board

and

the earth conductor of earthing system. 3.

High-voltage Breakers

4.

Isolator

Circuit Operating

Connect the earthing bolt on the

mechanism,

frame and to operating mechanism

frame

of CB to earthing system

Isolator

base Weld the

isolator

base

frame,

(frame),

connect it to the bolt on operating

operating

mechanism base plate and station

mechanism

earth.

bedplate.

Provide an auxiliary earth mat of 600 mm x 600 mm of earth conductors in the ground near the earth switch and connect the both.

5.

Surge Arrester

Lower point

earth To be directly connected to the earth mat.

6.

Potential

CVT

tank.

Transformer/CVT

neutral, winding

LV Connect the transformer earthing LV bolt to earthing system.

phase

lead

(if Connect LV neutral of phase lead

stipulated by the to 7.

Current Transformer

case

with

flexible

copper

designers)

conductor.

Secondary

Connect

winding and me

earthing bolt on transformer case

tal case

with a flexible copper conductor,

secondary

winding

to

the case being earthed in the same way as support insulators. 8.

Power transformer

Transformer

Connect

the

earthing

bolt

on

tank

transformer tank to station earth. Connect the Neutral directly to two dedicated earth pits.

9.

Fencing

Alternate

GS earth flat connects the fencing

Fencing portions to earth mat. 10.

Water tanks

Lightning

rods GS earth flat connects the lightning

provided

over rods to earth mat.

the top of water tank 11.

Cable trays & supports

Cable trays and GS flat running near trays is welded support

at a spacing of 750 mm and connected to earth mat at about 30 m distance.

12.

Shunt Reactor

Tank

Same as in transformer. NGR is also connected to two earth pits.

3.8

Jointing Back to contents page

i)Earthing connections with equipment earthing pads are bolted type. Two bolts are provided for making each connection. Equipment bolted connections, after being checked and tested are painted with anti-corrosive paint/compound of specified material.

ii)Resistance of Joint should not be more than the resistance of the equivalent length of the conductor. iii)All ground connections are made by electric arc welding. All welded joints are allowed to cool down gradually to atmospheric temperature before putting any load on it. Artificial cooling is not allowed. iv)Each earthing lead from the neutral of the power transformer/reactor is directly connected to two pipe electrodes in treated earth pit (as per IS) which in turn, are buried in Cement Concrete pit with a cast iron cover hinged to a cast iron frame to have an access to the joints. All accessories associated with transformer/reactor like cooling banks, radiators etc. are connected to the earthing grid at minimum two points. v)Earthing terminals of each lightning arrester & Capacitor Voltage Transformer is directly connected to rod earth electrode which in turn is connected to station earthing grid. 3.9

Measurement of Earth Resistance Back to contents page

Three electrode methods is used for measuring the earth resistance in switchyard (Fig. 14). To measure the earth resistance both C1 and P1 terminals of megger could be connected to a spike that is driven in ground and connected to earth mat whereas terminals P2 and C2 are connected to the equidistant spikes driven in ground (not connected to earth mat). The value of of R could be read in the scale with the rotation of the handle of megger or press of a button. This will give the value of earth resistance. The value as far as possible should be below 1 ohm. In case this value is high water should be sprinkled in the earthing pits for improvement of earth resistance.

DO’S DON’TS & SPECIAL PRECAUTIONS

3.10

Do’s Don’ts and Special Precautions Back to contents page

i) Metallic conduits should not be used as earth continuity conductor. ii) Wherever earthing conductor crosses or runs along metallic structures such as gas, water, steam conduits, etc. and steel reinforcement in concrete it should be bonded to the same. iii) Flexible earthing connectors should be provided for the moving parts. iv) Steel to copper connections should be brazed type and treated to prevent moisture ingression. v) Sheath and armour of single core power cables should be earthed at switchgear end and equipment side. vi) Contact surface of earthing pads for jointing free from scale, paint, enamel, grease, rust or dirt. vii) Earthing conductors or leads along their run on cable trench ladder, columns, beams, walls etc. should

be supported by suitable

welding/cleating at intervals of 750 mm/ as specified. viii)Light poles, junction boxes on the poles, cable and cable boxes/glands, lockout switches etc. are connected to the earthing conductor running alongwith the supply cable which inturn is connected to earthing grid conductor at a minimum two points whether specifically shown or not ix) Earthing conductor is generally buried 2000 mm outside the switchyard fence.

All the gates and every alternate post of the

fence is be connected to earthing grid. x) Meggar used for measuring soil resistivity should be calibrated with great accuracy. In case if an accurately calibrated meggar is not available, 2 or 3 different meggars should be used to take same set of readings. xi) The earth resistivity should be taken in dry weather condition. xii) For transformer & shunt reactor earthing, earth pits of 3-4 m depth below the ground with 40 mm dia GI pipe & specified quantity of salt and coke should be provided.

xiii)The earth resistance should also be measured after completion of laying of earth mat and earth electrodes by the same 4 electrode methods for complete system, individual earth pits & earth rod electrodes. xiv)The measured value of combined earth resistance should not be more than 0.5 ohm. xv) For earth electrodes and individual earth pits, this value can be upto 1 ohm. xvi)In case these values are not being achieved water should be poured in earth pits to bring the earth resistance within the specified range.

CHECK FORMAT

3.11

Check Format Back to contents page

1.

Proper unloading arrangement has been made at site Yes/No (Preferably with crane) to unload the material.

2.

All items have been checked with the packing list, MICC, Yes/No Challans, GR etc.

3.

After unloading the visual inspection of the materials has Yes/No been carried out along with the erection contractor.

4.

Earthing material has been checked for dimensions and Yes/No quality .

5.

The galvanization of steel (where GI steel is to be used) is Yes/No proper.

6.

Earthing conductor is buried at least 600 mm below finished Yes/No ground level/ at specified level.

7.

Earthing Conductor crossing the road is laid 300 mm below Yes/No the road or at greater depth depending on the site conditions

8.

Earthing conductor in outdoor areas is buried at least 600 Yes/No mm below furnished ground level.

9.

Earth grid has been extended beyond 2000 mm from the Yes/No switchyard fencing towards outside.

10

Earthing pads have been provided for the apparatus / Yes/No equipments at accessible position.

11

All steel/RCC columns, metallic stairs are connected to Yes/No nearby earthing grid conductor by two earthing leads.

12

Metallic pipes, conducts and cable tray sections for cable Yes/No installations are bonded & then connected to earthing conductor at regular interval

13

Earthing of Lighting fixtures, receptacles, switches, junction Yes/No boxes lighting conduit has been done by a separate earthing conductor.

14

Railway tracks within switchyard area has been earthed at a Yes/No spacing of 30m/specified distance and also at both the ends.

15

Cable trays have been connected to earthing flat of 50 mm Yes/No x 6 mm/ specified sized earthing flat.

16

This earth flat is earthed at about 30m distance.

Yes/No

17

Bolted conditions of earthing with the equipments have Yes/No been checked and tested before painting with anti corrosive paint.

18

For transformer and shunt reactor earthing, earth pits of 3-4 Yes/No m depth with specified sized GI pipe & specified quantity of salt and coke have been provided.

19

Sheath & armour for single core power cable have been Yes/No earthed at switchgear end.

20

All accessories in transformer and reactor like radiators Yes/No tank, cooling banks etc. are connected to the earthing grid at minimum two points.

21

Megger used for measuring earth resistivity has been Yes/No calibrated with great accuracy

22

Earth resistance has been measured after laying the Yes/No earthmat.

23

4 electrode method has been applied to measure the earth Yes/No resistance

24

Measured value of earth resistance is within specified range

25

In case the values are not within the specified limit, water Yes/No has been poured in earth pits to bring the earth resistance within the specified range

Yes/No

CHAPTER-4 SWITCHYARD STRUCTURES

___________________________________________________________________________ CHAPTER

FOUR ___________________________________________________________________________ SWITCHYARD STRUCTURES Back to contents page 4.0

Introduction Back to contents page

Two types of structures are used in switchyard erection. These are lattice type and pipe type structures. With both these type of structures, supply of other components like washers, fasteners, foundation bolts and other bolts & nuts is also linked up. Efforts should be made such that a proper co-ordination is made in procuring these supplies and structures so that erection work is not delayed due to non availability of one or the other item. Various aspects right from the scope of work to the erection of structures are described below. 4.1

Structure works in Substation Switchyard Back to contents page

The scope of structural work in switchyard generally includes receipt, handling, storage and erection of all lattice/pipe structures, lightning masts, beams as shown in structural arrangement drawings and lattice support for gantry and various equipments like CT, CVT, LAs etc. The structure supports also include the cap and base plates, stiffeners, clamps, foundation bolts mounting stool and bolts, fixtures for supporting operating mechanism boxes, control cabinet etc. It also includes the fabrication, supply, painting, erection of angle supports and embedding in cable trenches as per cable trench designs and layout, no. plates, phase plates and danger plates.

4.2

Receipt of Material & Inspection Back to contents page

After receipt of all the materials at site, it should be inspected jointly with the erection agency. This inspection is required to check the materials received for their quantity, quality, correctness and identification marks as per the delivery challan/ packing list etc. One should go for checking the following :i)

Despatch documents such as RR, LR, GR, MICC, Gate Pass, Packing List etc.

ii)

Quantity of materials received with the delivery challan, packing list, BOQ and any shortages should be recorded.

iii)

Identification marks should be checked from the MICC.

iv)

Any physical damage should be brought to the notice of supplier.

4.3

Storage Back to contents page

i)

The erection agency is allowed to store the angle/pipe material near the place where tower gantries are to be installed. All angles and pipes are to be stacked properly in such a way that retrieving of required materials is easy.

ii)

Maintenance of proper stock registers by the erection agency is to be checked regularly by duly counter signing the registers.

iii)

Bolts/nuts, spring washers, pack washers (in bags) should be stored in the allocated room/building meant for storage with the proper tags depicting the size, quantity, code no., supplier name etc.

iv)

In case the store building is not ready, the material may be kept tents with adequate security.

4.4

Erection Back to contents page

4.4.1

Erection of Gantry & Lattice Structures Back to contents page

i) The erection should be carried out as per the specified technical instructions and approved drawings. ii) Tolerances are established in the approved manufacture drawings or as stipulated in the technical specifications. Necessary care should be exercised in handling to avoid the distortion of structures, the marring of finish or bending of tower members. iii) The erection work is carried out manually (by built up or piece meal method) using ginpoles/derricks. However, crane can be used for this purpose. iv) The members are kept on ground serially according to erection sequence. v) The erection progress from the bottom upwards. vi) The cross braces of the first section which are already assembled on the ground are raised one by one as a unit and bolted to the already erected corner leg angles. vii) For assembling the second section of the towers, gin poles are placed one each on the top of the diagonally opposite corner legs. These two poles are used for raising parts of second sections. viii)This process is continued till the complete tower in gantry is erected.

ix) The lattice structure are used for various equipment erection in the switchyard like circuit breaker, current transformer, CVT and surge arrester. x) Proper care in horizontal levelling of these lattice structure is taken by using water level/spirit level. Even dumpy level/theodolyte may also be used for good accuracy. xi) To maintain the proper level necessary shims are inserted in pipe works. xii) The beam erection work of tower is carried out at the ground by assembling various members preferably in two parts. xiii)The assembled beam is lifted either by crane or by chain pulley block. Even winch machines can also be used for this purpose. xiv)The assembled beam is lifted slowly and carefully. xv) One side of the beam is tightened first with the gantry structure on one side. For finer adjustments winch machines can be used. This side of assembled beam is fixed to the tower by proper sized bolts, nuts & washers. xvi)All the support structure for various equipments should be levelled horizontally with water/spirit levels. 4.4.2

Erection of Pipe Structure Back to contents page

i) The pipe structure are placed on the foundation bolts preferably by cranes. ii) During erection the top level of the pipe structure should be maintained horizontal.

iii) This can be checked with the spirit level and shims can be used to fill up the gap and to maintain the proper horizontal level. iv) Necessary care is taken during pipe structure erection so that no damage is caused to the threads of the foundation bolts. v) The persons doing erection of pipe structure should use the safety measures like helmets and safety belts etc. 4.3

Lightning Masts Back to contents page

Lightning masts are the highest angle iron structures in the switchyard. These are designed in the switchyard keeping in view the approved switchyard bays. The erection procedure of Lightning Masts is similar to that of tower and gantries.

DO’S DON’TS & SPECIAL PRECAUTIONS

4.4

Do’s, Don’ts and Special Precautions Back to contents page

During the erection of gantries/lattice structures/pipes following points should be kept in mind. i) As the supplies of lattice structure, washers, bolts and nuts, pipes etc. is in the scope of different agencies, a co-ordinated follow up should be maintained with the suppliers to the deliveries of these items as per schedule. This will help in avoiding delays of erection works due to non availability of one of these items. ii) The lattice members, pipes etc. should be checked as per the BOQ at site. The shortage or missed members in supplies should be taken up with the suppliers rigorously. The erection work should be started only after the structures are complete memberwise. iii) Cranes should be used preferably for erection of pipe structure in the switchyard. iv) All safety procedures for erection work like use of safety helmets, safety belts, use of guy wires etc. should be strictly adhered to during structure erection works in the switchyard. v) All the net/bolts should be tightened properly after the completion of structure erection. vi) Punching of bolts should be done. vii) Any bend members and pipes should not be allowed and straightaway rejected during supply stage. viii)No hammering of members should be allowed to match the holes during erection work.

ix) 2-3 threads of bolts should be exposed after tightening the nuts for punching purpose. x) Proper sized/bolts/nuts and pack washers should be used in erection. xi) After the completion of tower erection, proper tightening is to be done. Before carrying out the final punching it must be ensured that proper sized spring washers are provided. xii) During erection, it should be seen that brazings should be properly erected i.e., outer face of the member should always be at top so that water does not stager on the members (water gate). Also, members should not be over tensioned while carrying out the erection. xiii)Proper lifting arrangement of 4-5 MT capacity should be used during erection works. xiv)Proper sized spanners (box and ring type) as well as DE spanners should be used. xv) Poly-propylene ropes of 18/20/25 mm dia of about 100 m/as per requirement length each may be used. The ropes should be checked before use so as to avoid any breakage during works. xvi)Steel rope of 3/8” dia of required length should be used with winch machine. xvii)D-shackles of 2 to 20 MT of different sizes should be used. xviii)Single sheave and double sheave pulleys should not be less than 5 MT capacity. These should be checked for their smooth rotation and locked during use on works.

xix)The verticality of different lattice structures should not be less than the specified tolerance of 1 in 360. xx) Proper punching of bolts/nuts is to be done on the various structures.

CHECK FORMAT

4.5

Check Format Back to contents page

1.

All items have been checked with the packing list, MICC, Yes/No Challans GR etc.

2.

After unloading the visual inspection of the angles/members Yes/No has been carried out for any bend/ damage.

3.

All the members have been stacked properly in store.

Yes/No

4.

Angles have been checked for size/dimensions, galvanization Yes/No and bend etc.

5.

Required quantities of washers, fasteners, foundation bolts & Yes/No other bolts/nuts are available before starting the structure erection at site.

6.

All pipes have been checked and found straight w.o. any bends Yes/No or damage.

7.

Bolts/nuts/spring, pack washers are stored in the closed room Yes/No (in bags).

8.

Proper tags depicting the size, quantity code no. and supplier Yes/No name etc. have been written/inscripted on the tags tied on the bags.

9.

During structure erection proper safety measures like helmets, Yes/No safety bolts, ropes etc. are being used by the working personnel.

10.

All lattice members are available (as per drawings) before start Yes/No of erection.

11.

Proper care in horizontal levelling of lattice structure for Yes/No equipments is taken by using water/spirit level.

12.

To maintain proper level, shims have been inserted in pipe Yes/No works.

13.

Assembled beam (of gantry structure) is being lifted with crane Yes/No for erection with proper safety.

14.

Tightening and punching of bolts has been done properly.

Yes/No

15.

Hammering of members has been disallowed during erection at Yes/No site.

16.

2-3 threads of bolts are exposed out after tightening the nuts for Yes/No punching purpose.

17.

Proper sized bolts/nuts and pack washers are used in tower Yes/No erections.

18.

Verticality of tower is within the safe tolerance of 1 in 360.

Yes/No

CHAPTER-5 BUSPOST INSULATORS & BUSBARS

___________________________________________________________________________ CHAPTER

FIVE ___________________________________________________________________________ BUS POST INSULATORS & BUS BARS Back to contents page

5.0

Introduction Back to contents page

The substation busbars can be broadly classified in the following three categories: i)

Outdoor Rigid Tubular Busbars

ii)

Outdoor flexible ACSR aluminium alloy busbars

iii)

Indoor busbars

The busbars are designed to carry certain normal current continuously. The cross-section of conductors is designed on the basis of rated normal current and permissible temperature rise. The value of cross section so obtained is verified for temperature rise under short-time short-circuit current. The busbar conductors are supported on post insulators or strain insulators. The insulators experience electro-dynamic forces during short circuit currents. These forces are maximum at the instant of peak of first major current loop. These forces produce bending moment on separated insulators. The spacing between adjacent insulators is decided on the basis of bending moment per metre and strength of insulators. 5.1

Steps in Busbar Design Back to contents page

The busbar design is carried out in the following steps: i) Choice of cross-section of conductor based on required normal current, given ambient temperature and specified permissible temperature rise. ii) Calculation of temperature rise under short time current to see that it is in safe limits.

iii) Calculation of electro-dynamic forces per metre for given short circuit current. iv) Calculation of choice of support insulators on the basis of bending moment withstand value. v) Calculation of span of support insulators on the basis of the force, bending strength of insulators and factor of safety. vi) Design of insulator system, phase to phase clearance, phase to ground clearance and creepage. vii) Design of support structures. viii)Design of clamps and connectors, flexible joints. 5.2

Forms of Busbars Back to contents page

Busbars of Outdoor Switchyard are in the following forms: 

ACSR conductors supported at each end on strain insulators.



Tubular Aluminium Conductors supported on post insulators made of porcelain. These are either welded to get extended lengths.



Busbars for Indoor Switchgear are in the form of aluminium or copper flats. These are supported on epoxy cast insulators.

5.2.1

ACSR Back to contents page

ACSR conductor to be used for busbars is supported on insulators. As most of the equipments can be installed below the flexible bus, land requirements are also less. The cost of this scheme is lower due to less no. of support structures. 5.2.2

Aluminium Back to contents page

Aluminium is used for busbars in indoor and outdoor switchgear. Aluminium and aluminium castings (5 to 12% silicon) are used in busbar. Aluminium is used in the form of strips /rectangular bars for busbar application. While using aluminium for busbars, the difficulties arise due to the following aspects: i) Higher resistivity, hence associated problems of temperature rise. ii) Lower tensile strength than copper. iii) Lower thermal conductivity than copper.

iv) Higher coefficient of linear expansion than copper. v) Higher joint resistance and associated problems about joining. vi) Special welding techniques are necessary. Configuration of Busbars in Outdoor Substation

5.3

Back to contents page

The conductors of a busbars systems in an outdoor substation are of the following two types: i) Rigid aluminium tubular bus conductors supported on post insulators ii) Flexible ACSR supported on strain insulators. The conductors of three phases of each bus are placed in horizontal configuration. Table 1: Comparison between Rigid Bus System and Flexible Bus System Feature

Rigid Bus System

Cost

Higher because

Flexible Bus System of higher

Lower

conductor cost, post insulator cost Land Area

Larger

requirement

Lower. Most of the equipment installed below the flexible bus

Number of support

- More numbers

- Less numbers

structures

- Simple

- Complex

- Amount of steel lesser 5.4

Receipt and Inspection of Material at site Back to contents page

i) The items should be checked with the packing list, MICC, Challans GR etc. ii) In case of any discrepancy from the above documents/LOA the same may be intimated to the manufacturer at the earliest. iii) Any type of damage to the panels during transportation or any missing items should also be brought to the notice of the panel supplier. iv) All materials and packages are to be carefully opened and verified for damages and shortages, if any. These shortcomings have to be

properly intimated to the manufacturer as well as to the Insurance authorities as the case may be. v) Handling of large crates should be handled by crane carefully. vi) All items should be stored on ramps/platforms, free from water logging. vii) BPIs are to be stored separately to avoid breakages. 5.5

Bus Post Insulators Back to contents page

Post type consist of a porcelain part permanently secured in a metal base to be mounted on the supporting structures. 

They are capable of being mounted upright. They are designed to withstand any shocks to which they may be subjected to by the operation of the associated equipment.



Porcelain used is homogeneous, free from lamination, cavities and other flaws or imperfections that might affect the mechanical or dielectric quality and thoroughly vitrified, tough and impervious to moisture. Glazing of the porcelain is of uniform brown in colour, free from blisters, burrs and other similar defects.



The insulator have alternate long and short sheds with aerodynamic profile.



The design of the insulators should be such that stresses due to expansion and contraction in any part of the insulator should not lead to deterioration in Bus Post insulators

i)

Every bolt should be provided with a steel washer under the nut so that part of the threaded portion of the bolts is within the thickness of the parts bolted together.

ii)

Flat washer should be circular of a diameter 2.5 times that of bolt and of suitable thickness. Where bolt heads/nuts bear upon the levelled surfaces they are provided with square tapered washers of suitable thickness to afford a seating square with the axis of the bolt.

iii)

All bolts and nuts should be made up of steel with well formed hexagonal heads forged from the solid and hot dip galvanised. The nuts should be good fit on the bolts and two clear threads

should show through the nut when it has been finally tightened up. 5.5.1

Technical Parameters of typical Bus Post Insulators are Back to contents page

a)

Type

Solid core

Solid core

b)

Voltage class (kV)

420

245

c)

Dry and wet one minute

680

460

+ 1425

+ 1050

power frequency withstand voltage, Kv (rms) d)

Dry lightning impulse withstand voltage

e)

Wet switching surge

+ 1050

-

withstand voltage (kVp) f)

Max. radio interference

1000

1000

320 (Min.)

156 (Min.)

800

800

voltage (in microvolts) at voltage of 305 kV (rms) and 156 (rms) for 400 kV & 220 kV respectively between phase to ground. g)

Corona extinction voltage (kV rms)

h)

Total minimum cantilever strength (Kg)

i)

Minimum torsional moment

As per IEC-273

j)

Total height of insulator (mm)

3650

2300

k)

P.C.D Top (mm)

127

127

Bottom (mm)

300

254

Top

4

4

Bottom

8

8

Top

M16

M16

Bottom dia

18

18

Pollution level as per

Heavy(III)

Heavy(III)

l)

m)

n)

No. of bolts

Diameter of bolt/holes (mm)

IEC-815 o)

Minimum total creepage

10500

6125

distance for Heavy Pollution (mm) 5.6

Erection of Aluminium Bus Bar Back to contents page

i) Before erection of the tube, it is to be checked for any scratches. If any scratches are observed, they are to be repaired by means of smooth file and emery paper. ii) As Aluminium tube is soft material it is to be handled carefully to avoid damages and scratches. iii) The tube can be erected by means of crane or by means of a derrick. iv) Only polypropylene ropes are to be used to tie the tube while lifting. v) After erection of the Aluminium tube it is to be checked that it rests on all the BPI clamps (rigid/sliding/expansion) properly.

If not,

necessary adjustments may be made by providing shims between the clamp and the BPI. vi) During erection of the tube care should be taken such that the tube should be in perfect straight line and perfect level. The BPI clamps suitable for Aluminium tube (rigid/sliding/expansion types) are erected as per the erection key diagram. 5.6.1

Bending Procedure of Aluminium Tube During Erection: Back to contents page

Following bending procedure should be adopted during bending of the Aluminium tube while bus bar erection i) Wherever required the tube is bent suitably into a Z shape. ii) Suitable tube bending machine is to be made use of. iii)

The tube bend should not be bent more than 45o.

iv) To ensure the circular cross section of the tube at the place of bending the tube should be filled with smooth sand, well compacted throughout the length of the tube and the ends should be plugged.. v) Care should be taken such that the tube is in one plane only even after bending. 5.6.2

Welding of Aluminium Tube:

Back to contents page

i)

Aluminium tube welding is done at erection site only by a qualified and approved welder.

ii)

Tube ends to be welded are cut neatly and precisely in shape.

iii)

Both the tubes to be welded are kept in a plane and in the same axis.

iv)

Plane of the cut edge is to be exactly perpendicular to the plane of longitudinal section of the tube.

v)

The edge is to be made by grinding to the shape.

vi)

Tube centring spacer is inserted in between them.

vii)

Suitable welding sleeves of specified length for the above tube, specially supplied for the purpose of tube welding is kept within the tube, equally distributed in length among the tubes.

viii) After putting the pieces and welding sleeve in position 12 mm dia holes are to be drilled at 100 mm intervals. ix)

Aluminium rods of specified length and dia with one end counter shunk are inserted through these holes.

x)

To accommodate the counter shunk aluminium rod the counter shunk shape is drilled in the Aluminium Tube only.

xi)

After positioning the tubes, welding sleeve and the Aluminium rods in position the welding is to be taken up.

xii)

The counter shunk Aluminium rods also are to be welded to the tube.

xiii) Milli volt drop tests for testing the joints should be performed in the field. xiv) All other tests as given in the FQP should also be performed. xv)

If any of the joints are not successful in the test, those joints are to be re-done.

5.7

Welding Procedure and Welder’s Qualifications Back to contents page

The erection contractor is supposed to get the Welding Procedure and Welder’s /Welding Operator’s Qualifications approved from the Corporate QA deptt. (in the enclosed proforma at Annexure-I and Annexure-II) before commencement of the Aluminium welding of the bus at site.

DO’S DON’TS & SPECIAL PRECAUTIONS

5.8

Do’s, Don’ts and Special Precautions Back to contents page

i)In Aluminium tube the welding joint should not be at the centre. It should be between support and 1/3 distance of the span. ii)Dust free atmosphere is to be maintained at the place of welding. iii)Check that proper alignment for complete aluminium tube is achieved and verified before any welding is done. iv)The welds in the Aluminium tube should be kept to the minimum and there should not be more than one joint in the tube in any span length. v)No inflammable material should be present around the work spot. vi)While welding work is under progress, ensure the argon gas flow along with the arc and also as long as the weld metal is red hot. This is to prevent oxidation of the weld metal because of exposure to oxygen in the atmosphere. vii)The shed profile should meet requirements of IEC-88815 for the specified pollution level. viii) Welding of Aluminium tube at site should be done by adopting an approved welding procedure and employing a qualified welder. ix) Welders

employed

for

Aluminium tube welding should be

experienced one in the field. x)Corona bells should be provided wherever the bus extends beyond the clamps and on free ends, for sealing the ends of the tubular conductor against rain and moisture and to reduce the electrostatic discharge loss at the end points.

5.9

Check Format Back to contents page

1.

Proper unloading arrangement has been made at site (Preferably Yes/No with crane) to unload the packages.

2.

All items have been checked with the packing list, MICC, Challans Yes/No GR etc.

3.

After unloading the visual inspection of the packings has been Yes/No carried out along with the erection contractor and preferably with

CHECK FORMAT

the manufacturer of the equipment. 4.

Any type of damage to the equipments/components during Yes/No transportation or any missing items has been brought to the notice of the supplier.

5.

Porcelain of BPI is free from lamination, cavities and other flaws Yes/No or imperfections.

6.

Glazing of the Porcelain is uniform and free from blisters, burrs Yes/No and other defects.

7.

Every bolt has been provided with a steel washer under the nut.

Yes/No

8.

Packed washers of suitable size and thickness have been Yes/No provided.

9.

Aluminium tube welding is being done by a qualified welder.

Yes/No

10.

Aluminium tube welding is done as per approved welding Yes/No procedure.

11.

Dust free atmosphere has been maintained at the place of Yes/No welding.

12.

No inflammable material is present around the work spot

Yes/No

13.

Care is taken so that not more than one joint is provided in one Yes/No span length

14.

Aluminium tube has been checked for any scratches

Yes/No

15.

In case of any scratches these have been repaired by mean of Yes/No smooth file and emery paper.

16.

Only polypropylene rope is being used for Aluminium Tube

Yes/No

erection. 17.

The tube is in the straight line and perfectly levelled.

Yes/No

18.

BPI clamps for holding Aluminium tube have been erected as per

Yes/No

erection key diagram.

19.

Suitable bending machine is used for bending purpose.

Yes/No

20.

Care has been taken to maintain circular cross section of tube at Yes/No the place of bending by filling tube with smooth sand, well compacted in the entire length & ends plugged.

21.

Care has been taken so that pipe is in one plane after bending.

Yes/No

Annexure - I QW-482 WELDING PROCEDURE SPECIFICATION (WPS) SECTION IX, ASME-1986 _____________________________________________________________ Joints (QW-402) Joint Design : Backing

:

_____________________________________________________________ Base Metals (QW-403) P.No. 23, Group No. SB221 to P No. 23, Group No. SB 221 Specification type and grade

:

Pipe dia range

:

Thickness Range

:

_____________________________________________________________ Filler Metals (QW-404) F. No. 23 Specification No. : (SFA) 5.10 AWS No. ER 4043 Size of filler metals : _____________________________________________________________ _____________________________________________________________ Positions (QW-405) Position of groove

:

Welding progression

:

_____________________________________________________________ Preheat (QW-406) Preheat temperature min. Interpass temperature max. Preheat maintenance _____________________________________________________________ Post weld heat treatment (QW-407) Temperature range Time range

____________________________________________________________ Gas (QW-408) Shielding gas Percent composition (mixture) Flow rate Gas backing Trailing Shielding gas composition _____________________________________________________________ _____________________________________________________________ Electrical characteristics Current AC or DC Amps (Range) Tungston electrode size and type Mode of metal transfer for GMAW Electrode wire feed speed range _____________________________________________________________ Technique (QW-410) String or weave bead Orifice or gas cup size Initial and interpass cleaning Method of back gauging Oscillation Contact tube to work distance Multiple or single pass (per side) Multiple or single electrode Travel Speed (Range) Peening Other _________________________________________________________________ Weld

Process

Filler Class

Metal dia

Current

Voltage

Others Layer

Range Type

Amp

Polar

Range

Travel Speed

Annexure - II DATA - FORMS

QW-484 SUGGESTED FORMAT FOR MANUFACTURER’S RECORD OF WELDER OR WELDING OPERATOR QUALIFICATION TESTS Welder Name _________________

Check No. __________ Stamp No. _______

Welding Process __________________ Type ______________________________ In accordance with Welding Procedure Specification (WPS) ___________________ Backing (QW-402) ___________________________ Material (QW-403) Spec. ______ To ______ Thickness _______

of P.No. ______ to P.No. ________ Dia _______

Filter Metal (QW-404) Spec. No. _________ Glass No. _________F No. _________ Other _____________________________ Position (QW-405) (1G, 2G, 6G) ________________________________________ Gas (QW 408) Type _______________ % Composition _____________________ Electrical Characteristics (QW 409) Current _________________ Polarity _______ Weld Progression (QW-410) __________________________________________

Other _____________________________________________________ For Information Only Filler Metal Diameter and Trade Name _________________________ Submerged Arc Flux Trade Name _________________________ Gas Metal Arc Welding Shield Gas Trade Name _______________________

Guided Bend Test Results QW-462.2(a). QW-463.2(a),QW-462.3(b) Type and Fig No.

Radiography Test for

(QW 304 & QW-305)

For alternative ____________ in above welds by radiography Radiographic Results _________________________ Filler Weld Test Results _____________________62.4(a), QW-462 4(b) Fracture Test (describe the location, nature _________________________ Length and Percent of _________________ inches

%

Macro Test-Fusion Appearance -Fillet Size________________________ in Convexity in or Concavity _________ in ______________ Test conducted by ____________________ Laboratory - Test No. _______ We certify that the statements in this record are correct and that the test welds were prepared, welded and tested required by the Code.) NOTE: Any essential variables in addition to those above shall be recorded.

CHAPTER-6 STRINGING SWITCHYARD

___________________________________________________________________________ CHAPTER

SIX ___________________________________________________________________________ STRINGING IN SWITCHYARD Back to contents page

6.0

Introduction Back to contents page

In switchyard overhead stringing work is done between the gantries and from the last tower on the lines to the first gantry structure. The overhead stringing in 400 KV yard is done with twin ACSR moose conductor. Erection of equipments can be started only after the overhead stringing has been completed in the gantries of the switchyard. The various outdoor equipments are connected with overhead conductors by jumpers/droppers with suitable clamps. Stringing is done manually in the switchyard, however, winch machines may be used for final sag. 6.1

Pre- Stringing checks Back to contents page

Though stringing work in switchyard is of small nature as compared to a transmission line even then the site should take care of the following before the stringing work starts at site. i) Before starting and also during stringing works the condition of conductor should be checked for any damage or scratches to the aluminium strands of conductor. ii) The glass/porcelain portion of insulators should be checked for any cracks

iii) Insulators should be clean from dust or other foreign materials. iv) Conductor should not be allowed to lie or rub on the ground during paying/pulling. v) Nuts and bolts of all gantry structure should be checked and the tower members should be complete in all respect. 6.2

Stringing Back to contents page

The process of manual stringing of moose conductor at site involves the following steps : i) Conductor is pulled between the gantries and strung on the suspension on insulator strings. ii) The final sagging is done by using winch machines. The winch machines are connected to the leg of the towers/gantries. iii) Final adjustment of conductor is done upto the desired point that point by moving the conductor through winch machines and the conductor is cut at the desired length. iv) Dead end joint by compression machines is provided at the end of the conductor with the dead end cone compressed with compression machine. v) Conductor is strung at the end with the double tension fitting. vi) On

suspension

structure

the

conductor

is

strung

through

suspension clamps. vii) Spacers are provided between twin conductors after final sag is completed. 6.3

T & P and Materials used for Stringing Back to contents page

The following Tools and Plants and Line material is required while stringing in substation switchyard.  Single sheave pulley (open type)

-

4 Nos.

 Double sheave pulley

-

2 Nos.

-

1 No.

 Winch machine 10T capacity

-

1 No.

 Come along Clamp(Bolted/Automatic

-

6 Nos.

 Wire Cutter

-

1 No.

 Poly-propylene rope (25 mm dia)

-

100 m or as

 Hydraulic/manual compression machine of 100T capacity with die sets

desired  D -Shackle

-

8 nos.fs

 Wire slings of required length

-

16 mm dia

 Spanners, round/flat files Screw driver,

-

1 set

flat files, steel tape, Hecksaw frame

each

& blades / as per reqmt.  ACSR moose conductor

-

As per

-

- do

-

- do

-

- do

reqmt.  Single suspension fittings  Double tension fittings  120 kN porcelain/glass insulators for suspension fitting -

 160 kN porcelain/glass insulators for tension fitting

-

-

-

-

do  Spacers (Bundle spaces and/or Rigid spacers) do -

DO’S DON’TS & SPECIAL PRECAUTIONS

6.4

Do’s Dont’s and Special Precautions Back to contents page

i) Conductor during stringing should not be allowed to drag on ground. For this purpose wooden planks or ground rollers should be used to avoid any damage to the conductor. ii) Insulator string should be pulled in such a way that it does not drag/entangle with the tower members causing any damage. iii) Adequate safety precautions should be taken by the personnel working on the towers/ground. They should wear safety helmets and use safety belts whole working on towers/structures. Workers and supervisory staff working on ground should wear the safety helmets. iv) Conductor should be checked constantly as it is unwound from conductor drum for any broken, damaged or loose strand. In case if any major defect is noticed the defective conductor has to be removed. v) Marking of conductor should be done correctly after adjusting length of tension fitting. vi) Conductor should be cut at the marked point and dead end joint be provided. vii) Sag should be checked by sighting through the theodolite placed on ground near the tower. Any mismatch should be corrected by using sag adjustment plate in tension fitting. viii)Immediate medical care should be provided to workmen met with an accident. First Aid Box should be available at stringing site. ix) Insulators should be completely cleaned with soft and clean cloth.

x) It should be verified that there is no crack or any other damage to insulators. xi) It is very important to ensure that ‘R’ clips in insulator caps are fixed properly. This is a security measure to avoid disconnection of insulator discs. xii) Necessary precautions should be taken so that no damage to insulators is caused during hoisting. In case of any damage, the same needs to be replaced. xiii)All hardware fittings should be provided as per approved drawings. xiv)It should be verified that all nuts and bolts are tightened properly. xv) It should be ensured that all the necessary security pins (split pins) are fixed properly. xvi)Conductor should be rejected in case it is found to contain any broken, damaged or loose strands. xvii)Proper arrangements should be made to avoid rubbing of conductors on ground/hard surfaces by providing wooden planks. xviii)Subconductors of each phase should be simultaneously tightened by winch machine fixed on tower leg until the desired final sag is achieved. xix)Marking of conductor should be done correctly after adjusting length of tension fittings. xx) Conductor should be cut at the marked point and dead end joint be provided with adequate compressive strength. xxi)Spacers should be provided as per approved placement chart. xxii)Length of jumper should be carefully checked such that it is in parabolic shape and jumper drop is as per approved drawing.

Length of jumpers of sub-conductors of a bundle should be properly checked so that jumper spacers lie in horizontal position as far as possible. xxiii)All nuts and bolts of jumper fittings should be properly tightened. This is very essential to ensure tightness of jumpers to avoid hot spot and melting in future. xxiv)Jumper spacers should be provided as per technical specification and approved drawings. xxv)No damaged component of any hardware fitting should be used on works. xxvi)Sag mismatch should be within permissible limits. xxvii)All fittings provided should be as per specification and approved drawings. All necessary details like make, dimension, size and specifications of these fittings should be recorded separately in register for tractability in future. xxviii)Jumpers/drops

should

be

tightened

properly.

Live

metal

clearance should be maintained as per specification. xxix)Insulators should be cleaned with soft cloth. Glazing should be proper and there should be no crack or white spot on its surface. xxx)‘R’ Clips in insulators should be fitted properly. xxxi) All Nuts/Bolts in fittings should be tightened properly. xxxii)All components of fittings should be completely provided as per approved drawings. xxxiii)In case of Tension fitting dead end joint dimensions before and after compression should be checked and recorded.

xxxiv)All components of spacers/jumper spacers should be provided as per approved drawings.

6.5

CHECK Check Format

FORMAT Back to contents page

1.

Towers are tightened properly and all the members, Nut/Bolts Yes/No are complete in no. and size.

2.

All Line materials, tested T & P, safety equipments and Yes/No relevant drawings are available for stringing.

3.

Conductor

is

checked

continuously

during

stringing

in Yes/No

switchyard. Damaged portion, if any, is removed. 4.

Proper arrangements are made to avoid rubbing of conductor Yes/No on ground/hard surfaces.

5.

Sag is measured correctly at prevailing temperature. Details Yes/No are recorded.

6.

After measuring sag, marking/cutting of Earthwire/ conductor is Yes/No done correctly to fix dead end joint.

7.

Conductor, insulators and other hardware fittings are available Yes/No at site before starting the overhead stringing.

8.

Insulators and other hardware fittings have been cleaned Yes/No properly before erection

9.

All fittings have been assembled at ground and all components Yes/No are OK.

10.

All components of fittings have been checked up for Yes/No dimensions and make as per the manufacturer’s drawings

11.

Insulators have been checked for any cracks/damage and care Yes/No has been taken that insulators are not broken during lifting.

12.

Care has been taken so that conductor while pulling is not Yes/No damaged.

13.

Proper sag and tension have been maintained as per the day Yes/No temperature and sag tension chart

14.

Subconductors

of

each

phase

are

being

tightened Yes/No

simultaneously by winch machine & to achieve the desired sag. 15.

All nuts & bolts of jumper fittings have been tightened properly.

Yes/No

16.

Jumper spacers have been provided.

Yes/No

17.

Spacers have been provided as per the spacer placement Yes/No chart.

18.

Care has been taken to avoid any overtensioning.

Yes/No

19.

R. Clips of the insulators in insulator string have been properly Yes/No provided.

20.

In both suspension and double tension fitting the split pin have Yes/No been splitted properly.

21.

Length of jumpers has been measured properly to give it a Yes/No parabolic shape.

22.

In case of tension fitting dead end joint dimensions before & Yes/No after the compression are checked and recorded.

23.

Jumpers are tightened properly. Live metal clearance have Yes/No been maintained as per specification.

CHAPTER-7 SURGE ARRESTER

___________________________________________________________________ CHAPTER

SEVEN SURGE ARRESTER Back to contents page

7.0

Introduction Back to contents page Surge Arrester is a device designed to protect electrical equipments from high voltage surges and to limit the duration and amplitude of the follow current. Surge arresters are used to protect Power System Installations and equipments against lightning overvoltages also. Generally arresters are connected in parallel with the equipment to be protected, typically between phase and earth for three phase installations. The main element of a surge arrester is the ‘Non-Linear Resistor’, the part of the arrester which offers a low resistance to the flow of discharge current thus limiting the voltage across the arrester terminals and high resistance to power frequency voltage, thus limiting the magnitude of follow current. There are 2 types of designs available for EHV Surge-Arrester. These are Conventional gapped Surge-Arrester (Value Type) and Metal Oxide Surge-Arrester.

7.1 Conventional Gapped Lightning Arrester (Valve Type Arrester) Back to contents page In a substation the Surge Arrester is connected between line and earth. It is the first apparatus as seen from the overhead transmission line entering in the switchyard. It consists of resistor elements in series with gap elements offer non-linear resistance such that for normal frequency power system voltages the resistance is high however, for discharge currents the resistance is low. The gap units consist of air gaps of appropriate length. During normal voltage4s the lightning

arrester does not conduct. When a surge-wave travelling along the Overhead line comes to the arrester, the gap breaks down. The resistance offered being low the surge is diverted to the earth. After a few micro seconds the surge vanishes and normal power frequency voltage is set up across the arrester. The resistance offered by resistors to this voltage is very high. Therefore, are current reduces and voltage across the gap is no more sufficient to maintain the arc. Therefore, the current flowing to the earth is automatically interrupted and normal condition is restored. The high voltage surge is discharged to earth. Hence the insulation of equipment connected to the line is protected. 7.2 Metal Oxide Lightning Arresters Back to contents page The metal oxide arresters without spark gaps consist of an active part which is a highly non linear ceramic resistor made of essentially Zinc Oxide. Fine Zinc Oxide crystals are surrounded by other metal oxides (additives).

Such

microstructures

render

extreme

non-linear

characteristics to these ceramic resistors. In the operating characteristic of Surge Arrester the current axis is in logarithmic scale. The current increases by 107 orders of magnitude when the voltage across element doubles. This special characteristics is the heart of protection technology in this type of Surge Arrester. The lower linear part ‘A’ is temperature dependant and exhibits a negative temperature coefficient. The arrester is designed in such a way that the applied operating voltage gets located around point ‘O’. This results in a continuous resistive curent of few micro amps flowing through the resistor elements. Under over voltage condition, the voltage

increases

and

shifts

operating

pont

momentarily

for

overvoltage duration to point near ‘B’. This results in a resistive current of few milli-Amperes flowing through the resistor elements. As soon as the overvoltage disappears the operating point shifts back to ‘O’. In the event of transient switching or lightning vervoltages, the operating point will shift to portion ‘C’. For the transient of a few micro seconds it will draw current in the range of 5/10 k Amps. In the event of very high lightning current of the order of 40 to 100 k Amps peak, the operating

point will shift to portion ’D’. However, on expiry of transient of few milli seconds the operating point will come back to point ‘O’. Thus the operating point of these arresters is normally located at point ‘O’ called Maximum Continuous Operating Voltage (MCOV) and the point ‘B’ of the Fig. (5) indicates approximately the rated voltage of arrester. The arrester can stay at point ‘O’ i.e., MCOV, all long its life but can stay at point ‘B’ (fault condition), i.e. Rated Voltage, for only 10 seconds (it is presumed that system breakers will operate to isolate the fault within 2 seconds). The energy that gets dissipated, I.e. (I2R) during continuous or overvoltage condition decides the size (dia) of ZnO resistor element. These are classified as different classes depending upon the energy handling capabilities. Higher class corresponds to higher energy capability. 7.3 Packing, Transport, Handling And Storage Back to contents page (i)

Las are packed vertically on sturdy wooden case. For reasons of fragile porcelain, care should be taken while unpacking, handling and installation so as to avoid impact with hard surface.

(ii)

Immediately on receipt, inspect the cases for signs of transhipment or physical damages packings. In case of any damage matter should be reported to insurance company as well as the manufacturer for guidance.

(iii)

At site the Surge Arrester should e stored in the original packing case and it should also be ensured that boxes are kept in the original vertical condition.

(iv)

While taking out of the cases too, Arrester units should be placed in upright position, the porcelain sheds facing down.

(v)

As LAs are assembled in controlled condition, no attempt should be made at site to open or repair the arrester without consultation of the manufacturer.

(vi)

It is recommended to use nylon ropes for handling the arrester at site.

7.4

Installation Back to contents page i)

LAs are mounted on sturdy structure.

(ii)

Mounting plate of structure top should be regular and horizontal.

(iii)

Check the level with a Spirit Level before mounting.

(iv)

Clean the porcelain surface of insulators.

(v)

Measure resistance preferably by 5 kV meggar. The insulation resistance should be more than 1000 M Ohms.

7.5 Installation of Single Unit Arrester Back to contents page (i)

Fix base plate with 4 bolts (if it was not already fixed) to LA bottom.

(ii)

Base insulators should be placed loosely on the mounting plate of structure.

(iii)

Fix the Surge Counter mounting bracket alongwith one of the base insulator to the structure.

(iv)

Lift the arrester vertically up as shown in figure.

(v)

Lower the Arrester unit and use base insulator stud \ bolt to guide it in place.

(vi)

Fix the Arrester in position.

(vii)

Fix Surge Counter on the Surge Counter Bracket.

(viii)

Connect the stud at the back of Surge Counter to base plate by the connecting link.

(ix)

When surge counter is not in use, base plate should be positively connected to earth.

7.6

Installation of Multi-Stack Arrester Back to contents page (i)

Fix base plate to LA bottom (if not fixed already)

(ii)

Loosen and remove 4 bolts from top of the top units.

(iii)

Fix the corona ring to the top of the top unit / middle unit using the same bolts.

(iv)

Loosen and remove 4 bolts from top of the bottom unit (& Middle unit in case of 3 stack LAs).

(v)

Lift the Top unit and engage 4 studs at the bottom.

(vi)

Lower the top unit to the top of bottom unit (or middle unit in case of 3 stack LAs) by guiding the stud and keeping intermediate plate in between.

(vii)

Fix the units in place. (In case of 3 stack LAs fix the top & middle unit to bottom unit as described above.)

(viii)

Keep the base insulator loosely on the top of structure.

(ix)

Lift the LA (interconnected) and lower the structure top by guiding through the base insulator bolts.

(x)

Fix the Surge Counter mounting bracket with one of the bolts.

(xi)

Surge monitor is connected to the main earth mat in the substation.

(xii)

Ensure that structure is earthed with the earth mat in the substation.

(xiii)

Fix the LA and secure in position by the 4 bolts.

(xiv)

Fix surge counter on the bracket and connect the stud at the back of the surge counter to the base plate.

(xv)

When surge counter is not in use, base plate should be positively connected to earth.

(xvi)

Connection of jumper to the LA, CVT can be made through T clamp or P G clamp or directly connected to the overhead conductor.

DO’S DON’TS & SPECIAL PRECAUTIONS

7.7

Do’s, Don’ts & Special Precautions Back to contents page (i)

Slack span stringing from dead end tower to the gantry should be completed before taking up of the erection of line Arrester.

(ii)

Surge monitors of each phase is to be checked for any damage.

(iii)

The IR value of each stack is to be measured.

(iv)

Use of flexible copper strips between the bushings and earth strips should be preferred.

(v)

Proper care to prevent any damage to the surge bushing should be taken.

(vi)

Insulators should be cleaned before erection at site.

(vii)

Terminal connectors should be tightened to proper torque.

(viii)

Surge monitor has been connected to main earth mat.

CHECK FORMAT

7.8

Check Format Back to contents page

1.

Proper unloading arrangement has been made at site

Yes/No

2.

(Preferably with crane to unload the packages. All items have been checked with the packing list, MICC,

Yes/No

3.

Challans GR etc. After unloading the visual inspection of the packings has been

Yes/No

carried out along with the erection contractor and preferably 4.

with the manufacturer of the equipment. In case of any damage the matter has been reported to the

Yes/No

5.

manufacturer (or insurance agency if required) Slack span stringing from dead end tower to the gantry has

Yes/No

6. 7. 8. 9. 10. 11.

been completed before taking up of the erection of line LA. IR value of each stack has been measured Insulators have been cleaned before erection at site Mounting plate of structure top is regular and horizontall. Level has been checked with a Spirit Level before mounting. Terminal connectors have been tightened to proper torque. When surge counter is not in use, base plate has been

Yes/No Yes/No Yes/No Yes/No Yes/No Yes/No

12.

positively connected to earth. Surge Monitor has been earthed by connecting it to main earth

Yes/No

mat.

___________________________________________________________________ CHAPTER

EIGHT ___________________________________________________________________ ISOLATOR

CHAPTER-8 8.0

Introduction

Back to contents page

ISOLATOR Back to contents page

Isolators are disconnecting switches which are used for disconnecting the circuit under no load conditions. They are installed in such a way that a part of substation circuit can be isolated from other live parts for the purpose of maintenance. Isolators play an important role in maintenance of a substation. An isolator can be opened only after opening the circuit-breaker.

An isolator should be closed before

closing the circuit breaker. Opening and closing of a current carrying circuit is performed by a circuit-breaker. An isolator does not have any specified current breaking capacity or current making capacity. In some cases isolators are used for breaking charging current of transmission lines. 420 kV Centre Break Isolators are designed for independent single pole operation or three pole electrically/mechanically ganged operation. Single or Double Earth Switches, as required, can be fitted to them. These isolators can be operated either manually or by motor. These isolators are supplied in components and are assembled at site. 8.1

Construction features Back to contents page

420 KV Centre Break Isolator comprises of the following: i) Support Structure ii) Base Assembly iii) Insulator Stack iv) Male and Female contacts Assembly v) Operating Mechanism (Main & Earth) vi) Down Operating Pipe (Main & Earth) vii) Tandem Pipe (Main & Earth) viii) Earth Switch Assembly 8.1.1

Support Structure Back to contents page

i) Support Structure are made out of tube. ii) They have the arrangement to fix over the foundation for fixing the Base Assembly on the top of the structure and Operating Mechanism Box (Main & Earth) iii) Earthing strip fixing arrangement is also provided along with. iv) These structures are designed to withstand all forces like short circuit force, wind force and wind load etc. v) Isolator structures are supplied in hot dip galvanised condition 8.1.2

Base Assembly Back to contents page

For every 3 pole switch there are 2 types of bases. i) Base

Assembly

with

drive

arrangement

and

interlocking

arrangement (if the switch is with earth). Other base is without drive arrangement

ii) Stoppers are provided in both ends to control the travel of Moving Blades in both close and open position of isolator. iii) Complete base assembly and other components are duly galvanised iv) Base assemblies are supplied with a) Inter Post coupling pipe assembled and aligned condition b) Inter-Lock arrangement in set condition c) Levers are assembled with pins, friction

washers,

brass

washers and split pins. 8.1.3

Insulator Assembly Back to contents page

Insulators are selected to suit the basic insulation level, minimum creepage and minimum bending load to suit the equipment design requirement. 8.1.4

Male and Female Contacts Assembly Back to contents page

i) In male and female contacts assembly the current carrying parts are made up of Aluminium tubes ii) The male and female contacts (reverse loop design) are made of Electrolytic Copper with Silver Plating. iii) The Connecting Stem is made out of electrolytic copper with Tin Plating/Aluminium. iv) The current transfer part that connects the Aluminium housing and stem is made out of Copper with Tin plating and assembled inside the Housing. 8.2

Operating Mechanism

Back to contents page

Two types of operating mechanisms are available in isolator. 8.2.1

Geared motor operating mechanism Back to contents page

This consists of a reduction gear assembly which is driven by spur gear fitted with 3-phase induction motor through pinion gear, necessary overload protection, control switches for local/remote operation, limit switches and mechanical stoppers. The mechanism can be operated manually in case of failure of supply. 8.2.2

Manual operating mechanism Back to contents page

i) Both the mechanisms are housed in a cabinet made of sheet steel. Auxiliary switches having silver-plated contacts and positive wiping action with adequate number of NO, NC and long wipe contacts are provided. ii) Front door of the mechanism box is provided with good quality neoprene gaskets, which, on compression, when the door is closed, ensures high degree of protection against polluted atmosphere. All the boxes are metal treated before being taken up for painting. Suitable

terminal

blocks

made

of

highly

non-inflammable

thermosetting plastic are provided for terminating control and auxiliary wiring. 8.2.3

Earth Switch Assembly Back to contents page i)

The vertical lift earth employs a turn and thrust

movement by

initially rotating through 90o and subsequently moving upwards by approximately 100 mm.

ii) The earthing switches can be actuated on a individual pole basis or 3 poles can be coupled and actuated by a single drive. iii) Moving Blade of earth switch is made out of aluminium tube and contacts are made out of copper with silver plating. iv) Mounting Base and all other parts are galvanised. 8.3

Receipt , Handling and Storage Back to contents page

i) All packages are to be carefully opened and verified for damages and shortages, if any. These shortcomings have to be properly intimated to the manufacturer as well as to the Insurance authorities as the case may be. ii) Handling of large crates should be handled by crane carefully. iii) All items should be stored on ramps/platforms, free from water logging. iv) All items should be stored in upright position only. v) Insulators are to be stored separately to avoid breakage’s. 8.4

Erection/Installations Back to contents page

8.4.1

Structures Back to contents page

i) Refer the site layout drawings and compare with equipment General Assembly Drawing. ii) Identify the structures according to the General Assembly Drawing iii) Structure assembly is lifted and fixed over the plinth (Without damaging the foundation bolts) iv) Assemble washer, spring washer and nuts in all foundation bolts.

v) Check for level at the top of the structure in both directions by using spirit levels. If required give shims below the base plate of structure and tighten the nuts. vi) All other structures should be assembled in similar way 8.4.2

Base Assembly Back to contents page

i) Identify the Base Assembly from Equipment General Assembly drawing. ii) Lift the base assembly by using proper ropes and place it over the relevant structure iii) After keeping it over the base without removing the rope align it to the mounting hole of base and top plate of structure and fix the bolts and nuts and remove the rope. iv) Check for level of flanges in both direction by using spirit level. v) If necessary add shims below the leg of the base and align it. vi) Tighten all the Bolts. vii) Repeat the installation process for other two poles also. viii)Ensure the Centre line of same pole

and centre line of other

phases are aligned ix) After completing the installation keep all the base assemblies in open position 8.4.3

Insulators Back to contents page

i)

The top middle and bottom units of Insulators should be identified by using Insulator Drawing.

ii)

The bottom and middle units are assembled together by using proper bolts and nuts.

Lift the Insulator stack by using proper

hook and placed over the base assembly by ensuring the top 4 holes position. iii) Without removing the hook align the holes and fix all bolts. iv) The level of top surface of insulator should be checked by spirit level/plumb and if necessary the shims should be inserted below the bottom flange of the insulator or/and between two insulator unit flanges . v)

Now rotate the shaft assembly & check for the rotation of insulator & its eccentricity.

vi) The same procedure is to be repeated for the other side of same pole also vii) In the same way

the top unit of insulator and middle unit are

installed On both sides. 8.4.4

Contacts Assembly (Male and Female Assembly) Back to contents page

i)

Identify the Assembly as per General Assembly Drawing

ii)

Keep the Insulator corona ring on top of the Insulator

iii)

Lift the Male Assembly by using proper sized rope and place it over the insulator above corona ring.

iv)

Without removing the rope align the holes and fix the screws.

v)

Repeat the similar process for female assembly.

vi)

Rotate the bearing shaft assembly and check for alignment of Contacts

assembly for horizontal alignment. Shims should be

inserted between the mounting flange of Assembly and top of

the insulator at relevant side. Similarly for vertical alignment necessary shims should be inserted between insulator flange and top of shaft assembly flange. vii)

If the entry is not smooth, loosen the contacts Mounting screws and push the contacts forward or backward to get free entry.

viii) After achieving the entry check for centre line of Male and Female in both directions. ix)

Now moving part should be rotated 2 to 3 times to ensure the proper alignment

x)

The Corona ring assembly should be identified for male and female unit and connected properly to it.

xi)

Moving part should be operated two to three times for checking the free movement and also check that the contact corona ring are not fouling each other

8.4.5

Connecting Disconnector Back to contents page

i)

Manually set mechanism and disconnector to be connected into fully OPEN position (Arrow mark on top of mechanism cabinet indicates the 'open' and 'close' positions).

ii)

If mechanical interlock keys are fitted, it will be necessary to obtain the relevant keys to make mechanism operational.

iii)

Align the fixing hole and bolt them together to achieve desired tightness.

iv)

Ensure that the mounting channel on the drive and the structure are matching.

v)

Level the box by placing the spirit level on output shaft flange in two directions.

vi)

Provide shim wherever required.

vii)

Check for centre line and verticality between torque bearing flange and drive flange with a plumb.

viii)

Introduce Universal Coupling as called for in the General Arrangement Drawing.

ix)

Measure exact height between torque bearing flange and top of universal flange.

x)

Cut the operating pipe with the specified clearance to facilitate smooth entry.

xi)

Weld

the

vernier

flange

properly

keeping

the

flange

perpendicular to the centreline of the pipe. Level and bolt the same. The drive is now ready for operation. Mounting angles of mechanism to structure are slotted to provide horizontal adjustment. Adjust the mechanism so that the vertical drive tube rotates TRUE. xii)

Cabling (internal/external) be completed as per schematic drawing. Ensure that all electrical interlocks are wired properly.

xiii) Before energising the circuitry, interlock wiring and control wiring should be checked by multimeter (as per schematic drawings) 8.4.6

Controls for Electrical Operating Equipment Back to contents page

A hinged panel on the right hand side of the cabinet carries the electrical controls for operation of the mechanism. Controls for normal

operation are mounted on the front of the panel and are accessible immediately the outer cabinet door is opened These comprise : i)

Local OPEN and CLOSE Control Switch

ii)

In case of individual pole drives the master control cabinet will have push buttons for operating/closing also.

8.5

iii)

Local/Remote Selector Switch

iv)

Heater/Light Switch

Closing Operation of Isolator Back to contents page

i)

Ensure all castle keys are in position.

ii)

Once the associated circuit breaker is open, closing contact

will

energise the interlock thereby making availability of supply at the local/remote selector switch. iii)

Set the electrical remote selector to local position as required and then press push button for closing, thereby causing the closing contactor to pick up.

iv)

The hold on contact of closing contactor will now be closed thereby retaining the supply after the push button is released.

v)

Simultaneously contacts of closing contactor will close, thereby supply to motor is made available.

vi)

Ensure motor direction is towards closing. Otherwise alter the phase sequence at motor terminal box.

vii)

The isolator will start to close, and at the end of the closing operation, limit switch for closing will open then de-energising the closing contactor.

viii) The circuit is now de-energised and the closing operation is completed. ix)

Car should be taken to prevent the mal-functioning. Contact closing (CC) of the closing contactor will isolate the opening circuit, once closing contactor is energised.

8.6

Tandem Pipe Assembly Back to contents page

i)

After single pole trial with motor keep that pole in closed condition

ii)

Fix other two poles also in closed condition (set the stopper screws)

iii)

Measure the distance between the lever of two adjacent poles ('R' & 'Y')

iv)

Check and set the Tandem, pipe length on the floor itself

v)

Lift the Tandem pipe by using proper rope and fix one side first by using suitable anti friction washers, brass washers and split pins.

vi)

Fix other side in the same manner.

vii)

Operate the operating mechanism and check for proper closing and opening of both poles. If required do minor adjustments in Tandem Pipe by length by using adjusting screw. Then finally lock the adjusting screws by check nut.

viii) 8.7

Repeat this process for the other poles ('Y' & 'B')

Earth Switch Assembly Back to contents page

i)

Identify the Assembly to fix the fixed contact assembly through General Arrangement Drawing

ii)

Take the Earth fixed contact assembly and fix it with the Hamper Assembly by using proper sized Bolts as per General Assembly Drawings. The above assembly can be carried out before installing the Hamper Assembly over the insulator.

iii)

Lift the Earth Blade Assembly by using rope and fix it with base assembly using the middle set of mounting holes to hold the assembly in place.

iv)

Attach counter balance weights in pendulum arm at suitable hole and check the position of Earth Switch which should be parallel to ground.

v)

Manually move earthing blade towards closing position .To adjust add shims at the back of the mounting plate to tilt the earthing blade in required direction.

vi)

Continue to move earthing blade towards closing and observe that the contact

fingers come into the fixed contact. A small

adjustment to twist the contact fingers is possible by shimming mounting plate. vii)

Continue to close earthing switch until contacts are fully engaged i.e. when the insulated stop of the earthing blade comes to rest without straining against fixed contact.

viii) Tighten all fixing bolts and keep the earth switch in closed position.

DO’S DON’TS & SPECIAL PRECAUTIONS

8.8

Do’s, Don’ts and Special Precautions Back to contents page

i) Before the isolator is put into operation, the motor is to be meggered and the contacts are cleaned. ii) The mechanism box

always is to be kept free from moisture.

Hence, space heaters are provided in the mechanism box. iii) Also rubber beading should be kept in good condition. iv) Cable glands should be properly fitted at the entry of the cables and extra holes are plugged properly to avoid hazards. v) For transportation, individual base and bearing pole assemblies & the male and female contact arms should be packed separately. The Insulators and drive boxes should also be packed separately. vi) The bolts and nuts required for mounting the base to the structure and the Insulators to the base are packed separately as loose items, while all the other hardware (bolts & nuts) are fitted in their respective places. Care should be taken that these are removed only at the time of mounting to respective assemblies. vii) All the assembles should be stored well preferably in a covered area to avoid any damage/pilferage during storage.

8.8.1

Adjustment in drive/assembly erection Back to contents page

i)

Manual

a)

By use of emergency handle, operate the coupled disconnector and observe whether it is fully OPEN or CLOSE at each end of its operating cycle

b)

If isolator does not CLOSE fully remove clamping bolts and turn mechanism slightly towards /OPEN and retighten bolts proceed turning isolator towards CLOSED.

c)

Repeat until satisfactory operation is obtained.

ii)

Electrical

a) Make electrical connections by referring to contract diagram of connections of incoming supply. b) Do not attempt to operate the disconnector under power at this stage. c) When selector switch is fitted set it to LOCAL d) When AC Motor is fitted manually set mechanism to mid position. e) Operate control Switch and at the same time observe whether the mechanism rotates towards the selected position f) If it rotates in opposite direction to that selected stop motor immediately by switching off power supply. g) If necessary reverse the to phases of motor supply. iii)

Open and Close Push Buttons The Control Push Buttons determine the direction of travel of the isolator. When a cycle is initiated by switching to the appropriate position the isolator will open or close. Once the mechanism has received a signal the push button can be

released. The

mechanism will complete the operation and will not respond to further signals until it has completed its operation. An indicator, shows the isolator position either OPEN or CLOSE outside the cabinet at the base of the output shaft. iv)

Selector Switch

When the selector switch is set to LOCAL, operation of the mechanism will be governed by the controls in the cabinet. Setting the selector switch to REMOTE transfers controls of the mechanism to remote control point. v)

Heater and Heater Switch An anti-condensation heater is fitted in the bottom of the cabinet. It should be switched on at all times, ensuring that the temperature inside the cabinet exceeds the temperature outside. The heated air leaves the cabinet by way of breather around the output shaft and cool air is sucked in. A switch is mounted on the front of the control panel for the control of the heater through a thermostat.

vi)

Open and Close Contactors These contactors are mounted side by side on the rear of the electrical control panel. They directly control the reversing operation of the motor. Further contacts are used for electrically interlocking the contactors, providing a sealing circuit across the 'OPEN' and 'CLOSE' Push Buttons.

vii)

Auxiliary Switches Silver plated contacts with a positive wiping action are used giving reliable making of low current signalling circuits under adverse climatic conditions.

viii)

Fuse Links Fuses for the control and heater circuits are mounted on the control panel. Connections to these are made in the same manner as connections to terminal blocks. The fuse wire is

routed through the top of the carrier. The current ratings of fuselinks are shown on the schematic diagram drawing. For opening the Isolator a similar sequence of operation will be executed by pressing the push button for opening.

ix)

Manual Operation The mechanism may be operated manually in the event of a motor power failure with the help of manual operating handle.

CHECK FORMAT

8.9

Check Format Back to contents page

1.

Proper unloading arrangement has been made at site Yes/No (Preferably with crane) to unload the packages.

2.

All items have been checked with the packing list, MICC, Yes/No Challans GR etc.

3.

After unloading the visual inspection of the packings has been Yes/No carried out along with the erection contractor and preferably with the manufacturer of the equipment.

4.

Any type of damage to the equipments/components during Yes/No transportation or any missing items has been brought to the notice of the panel supplier.

5.

Site where isolator is to be erected is ready before the starting

Yes/No

of erection work. 6.

Level of the structure assembly has been checked during

Yes/No

erection using spirit level 7.

Site where isolator is to be erected is ready before the starting

Yes/No

of erection work. 8.

Level of the top surface of isolators has been checked during

Yes/No

erection, alignment & level of equipment 9.

Centre line of all the poles in different phases are aligned.

Yes/No

10.

Centre line alignment of male & female assembly has been

Yes/No

checked 11.

Before fitting, the crane rings have been identified for male and

Yes/No

female assembly 12.

Moving parts have been operated 2-3 times for checking the

Yes/No

free movement 13.

The rotation of motor is in right direction

Yes/No

14.

In case it is in opposite direction the same has been corrected

Yes/No

by altering of the phase sequence of the motor terminal.

15.

Lifting of tandem pipe assembly is with proper size rope

Yes/No

16.

During erection movement of earthing blade has been checked

Yes/No

17.

Contact fingers of earthing blade and moving towards the fixed

Yes/No

contact 18.

All fixing bolts have been tightened to keep the earth switch in proper close/open position

Yes/No

CHAPTER-9 CURRENT TRANSFORMER

___________________________________________________________________________ CHAPTER

NINE ___________________________________________________________________________ CURRENT TRANSFORMER Back to contents page

9.0

Introduction Back to contents page

Current transformers are used for reducing/stepping down ac current from higher value to lower value for measuring /protection /control. CTs have low VA rating. Rated characteristics of CTs used for High Voltage metering/ protection are given below: i)

Rated primary current

ii) Rated short time current (primary) iii) Rated secondary current iv) Rating exciting current v) Rated burden vi) Current error or ratio error vii) Phase angle error viii)Composite error ix) Accuracy class i)Over current factor ii)Insulation level (primary) 9.1

Construction Features Back to contents page

Construction-wise the Current Transformer may be of following two types: Hair Pin design or dead tank type and Top dome design or Dead Tank design. In the hairpin design the primary conductor enters from the top of insulators and passed through the tank.

The secondary core is

wound on the primary inside the tank. The body of tank is earthed to the switchyard earthing. Current Transformers of WSI, BHEL, ABB are of this type. In the other top dome design the Primary conductor goes straight in the dome shaped tank at the top. Secondary winding is wound against it. As the tank body is always live this design is known as the live tank design. Current Transformers of CGL, RK are of this design. As the head is heavy, more care is required while lifting and alignment of the CT. The Current Transformer essentially consists of primary and secondary coils and core. The core is constructed in the form of rings. The secondary winding is wound uniformly over the insulated ring cores. The secondary terminals are brought out through a terminal board into the terminal box. From terminal board the connections are given to the terminal blocks. The control cables are

connected to the terminal

blocks. The primary winding consists of Copper strips/Aluminium pipe (with single turn) over which high quality insulation paper is wound. Aluminium foil is wrapped at suitable intervals over the insulation paper to get a constant voltage gradient along the arcing distance of the porcelain insulator.

The insulated primary passes through the

porcelain insulator and taken out through 4 nos. terminal bushings

(each rated for 1200 A) fixed to the wall of the expansion chamber. The respective terminal bushings are shorted internally. The primary conductor has sufficient cross sectional area to meet the continuous and specified short-time current ratings. The outer surfaces of ferrous parts are given light grey enamel paint to shade over rust inhibitive coat of ready mixed zinc chrome primer. Steel surfaces coming in contact with transformer oil are given a coat of oil resisting varnish. Galvanised bolts and nuts are used as fasteners. All welded and gasket joints are subjected to leak tests. 9.1

Hermetic Sealing Back to contents page

The current transformer is subjected to heat and vacuum cycle in a drying chamber to extract the moisture from the insulation paper. After drying and oil impregnation under vacuum, the current transformer is hermetically sealed with dry Nitrogen gas above oil.

When the oil

expands or contracts due to temperature variations, the Nitrogen gas in the chamber undergoes change in pressure.

Depending on the

pressure and temperature, a part of Nitrogen gas in the chamber undergoes change in pressure and a part of Nitrogen gas will be absorbed by oil.

The volume of expansion chamber and the gas

pressure at the time of initial filling are adjusted so that the gas pressure will be less than + 0.5g/cm2 at 75oC and above -0.2 kg/cm2 at 0oC. A drain valve is provided at the bottom of lower tank. Some CTs come with rubber/teflon/steel bellows to take care of temperature variations. Such CTs are not filled with Nitrogen gas. 9.2

Transportation, Unpacking & Inspection

Back to contents page

i)

The 400 kV current transformer is dispatched in the horizontal position (with the oil level gauge side at the top) fixed to a transportation frame in wooden crates whereas 220 kV CT is positioned vertically in packing.

ii)

Special oil sealing arrangement is provided in the expansion chamber to prevent contact of Nitrogen gas with paper insulation when the current transformer is in the horizontal position.

iii)

For unloading /loading the crates, crane should be used in store and switchyard. However, truck should be used for transporting the CT from store to switchyard.

iv)

CT at site should always be lifted from lifting brackets which are provided on the base.

v)

Unpacking of wooden crates should be done with particular care so as not to damage the porcelain insulator and terminal bushings.

vi)

After receiving at site CT should be checked for any physical defect.

vii)

The name plate readings/rating of CT should confirm to technical specification of our LOA.

viii)

All the crates containing different parts of CT should be checked with the store challans/MICC/Packing list etc.

ix)

CT should be lifted by crane using chains/strings from the indicated handling points on crates.

x)

400 kV CT is to be made vertical immediately on receipt at site and kept in vertical position only.

9.4

Installation/Erection Back to contents page

i) As the current transformer is dispatched in completely assembled state, it can be installed directly after making it upright. It is to be ensured that before commissioning, the porcelain insulator is clean and free from all dust, grease and particles of packing material. ii) Alignment of the support structure should be checked with spirit/water level. iii) Place the CT on duly levelled supporting structure by using a crane.

iv)

Care should be taken such that primary polarity of erected CT is correct and as per relevant drawing.

v)

Fix the CT with four anchor bolts to the supporting structure.

vi)

Now the crane can be removed after tightening the bolts & nuts.

vii)

Provide proper earthing of transformer from the base of CT. Earthing connection should be permanent.

viii)

Lay the control cables from control room relay panels and connect to CT marshalling box.

ix)

Control cables should be laid in trays or in pipes.

x)

Marshalling box of CT should also be earthed.

xi)

Cabling work on secondary side should also be completed & its IR valve be ascertained.

xii)

Cable continuity should be checked after erection is completed.

xiii)

Star point should be earthed properly.

xiv)

Care should be taken during handling, lifting, loading or unloading and erection no damage is done to CT insulator by slings. Proper cushioning arrangement should be used for the same.

xv)

The receipt storage and erection should be done as per the approved FQP.

xvi) The threaded fasteners should be clean & tight and missing or broken fasteners should be replaced. xvii) It should be ensured that all the times the oil in CT is at the specified level and there is no leakage of oil.

xviii) The primary injection test of CT should be carried out as per the prescribed procedure. xix) Any secondary core of CT that is not being put in service should be short circuited. xx)

Polarity of all secondary cores should be checked.

DO’S DON’TS & SPECIAL PRECAUTIONS

9.5

Do’s Don’ts & Special Precautions Back to contents page

i) In order to keep the unit hermetically sealed, the flanged joints with gaskets in between should not be tampered with. The cover of the secondary terminal box alone needs be opened for giving connections to control cables. ii) Since the current transformer is hermetically sealed and uses no material harmful to oil, there is no necessity for extraction of samples of oil for analysis or for reconditioning of oil. Check for Nitrogen gas pressure is also not required. If oil level is below the red mark it indicates leak and should be investigated. iii) In case of heavy pollution deposits due to surrounding atmospheric conditions, periodic external cleaning of porcelain insulator and cleaning/painting of other exposed surfaces can be carried out (as per the specific instruction of the manufacturer) iv) Precautions should be taken not to keep open secondary circuit when current is flowing in the primary as this may cause overheating of core and breakdown of the insulation due to high voltage developed across the secondary terminals. v) The lower tank should be earthed in a positive and permanent manner before commissioning. vi) The CTs are dispatched with secondary terminals short circuited. Care should be taken so that the shot circuiting links at the terminals are not disturbed.

vii) For lifting the CTs at site one should look for proper handling points for using slings and read the specific manufacturer’s instruction to avoid any mishap. viii)Weight

of

the CT

plates/specifications &

should be

read from the name

lifting tackles of ample capacity should be

used. ix) Crates of CT should be lifted without jerks or vibrations and placed at the desired place without dropping or hard hitting on ground.

CHECK FORMAT

9.6

Check Format Back to contents page

1.

Proper unloading arrangement has been made at site Yes/No (Preferably with crane) to unload the packages.

2.

All items have been checked with the packing list, MICC, Yes/No Challans, GR etc.

3.

After unloading the visual inspection of the packings has been Yes/No carried out along with the erection contractor and preferably with the manufacturer of the panels.

4.

Any type of damage to the packing during transportation or Yes/No any missing items has been brought to the notice of the manufacturer.

5.

The unpacking of CT has been done carefully to avoid any Yes/No damage to it.

6.

Site where CT is to be erected is ready before the starting of

Yes/No

erection work. 7.

It has been checked that there is no leakage of oil from CT

Yes/No

8.

Cranes or other good quality lifting T&P is available at site to Yes/No transport/ CT from store to site and for erection

9.

Care has been taken to avoid any damage to insulators Yes/No during lifting (by providing cushion of suitable material)

10.

Oil level in CT has been checked

Yes/No

11.

IR value of primary and secondary winding recorded & Yes/No satisfactory results are obtained

12.

CT has been placed on the support structure very carefully Yes/No and all nuts have been tightened.

13.

The structure/equipment has been levelled

Yes/No

14.

The polarity of CT is correct

Yes/No

15.

The table of CT has been earthed at two points

Yes/No

16.

The marshalling has been checked for heating and lighting Yes/No arrangement

17.

The cable work between C&R panel to marshalling box is Yes/No complete.

18.

Continuity of all cables has been ascertained

Yes/No

19.

Primary injection test of CT at relay terminal has been Yes/No performed as per prescribed procedure.

20.

Secondary core of CT that is not in use has been short Yes/No circuited.

CHAPTER-10 CAPACITIVE VOLTAGE TRANSFORMER

___________________________________________________________________________ CHAPTER

TEN ___________________________________________________________________________ CAPACITIVE VOLTAGE TRANSFORMER Back to contents page

10.0

Introduction Back to contents page

Capacitive

voltage

transformer

can be effectively employed as a

potential source for metering, protection, carrier communication and other vital functions of an electrical network. In the case of EHV systems CVTs are always supplied in multi-unit construction. The multi-unit construction enables ease of transportation and storage, convenience in handling and erection etc. 10.1

Description & operating principle: Back to contents page

The Capacitive Voltage Transformer comprises of a Capacitor Divider along with its associated Electro-Magnetic Unit. The Divider provides an accurate proportioned voltage, while the Electro-Magnetic Unit transforms this voltage, both in magnitude and phase to convenient levels suitable for metering and protection. The

Electro-Magnetic

Unit

components; 

Compensating Reactor



Intermediate transformer



Damping device

(EMU)

comprises

of

the

following

The compensating reactor is used for tuning CVTs to the desired rate frequency of 50 Hz. Since the CVT comprises of capacitors the compensating reactor plays the role of nullifying the capacitive effect of reactance due to the capacitance of the CVT. The capacitor unit comprises of HV capacitor C1 & intermediate voltage capacitor (C2).

These capacitor consist of oil impregnated,

series connected capacitor elements; housed inside oil filled porcelain insulators. Each capacitor unit is hermetically sealed. i)

Capacitor Units

It comprises of metallic bellows to compensate for volumetric expansion of oil inside the Porcelain. In case of multi-unit stack all the potential points are electrically connected and shields are provided to overcome the effect of corona and RIV. ii)

Transformer

The voltage tapped from the intermediate point of the capacitor is fed to the primary of the transformer through the choke. This tapped voltage is stepped down by the intermediate voltage transformer to the required rated secondary voltage. Typical Transformer Ratings In case of 400 kV/4000/6600 pf and 400 kV/8800 pf CVT the rating of transformer may be

Table -1: Rating of Transformer 1.

Rated primary voltage

22/3 or 20/3 kV rms (Primary of intermediate voltage transformer)

2.

Rated secondary voltage

110/3

V

(across

each

secondary

winding) 3.

Total simultaneous burden

4.

Rated output burden and accuracy Winding 1 : 200 VA 3P class per winding

300 VA for 0.5 class accuracy

Winding 2 : 200 VA 3P Winding 3 : 100 VA 0.5

The transformer is made up of CRGO laminations of core type design over which primary and secondary windings are wound around the laminations. The insulation between the core and the windings and interturn insulation is done by means of paper. iii)

Details of capacitor divider unit :

The Capacitor divider unit is used acts as a i)

Coupling capacitor for carrier communication.

ii)

Voltage divider for stepping down the voltage to a suitable level. This stepped down voltage is fed to the primary of the transformer through a choke (compensating reactor) which is housed inside the electromagnetic unit. The Capacitive

Divider normally comprises of capacitor

elements of cellulose paper dielectric with aluminium foil electrode. These elements are identical and are connected in series by using copper taps. Hence the voltage across each element is identical. The reduction in voltage is achieved by taking tap from one of the capacitor elements. 10.1

Packing and Transportation : Back to contents page

i) All Capacitor Units or the Capacitive Voltage Transformer are securely

packed in wooden crates.

The Electro-Magnetic Unit

forms an integral part with the capacitor unit. In the case of MultiUnit type, the bottom most capacitor unit is hermetically associated with the Electro-Magnetic Unit. Each wooden crate is identified with the corresponding serial number of the unit inside. ii) Each Capacitor unit has one Name Plate designating the rating of the unit.

Position of the Unit in the complete assembly is also

indicated in the Unit Name Plate by incorporating Top Unit or Middle Unit or Bottom Unit. iii) Bottom-most unit of Multi-Unit stack has one Master Name Plate fixed on to the Electro-Magnetic Unit and one unit Name plate fixed on to the bottom flange. iv) The transportation must be performed in vertical position only. Transportation should be carried out as smoothly as possible without undue jerks. v) The unpacked parts of the device should also be moved in the same vertical position as within the packing 10.3

Receiving Back to contents page

While receiving the CVT the site should check : i) That the right CVT has reached at the destination with regard to its voltage and other rating particulars. ii) Ensure that CVTs are not mislinked.

iii) Look for transit damage before proceeding with any unloading operation. Where a doubt arises, apprise the insurance authority or insist on open delivery from the Transport Carriers. iv) Inspect for breakage’s. In case of the manufacturer should be notified immediately. v) During handling, ensure that the capacitor Unit is always its upright vertical state. 10.4

Unloading : Back to contents page

Before unloading the crate(s) of the CVT from the carrier or transporting vehicle i) Carefully observe the instructions on the wooden crates. ii) It is important to look for sling or chain markings, supporting points etc. and use them. iii) Ensure that the Top and Bottom ends of the crates are in order. iv) Make arrangements for unloading with derricks or cranes and with associated hoisting facilities. v) Unload the crates one by one, taking all precautions required for fragile material. vi) As all porcelains are fragile and are susceptible to breakage, avoid knocks and jerks during handling. vii) The base unit should be lifted with crane by means of lifting lugs provided on the EMU cover. Otherwise there is danger of breaking a porcelain bushing. viii)For taking the capacitor unit out of packing, use lifting lugs provided on top cover of capacitor.

ix) While unloading/unpacking, vibrations, shocks are to be avoided. x) The separate capacitor unit must be short circuited by bare wire between head & bottom flange until erection and connection are completed. 10.5

Storage Back to contents page

i)

CVTs are dispatched with the terminals short circuited. Store the Capacitor Voltage Transformers taking care that the short circuiting at the terminals is not disturbed.

(ii)

A free capacitive voltage transformer with its terminals not short circuited picks up dangerous potentials which may cause injuries to personnel.

iii) It is also to be ensured that the CVT should be kept always in vertical position. iv) When not in use keep the Capacitive Voltage Transformers away from energised locations, water logged areas, marshy or humid locations. v) When CVT is to be stored, it should be put back into trapezoidal crate/packing case. If prior to the installation, the CVT is to be stored for longer duration without usage, the following

tests may be carried out

on the CVT.

10.6

a)

Visual inspection as per approved drawing

b)

Measurement of capacitance

Installation Back to contents page

i)

Before proceeding with the installation, keep all the units near the erection site.

ii)

Ensure that the Top, Middle and Bottom units are (if applicable) properly identified as per their serial numbers indicated on the name plates.

iii)

Base unit is to be fixed on a supporting structure with bolts of specified size.

iv)

For fixing the base unit, 4 holes are provided on the bottom plate of the EMU unit.

v)

If, there is an upper capacitor unit then it is to be fixed with the top flange of the lower unit with the help of studs, nuts and washers

vi)

For assembly of capacitor units which have antifog shads on the porcelain or which have broaden sheds, the threaded studs used for coupling have to be first held into the through holes of the flanges, before the units are placed are above the other. The assembly has to be done with utmost care, to prevent damage to the porcelain sheds.

vii)

For handling the base unit & upper capacitor during the erection process, use of crane is necessary.

viii)

The studs used for coupling the capacitor units have to be tightened with the specified torque.

10.7

Connection Back to contents page

i)

The upper terminal of individual capacitor unit should be short circuited to the base by basewire till all connections are

completed and unit is ready for commissioning care should be taken to remove this bare wire prior to commissioning. ii)

The tank of CVT base of CC should be earthed properly at two independent places

iii) In case of CVT if carrier frequency terminal is not to be used it should be earthed on the steel tank. iv) The line matching unit is to be connected between HF bushing outdoor and earth if CVT is used for carrier coupling otherwise this terminal is to be earthed. v) Connection work in the secondary terminal box should be done when HV terminal is earthed. vi) The cables with large cross sections are inserted through the bottom of the terminal box. The connections should correspond to the circuit diagram on the inner side of terminal box. vii) The earthing of secondary winding (s) must be done either in the terminal box at the beginning or at the end of cable but not at the both ends. It is preferable to earth the secondary terminal in terminal box. viii)However for open-delta connection protection scheme for earthing of secondary winding should be referred. ix) The quick acting fuses for each secondary windings are mounted in the terminal box itself. x) The secondary terminals must not be touched and the head of the person attending this job should be below the level of the tank cover.

xi) Only metering winding for monitoring equipment and protecting winding for protective equipment should be selected. xii) Unused secondary windings should be left open circuited and in no case they should be shorted. xiii)The tank should be earthed by means of copper conductor, the cross section of which complies with the statutory regulations. One end of the secondary winding should also be earthed. xiv)After confirming the low voltage ratio, connect the HV terminal to the line by terminal connector.

While clamping the terminal

connector proper torque should be applied to ensure firm connection.

xv) It should be ensured that the jumper is rightly connected to the primary terminal of CVT. xvi)Pre -Commissioning checks should be carried out as per the norms of Corporate Operation Services Department.

DO’S DON’TS & SPECIAL PRECAUTIONS

10.8

Do’s, Don’ts and Special Precautions Back to contents page

i) In case of multiunit construction the capacitance of each divider is to be measured separately. In case of bottom divider the same has to be removed along with the bottom flange from the EMU tank. ii) After removing the bottom divider from the EMU check for any loose connection of EMU. This test may be carried out using the shearing bridge. iii) Measure the depth of the bellow. iv) In case of any evidence of traces of oil do not energise the CVT. v) Measurement of voltage ratio vi) Apply a very low voltage say 230 V and measure the secondary voltage across each winding.

It should be matching the

specifications of the manufacturer. vii) Carry out the meggering test on LV terminal of EMU by using 500 V megger. viii)The measured value should not be below 10 M ohms. ix) Check the resistance of the damping resistors after disconnecting the connecting leads from the secondary terminal studs. x) The CVT should always remain in its upright position to safeguard mechanical arrangement of the internal active parts. 10.8.1

Inspection before mounting Back to contents page i)

Oil level in the tank is to be checked. The red line on the oil level gauge indicates rated oil level at 20o C.

ii) Tightness of the tank and capacitor units is to be checked. All units (oil level gauge, cover, oil drainage joints) should be checked for oil levels. iii) A leakage at the insulator indicates defect in transportation. In case any leakage is detected, the unit should not be installed and manufacturer to be contacted. iv) Before the CVT is placed in position, check with a 500 V DC Megger whether the internal connection to the primary and secondary windings are intact and property connected. v) CVT secondary winding should never be short circuited. vi) While connecting the measuring instruments, protective relays to the secondary terminal, ensure the load/burden on respective secondary winding is not exceeded. 10.8.2

Defect/Damage Back to contents page

i) If defect/damage is noticed, matter should be reported without any delay to the manufacturer with full details like type, designation and serial number of equipment, nature of defect/damage and exact location of defect . ii) When the device i.e CVT/CC consists of two or more than two units it must be insisted

that each upper unit is mounted up on

corresponding base unit. iii) The units are calibrated at manufacturer’s works before they are despatched.

Therefore pay attention to date (manufacturing no,

from the last certificate) on the rating plate and on special plate at

top cover of the upper units. Upper units pertaining to different CVT should not be assembled together. iv) Corona shield in two halves are supplied loose in the same packing case and it is to be fixed after mounting top units. In case of multi unit CVT the unit with single capacitor stack is generally supplied with Corona shields duly mounted. v) Small repairs (defects on surfaces) may be done at site. Leakage should be reported to the manufacturer with a statement of Item No., Order No., date of commissioning and other specifications. 10.8.3

Minor Irregularities Back to contents page

i) Should the insulator gaskets begin to leak slightly for instance, tighten up the clamp holding the insulator in an attempt to stop the leakage. The nuts should be tightened up successively by about 1/6 of a turn until they are all uniformly tight the maximum torque being 70 kg-cm. ii) Careless excessive or uneven tightening of the nuts may damage the insulator If tightening up does not stop the leakage the matter should be reported to the manufacturer. iii) If a secondary bushing, is leaking try to stop the leakage by tightening the nuts slightly. If the leakage does not stop, matter should be reported to manufacturer. 10.8.4

Erection Back to contents page

During installation the studs used for coupling capacitor should be tightened by applying torque of specified strength.

i) During erection process of CVT at site preferably the crane should be used for handling the different units. iii)

It is to be ensured that capacitor unit with same serial numbers are coupled during erection of CVT with 2 or more capacitor units.

iv)

Upper as well as the lower capacitor unit has to be short circuited & connected to earth, until the erection and commissioning work is being done on the CVT. (The capacitor get charged by the electrical fields in the vicinity and they keep these changes for a long time, which can be dangerous to human life. Hence the shorting of capacitor unit is necessary).

v)

No screwed joint of the capacitor units and base units should be unscrewed.

CHECK FORMAT

10.9

Check Format Back to contents page

1.

Different CVT units have been transported and stored in Yes/No vertical position

2.

Physical verification of CVT done as per specifications, Yes/No challans, BOQ, MICC etc.

3.

Unloading of CVT done using crane

Yes/No

4.

CVT checked for any physical damage, discrepancy etc.

Yes/No

5.

Oil level in CVT is OK

Yes/No

6.

In case of any damage/discrepancy same has been reported to Yes/No supplier/insurance agency.

7.

Proper lifting arrangement for different CVT items at site being Yes/No provided

8.

Mounting bolts of base plate have been tightened properly

Yes/No

9.

Various parts of CVT joined and tightened to the designed Yes/No torque

10.

HF terminal of unutilised CVT is properly earthed

Yes/No

11.

Care has been taken to avoid short circuiting of CVT Yes/No secondary winding

12.

Crane is used for handling the capacitor units

Different 13. erection activities performed as per approved FQP.

Yes/No Yes/No

14.

Fuses in CVT marshalling box are OK

Yes/No

15.

Cable laying activity is complete from relays to marshalling box

Yes/No

16.

Proper earthing of CVT tank has been done

Yes/No

17.

Terminals have been properly tightened.

Yes/No

CHAPTER-11 POWER LINE CARRIER COMMUNICATION

___________________________________________________________________________ CHAPTER

ELEVEN ___________________________________________________________________________ POWER LINE CARRIER COMMUNICATION Back to contents page

11.0

Introduction Back to contents page

In the modern Power System network for stable operation of large network a reliable communication is required. Difficulties in obtaining reliable and cost effective communication medium limit the choice of the Communication medium to power line carrier (PLC). The same power lines

carrying the Electrical

Energy

are utilised for

Communication. 11.1

PLC System Back to contents page

PLC system are principally used to carry information in the form of speech or the form of data representing Telemetering, Telecontrol, Teleindicator and Teleprotection. The signals are transmitted by means of H.F. carrier Trans/Receiver, the carrier frequency may be anywhere between 30 kHZ and 500 kHZ the information wave band is 300 HZ to 3.4 kHZ.

11.2

Speech Band

=

300 HZ to 2 kHZ

Data Band

=

2 kHZ to 3.4 Khz

Coupling Equipment Back to contents page

To enable the Power Lines to be employed for Communication purposes some from of coupling equipment is required which will permit the injection of Higher frequency carrier signals without undue loss and at the same time de- couple the Communication equipment from the power unit. 11.3

Coupling Equipment Description Back to contents page

Essentially Coupling Equipment Comprises of the following i)

Capacitive Voltage Transformer (CVT) Coupling capacitor (8800 pF to 22000 pF) of suitable voltage withstanding

capability

is

inserted

between

the

carrier

equipment and HV Line which isolates the H.F. equipment connected on LV side from HV side. The coupling capacitor passes the H.F. frequency signals and blocks the power frequency signals towards carrier section. ii)

Wave Trap/Line Trap The coil is rated to carry full line power frequency current; the rating of choke is 0.1 to 1.0 mili Henry. Tuning pot in parallel with coil is used as tuning device to block the carrier frequency entering the substation. Line trap unit is inserted between busbar and connection of coupling capacitor to the line. It is parallel tuned circuit comprising L and C. It has a low impedance (less than 0.1 ohm) to 50 Hz and high impedance to carrier frequencies. This unit prevents the flow of carrier signal towards substation and at the same time offers negligible impedance to the power frequency current.

The line traps are connected in series with the high voltage lines on the station side. These are designed for the following ratings: 

Normal power frequency current



Short-time short-circuit current



Basic insulation level characterised by the normal power frequency voltage, lightning impulse withstand voltage and switching impulse withstand voltage.

11.4

Constructional Features Back to contents page

The line trap unit comprises of the following main parts: 

Main coil



Tuning Unit



Lightning Arrester.



Corona ring for 400 kV Line Trap (this is generally supplied loose, it should be fitted before lifting for erection)

11.5

Data Transmission Back to contents page

The important analogue and digital parameters of the substation are transmitted to the load despatch centres for SCADA and EMS functions. 11.6

Teleprotection Back to contents page

For high speed protection particularly at 400 kV system the fault should be isolated within 100 ms time. Use of carrier signals help in reducing the fault isolation time. 11.7

Carrier Panel

Back to contents page

In the transmitter section, the AF signal is converted into H.F. signal in two stages, i.e. first AF is converted into IF (Intermediate frequency ) and

then converted

into

H.F. (higher frequency). Apart from the

signals i.e. (speech, data and Teleoperation) the other signals which are internally generated i.e. pilot and auxiliary are also converted into H.F. stage. The pilot is normally used for calling opposite station either through dialling or through express. It also does the main function of guarding the receiver against generating AGC voltage (automatic gain control). The purpose of Aux. Carrier is to see that transmitter and receiver work in frequency locked mode. 11.8

Earthing Back to contents page

The last but not the least important is earthing of the PLC terminals and panels. The earthing should be proper and common with Substation earthing to safeguard the Electronic Component and working personnel from any voltage gradient. Earthing at different points may lead to excessive currents between outdoor and indoor PLCC equipment. These excessive current can damage the output stage of the carrier terminal. 11.9

Erection of PLCC and associated equipment Back to contents page

The installation should be done as per planned system. The equipment allocated for a particular section/ station should not be diverted. This may result in complications at a later stage because of crowded carrier spectrum.

The Power Line Carrier Communication Equipments are basically divided into two groups; viz:-

11.9.1

i)

Outdoor equipments and

ii)

Indoor equipments

Outdoor equipments Back to contents page

i) a)

Line Trap Suspension Mounted The main Line Trip coil and the Tuning Pot/Lightning Arrester are supplied separately. Generally before raising the Line Trap for hanging from the gantry the Tuning Pot and Lightning Arrester must be installed and connected. The Line Trap should be hung from the gantry with the help of the insulating string and ball and socket joint. The necessary clamps for hanging the Line Trap from the gantry are as under:

Ball and Socket arrangement for connecting the insulator string to the central rod of the Line Trap;



Flat pad Aluminium clamp for connection of the Line Trap incoming terminal to ACSR Jumper;



Flat pad Aluminium clamp for connecting Line Trap outgoing terminal to station equipment.

The Line Trap is suitable for outdoor pedestal or suspension mounting and should be mechanically strong enough to withstand the stresses due to maximum specified wind pressure. b)

Pedestal Mounted

For pedestal mounting, each line trap shall be mounted on a tripod structure formed by three insulator stacks arranged in a triangular form.

All the accessories and hardware, mounting

stool including bolts for fixing the line trap on insulators are of non-magnetic material. Terminal connectors may be welded with the Traps or it may be supplied separately also depending upon the manufacturer. The conductor take off (Horizontal or Vertical) from the Line Trap should be ensured as indicated in the Line Trap drawings if the Line Trap is to be connected with 4” IPS pipe . Generally it is not possible to connect the pipe directly on the Line Trap. ii)

Coupling Device The coupling device is interposed between the capacitor voltage transformer and coaxial line to the PLC transmitter/receiver, and in conjunction with the capacitor voltage transformer to ensure: 

Efficient transmission of carrier frequency signals between the carrier frequency connection and the power line.



Safety of personnel and protection of the low voltage parts and installation, against the effects of power frequency voltage and transient over voltages.

For direct and efficient earthing of its primary terminals, the coupling device is equipped with an earthing switch. The Earth Switch is available for earthing of CVT-HT terminals, when the coupling

filter

units

maintenance/replacement.

are

removed

from

circuit

for

The coupling device is suitable for outdoor mounting. All the elements of coupling device are fitted on a base plate having pad locking arrangements. The HT Terminals of coupling device is connected to H.F. Terminal of the CVT by means of copper wire of specified size with suitable lugs & taped. The impedance points available on coupling device should be checked with respect to available H.F. cable impedance. The H.F. point of CVT on which coupling device is not mounted must be earthed. Other two CVTs are earthed through coupling device. iii)

Earth Switch

The Coupling Device is earthed through this earth switch during maintenance. 11.9.2

Indoor equipments Back to contents page

i)

Telephone Equipment The telephone equipment is either housed in the same steel cabinet which is used for housing the carrier set or in a separate steel cabinet. If the equipment is housed in a separate steel cabinet, the cabinet should be mounted on concrete plinth or steel structure will depend upon the dimensions of the cubicle housing telephone equipment.

ii)

Interconnection Cables Various

types of Interconnection Cables are required for

connecting the Indoor Equipment.

The Cables which are

required for power Line Carrier Communication Equipment are indicated hereunder for general guidance:a)

Power Supply Cables

Standard 3 core PVC cable is used for connection between the power supply point and the Float Charger. The cable length can be decided depending upon the position of the Float Charger. Interconnection

between

Float

Charger

&

Battery/Carrier

Equipment and Telephone Equipment requires 48V DC supply 3 Core PVC cable. The cross section of the cable to be used will depend upon the current rating and the distance of the equipment from Battery/Float Charger. The length of the cable will depend upon the layout of the Substation and the position of the Carrier Room, Distribution Board, Battery Room etc. The PLCC equipment is operated, on 48 V DC supply. Normally battery charger feeds the load and trickle charges the Battery. In the event of AC failure the battery feeds the load. Further looping of power supply may be done at PLCC panels ends. b)

Co-axial Cable The outdoor Co-axial Cable is used for connecting the Line Matching Units/Line Matching & Distribution Units/Coupling Filters/Balancing Transformers and the Carrier Sets. Armoured H.F. cable should be used. The Co-axial Cable can be directly buried in the ground; however, it is preferable to provide suitable trench from out-door switchyard to the carrier room to lay the Co-axial Cable. Proper Co-axial Cable connections is one of the most important tasks and the connection of the Co-axial Cable to the Cable Connector Plug should be done carefully, as per the special instructions attached. While cutting the Co-axial Cable it should

be noted that at least 1 mt. extra length should be foreseen in order to avoid cable joints due to minor modifications or due to waste while connecting the Co-axial Cable to the Cable end connectors. Till the time the Co-axial Cable ends are not connected to the Co-axial Cable connector these must be sealed by tar to avoid ingress of moisture, which is harmful to the Co-axial Cable. iii)

Connection of Co-axial cable The connection of the C0-axial Cable to the Cable end Socket or to the Cable connector plugs in the Cabinet must be executed according to the attached connection instructions. Line trap is provided with a protective device in the form of surge arresters which is designed and arranged such that neither significant alteration in its protective function nor physical damage shall result from either temperature rise or the magnetic field of the main coil at continuous rated current or rated short time current. The protective device does neither enter into operation nor remain in operation, following transient actuation by the power frequency voltage developed across the line trap by the rated short time current. The protective device is shunt connected to the main coil and tuning device. The lightning arrester is of station class current limiting active gap type. Typically its rated discharge current is 10 kA.

Line traps are equipped with the bird barriers as specified. iv)

Jumper Connections

The overhead conductor is connected by jumpers to the wave trap by using T- Clamps. These connectors are an integral part of the line trap. v) 

General All Indoor equipment should be housed in a well ventilated room having dust free atmosphere.



If the Cabinets are mounted in rows, the distance between the two rails (face to face) should be at least 2 to 3 mtrs. for easy maintenance/testing of the equipment.

11.10

Connection of HF Co-Axial Cable Back to contents page

Instructions for connecting Cable Connector Plugs to HF Co-axial Cable. i) Cut off the cable somewhat longer than needed(according to local conditions), leaving enough slack to make a loop when connecting the cable. ii) Loosen the screw and take the plug to pieces. iii) Put the cone and threaded cylinder over the cable iv) Remove PVC-covering and copper braiding for a length of 20 mm (4/5 inch) v) Cut off PVC covering for an additional length of 6 mm (1/4 inch) vi) Slightly spring open the split section of the plug interior vii) Push the cable into the spring opening of the above part viii)Draw the copper braiding through the two holes in the plug interior piece and solder it to the outside of the plug interior piece

ix) Solder the cable conductor to the plug pin and cut off the part which protrudes. (Do not heat the pin too long because of the polyethylene insulation) x) Slide the threaded cylinder and the cone back into position and tighten the screw xi) Test cable for continuity and short circuit xii) Fasten the cable beneath the connector plug by means of bracket clip, so that the plug is not subjected to any tension. 11.11

Installation of Equipment as per planned system Back to contents page

Installation should be done as per planned system. The equipment allocated for a particular section should not be diverted. This may result in complications at a later stage because of crowded carrier spectrum. 11.12

Defective Modules and Fault Rectification at Site Back to contents page

The defective modules of PLCC equipment are generally repaired at suppliers works unless the nature of defects are minor. It is desired that following procedure may be followed while returning the defective modules to supplier: i)After identification of defective modules, a small label/paper sticker can be pasted on the module frame with “module defective” indication. This helps in identifying the defective parts. Writing by pen or any scratches on the module should be avoided. It would be advisable to give the details of the part failures observed by the maintenance persons for easy checking and rectification.

ii)After identification of the defective modules, these should be securely packed with adequate packing material to avoid transit damage. iii)It is desired that the cabinet nos. of the PLC terminal should be intimated to the supplier/kept in record while sending the defective modules. This will enable quick replacement after receipt of modules duly repaired. iv)Frequency dependent parts viz., filters are normally under

long

guarantee. The modules require accurate adjustment which in turn require sophisticated/accurate measuring set up.

Therefore, it is

essential that these modules are returned to supplier immediately after they are found defective, without any efforts to repair them at site.

DO’S DON’TS & SPECIAL PRECAUTIONS

11.13

Do’s, Don’ts and Special Precautions Back to contents page

i) All the welding included in the manufacture of line traps should be performed by personnel and procedure qualified in accordance with ASME-IX and all the critical welds should be subject to tests as per FQP/LOA as applicable. ii) Terminal Connectors should conform to IS: 5561. iii) Terminal connectors for ACSR single/twin bundle conductor should be suitable for either horizontal or vertical take-off of the conductor. iv) No part of clamp or connector (including hardware) should be of magnetic material. v) All castings of terminal connectors should be free from blow holes, surface blisters, cracks and cavities.

All sharp edges shall be

blurred and rounded off. vi) Connections of line trap should not foul with any other equipment. vii) H.F. cable joints should be avoided to the extent possible. viii)Amphenol type of terminals should be used for H.F. connections. ix) The unbalanced HF cable should be earthed at PLC equipment end only. x) The balanced HF cable should be earthed at both ends. xi) The line traps are packed in wooden crates rectangular in shape and should always be positioned in their vertical state. xii) In pedestal mounted traps, the pedestal with its associated components is normally fixed to the trap.

For proper stability,

pedestal may be apportioned to the top end of the packing crate.

xiii)Line trap should be shifted to erection site very carefully so as to avoid transportation damage. xiv)Line trap should be mounted on the support insulator pedestal and bolted properly. Crane or derrick arrangement should be used for this purpose. xv) Level of the pedestal on 400 kV BPIs is to be checked carefully and grouting bolts should be tightened properly with the required torque. xvi)The body & the internal parts of the line trap should be handled carefully to avoid any damage while placing it on the erected insulator pedestal. xvii)For all copper connections flat Copper strip of specified size is to used. The connections from H.F. point of the Coupling Capacitor to the 3-Elements of the Protective and to the Line Matching Units/Line Matching & Distribution Units/Coupling Filters/Balancing Transformers should be completed as per Drawing. xviii) While completing the copper connection one should ensure that the copper strip connections must be properly tinned by brazing stove and thereafter the same should be painted to avoid rusting or oxidation due to moisture. xix)As suspension hardware is arranged by the erection contractor, care should be taken so that the same is available before the erection work. xx) Before erecting the blocking band of Line Traps are to be checked with respect to requirement of the line. xxi)For interconnection between Protection equipment and Relay Panel the cable required is 10/20 core 1 mm dia Control Cable.

The

length of the cable will depend upon the distance between the Protection equipment cubicle and the relay panel of the distance protection relay. xxii)For

interconnection

between

AF

shift

channel

to

line

unit/teleprinters cable required is 0.6 mm dia, 5-pair telephone cable. xxiii)For interconnection between Carrier set and 4-Wire Group Selector/PAX housed in separate cabinet the cable required is 10/20 - pair 0.6 mm diameter cable. xxiv)For interconnection between PAX and Telephone instrument the cable required is 0.6 mm dia. 10 pair/20 pair or even one pair/2 pair/5 pair telephone cables, depending upon the positions and number of the Telephone Instruments to be connected to the PAX.

CHECK FORMAT

11.14

Check Format Back to contents page

1.

Physical verification of different items done as per specifications, challans, BOQ, MICC etc.

Yes/No

2.

All parts have been checked for any physical damage, discrepancy etc.

Yes/No

3.

In case of any damage/discrepancy same has been reported to supplier/insurance agency.

Yes/No

4.

Corona ring for 400 kV WT has been fitted before lifting the same for erection.

Yes/No

5.

Suspension hardware for WT has been arranged by erection contractor before start of erection.

Yes/No

6.

Blocking bands of line requirements of the line.

w.r.t.

Yes/No

7.

Protective earthing of PLC terminals and panels with the substation earthing has been done.

Yes/No

8.

All hardware accessories, mounting stools including bolt/nuts for fixing Line Trap and insulators are of non-magnetic material.

Yes/No

9.

Impedance point available on coupling device has been checked with respect to available HF cable impedance.

Yes/No

10.

H.F. point of CVT on which the coupling device is not mounted has been earthed.

Yes/No

11.

The remaining, two CVTs have been earthed thro’ coupling device.

Yes/No

12.

Conductor take off from line trap has been checked up with the Line Trap Drawings.

Yes/No

13.

Connection of Co-axial cable to the cable connector plug has been done carefully as per the specified instructions.

Yes/No

14.

About 1m. extra length of Co-axial cable has been provided before cutting.

Yes/No

15.

Co-axial cable ends are kept sealed to avoid ingress of moisture till the time these are not connected to the cable connector.

Yes/No

16.

All indoor equipments are housed in a well lit/ventilated and dust free room.

Yes/No

trap

have

been

checked

17.

Proper face to face distance of cabinets inside the PLCC room is maintained between the two rails for maintenance/testing of equipments.

Yes/No

18.

All suspension hardware to be arranged by the erection contractor have been made available before the erection work.

Yes/No

19.

While completing the copper connections it has been ensured that the copper strip connections are properly tinned by brazing stove and same have been painted to avoid rusting or oxidation due to moisture.

Yes/No

CHAPTER-12 CABLES

___________________________________________________________________________ CHAPTER

TWELVE ___________________________________________________________________________ CABLES Back to contents page

12.0

Introduction Back to contents page

The function of cables in the substation is to transfer power from auxiliary loads and connecting control systems.

Power cables are

manufactured with 1,2,3 or 4 crores. The conductor is either copper or aluminium. The conductor may be either solid or stranded. Each core of the cable is provided with insulation. The insulation may be of PVC or XLPE. Over the core insulation, a sheath of PVC or plastic PVC tape is provided. Protective covering and armour made up of plastic or steel is provided over the sheath. The auxiliary power for substation auxiliaries is supplied through underground cables. The power cables are used for various voltages upto 220 kV. There are several types of power cables, depending on type of insulation and configuration of conductors, shield, insulation, etc. Thus a power cable is made up of the following basic components: i) Conductor ii) Core insulation iii) Sheath (Inner/Outer) iv) Protective covering and armouring. Control cables are used in substations for connecting control systems, measurement, signalling devices and protection circuits rated below

1000 V. They have a copper conductor.

They may have another

rubber insulation or PVC insulation. Control cables have several cores, each having independent insulation. To avoid interference due to straymagnetic fields, the control cables should be properly laid and their sheaths should be properly earthed. Control cables are used for protection circuits, communication circuits. They are generally at low voltage (220 V AC, 110 V AC, 22048 V DC, 110 V DC, 48 V DC, etc.).

Control cables are wired between the

control panels in the control room, and the various equipments in the switchyard.

The

various

measurements,

protection,

control

communication functions are dependent on control cables. The control cables are also laid on cable racks inside the cable trenches. 12.1

Receipt, Inspection and Storage Back to contents page i)

Cable drums are procured in full drum length.

In a typical

substation 1.1 KV grade power & control cables are procured in full drum length of 500m +5%. These cable drums are issued to the switchyard contractor for laying and connecting as per the approved drawings. ii) Cable drums should be unloaded with cranes/chain pulley blocks to prevent any damage. iii) The drums should be checked with the LOA, GR and MICC for the serial no., length, size and make. iv) In case of any discrepancy in size or visible damage to the cable, matter should be immediately brought to the notice of the supplier at the earliest.

v) Drums after visual inspection should be stored preferably in the covered area. In case these are stored in open, proper care and security should be provided to avoid theft/damage to the cable. vi) The cable accessories and hume pipes are supplied by the switchyard contractor.

Site should check these items for any

damage, discrepancy in size and material. 12.2

Cable Laying in Switchyard Back to contents page

Cable laying in switchyard is done by following 2 methods. i) Cable laying in underground (buried trenches). ii) 12.2.1

Cable laying in cable trays.

Cable laying in underground (buried trenches) Back to contents page

The cable trench in which the cable is to be buried under the ground excavated upto the required depth of 1 to 1.2 m or as specified. The bottom of the trench is levelled, freed from stones and sharp edges of rock. A layer 10 cm thick of clean sand is laid at the bottom of the trench. After laying the cable, it is covered with a 10 cm thick layer of sand, where the soil conditions are not good. In other cases soft earth may be used instead of sand. The remaining gap is filled with soft soil and a layer of bricks is usually provided for protection against mechanical damage and for identification of the cable route. In case the cable is laid in pipes, the pipes may be of ceramic/cast iron/galvanised iron/cement/PVC or as per specified material and size. These are used for crossing streets or under railways tracks. The size should be sufficiently large to put in additional cables later if required

so that the cables can be drawn out and replaced without disturbing the earth above. Cable markers/joint markers

at the specified distance enroute the

cable trenches should be provided for cable tracing & direction. 12.2.2

Cable laying in cable trays Back to contents page

i) Cables should be laid as per approved drawings and schemes ii) The cable laying and termination schedule should be checked at site w.r.t. actual conditions.

This will facilitate in checking the

complete coverage of various approved schemes and termination. iii) A cable laying schedule is prepared based on which the size of cable required for various equipments is calculated. The lengths of the cables are also checked at site by actually measuring and necessary changes should be incorporated in the drawings. iv) The length of cable actually required should be more than the actually measured to take care of cable termination in terminal blocks. v) More length will also help in future to take care of cable faults, when some cable is required to be cut and cable joint is provided. vi) The erection contractor based on the actual physical measurements and drawings prepares a cable cutting schedule. The cable cutting schedule is prepared to optimise the cable lengths and minimise wastage. vii) For pulling the cables from drums, rollers are used by placing at about 2 m spacing.

viii)Power and control cables are secured to the separate cables trays. The cable trays carrying power trays are on top tiers whereas the control cables are laid in the trays below. ix) Other cables like coaxial cables are laid separately from power and control cables. x) The power cables are fixed on trays. A clearance of 2d(where d = dia of cable) is maintained from centre to centre. xi) To minimise any damage to cable, the cable ends should be sealed. xii) Proper cable tags for identification should be tied to the cable. The information like cable number, size, length, origin & termination point of cable are to be punched on these tags. xiii)Concrete or steel pipes that are buried at 1 to 1.2 m level below the ground (or as specified) should be laid and cable should be made to pass through these in case the cable crosses the drains, roads or rail track. xiv)All the cable trays, racks & metallic ducts should be grounded by connecting at each end to earth-mat. The section of cable trays should be bridged by copper (or as specified material) jumpers to retain continuity of earthing. 12.3

Cable Termination Back to contents page

i) The cable termination work comprises of fixing, providing clumps, cutting, drilling, fitting and other plumbing works. ii) A cable termination schedule is prepared before starting the cable termination.

iii) Cables are checked for continuity before the termination work.

DO’S DON’TS & SPECIAL PRECAUTIONS

12.4

Do’s Don’ts and Special Precautions Back to contents page

i) Ensure that the cable trench work is complete in all respects and the trenches are clean. ii) Ensure that earth flat running is complete and all welding work inside the trench is completed. iii) During unreeling, laying and termination of cables, sufficient care should be taken to avoid damage to the cables because of twist, kink, sharp bend etc. iv) Cables should be securely fixed to the cable trays. v) Whenever it is required to bend the cable care should be taken so that the standard permissible limits for bending are not crossed. a)

Control cables (1.1 kV) should not be bent below a radius of 10x d

b)

Power cables (1.1 kV) should not be bent below a radius of 12x d (where d = dia of the cable)

i) Each cable and conduit run should be tagged with numbers that appear in the cable and conduit schedule. ii) The tags should be of aluminium with the number punched on it and securely attached to the cable conduit by not less than two turns. Cable tags should of rectangular shape for power cables and of circular shape for control cables. iii) The underground cable markers should project 150 mm above ground and spaced at an interval of 30 meters. They

shall be

located on both sides of road and drain crossings and also at every change in direction.

iv) Cable tags should be provided inside the switchgear, motor control centres, control and relay panels etc. wherever required for cable identification, where a number of cables enter together through a gland plate. v) For drilling of gland plates holes should not be made by gas cutting. vi) Double compression type nickel plated (coating thickness not less than 10 microns) brass cable glands are provided by the Contractor for all power and control cables to facilitate dust and weather proof termination. vii) The cable glands should comprise of heavy duty brass casting, machine finished and nickel plated, to avoid corrosion and oxidation. Rubber components used in cable glands should be of neoprene and of tested quality. viii)The cable (power and control) between LT station, control room, DG set building and fire fighting pump house should be laid in the buried cable trenches. In addition to the above, for lighting purpose also, buried cable trench can be used in outdoor area. ix) Cable route and joint markers and RCC warning covers should be provided wherever required. The voltage grade of cables should be engraved on the marker. x) Cable should be laid on cable racks, in built-up trenches, vertical shafts, excavated trenches for direct burial, pulled through pipes and conduits laid in concrete ducts, run bare and clamped on wall/ceiling/steel structures etc. as shown in the drawings. xi) Cable racks and supports should be painted after installation with two coats of metal primer (comprising of red oxide and zinc

chromate in a synthetic medium) followed by two finishing coats of aluminium paint. xii) Cables should be generally located adjoining the electrical equipment through the pipe insert embedded in the floor. xiii)In the case of equipments located away from cable trench either pipe inserts should be embedded in the floor connecting the cable trench and the equipment or in case the distance is small, notch/opening on the floor should be provided. In all these cases necessary bending radius as recommended should be maintained. xiv)Cabling in the control room should be done on ladder type cable trays. xv) Cables from the equipment to trench should run in GI conduits. xvi)Flexible conduit should be used between fixed conduit/cable trays and equipment terminal boxes, where vibration is anticipated. xvii)Power and control cables should be laid in separate tiers. The order of laying of various cables should be as follows, for cables other than directly buried. xviii)Power cables on top tiers. xix)Control instrumentation and other service cables in bottom tiers. xx) Metal screen and armour of the cable should be bonded to the earthing

system

of

the

station,

as

per

the

approved

drawings/schemes. xxi)Rollers should be used at intervals of about two metres while pulling the cables.

xxii)All due care should be taken during unreeling, laying and termination of cable to avoid damage due to twist, kinks, sharp bends, etc. xxiii)Contractor should remove RCC/Steel trench covers before taking up the work and replace all the trench covers after the erectionwork in that particular area is completed or when further work is not likely to be taken up for some time. xxiv)Contractor should furnish report on work carried out in a particular week/specified period indicating cable numbers, date on which laid, actual length and route, testing carried out, termination carried out in the specified no. of copies. xxv)Tray identification no on each run of trays at an interval of 10 m should be painted. xxvi)In case the outer sheath of a cable is damaged during handling/installation, the same should be repaired to the satisfaction of the site. In case any other part of a cable is damaged, the same should be replaced by a healthy cable. xxvii)Cable drums should be unloaded, handled and stored in an approved manner and rolling of drums should be avoided as far as possible. xxviii)Control cable cores entering control panel/switchgear/MCB/ MCC/ miscellaneous panels should be neatly bunched, clamped and tied with nylon strap or PVC perforated strap to keep them in position. xxix)Tag/ferrule on control cable cores at all termination should be provided as per specification. In panels where a large number of

cables are to be terminated and cable identification is difficult, each core ferrule should include the complete cable number as well. xxx)Spare cores should be similarly tagged with cable numbers and coiled up. xxxi)Cable entry points should be sealed and made vermin and dust proof and unused openings effectively closed. xxxii)Solderless crimping of terminals should be done by using corrosion inhibitory compound. xxxiii) All cable termination should be appropriately tightened to ensure secure and reliable connections. All the exposed parts of cable lugs should be covered. with tape, sleeve or paint.

CHECK FORMAT

12.5

Check Format Back to contents page

1.

Proper unloading arrangement has been made at site Yes/No (Preferably with crane) to unload the packages.

2.

All items have been checked with the packing list, MICC, Yes/No Challans GR etc.

3.

After unloading the visual inspection of the packings has been Yes/No carried out along with the erection contractor and preferably with the manufacturer of the equipment.

4.

Cable drums have been unloaded with crane/chain pulley block to prevent any damage.

Yes/No

5.

Drums have been checked for quantity and damage to cable.

Yes/No

6.

Cable in underground (buried trenches) have been buried Yes/No under the ground upto the required depth of 1 to 1.2 m.

7.

Cable has been laid and all civil works performed as per the Yes/No technical specifications.

8.

Crossing of roads, rail tracks has been done in the Yes/No ceramic/cast iron/GI/ Cement pipe of specified size.

9.

Cable markers/joint markers have been pointed at the Yes/No specified distance enroute the cable trench for cable tracing and direction.

10.

Cable in cable trenches have been laid as per approved Yes/No drawings.

11.

Length of cable actually required is more than the measured Yes/No are to take care of cable termination in terminal block and cable faults in future.

12.

Cable laying and termination schedule has been prepared as per the actual site conditions and actual measurements.

Yes/No

13.

Cables are being laid as per approved cable laying schedule.

Yes/No

14.

A cable cutting schedule has been prepared to optimise the cable lengths.

Yes/No

15.

Cables are being pulled from drums on rollers.

Yes/No

16.

Power and control cables are laid on separate cable trays.

Yes/No

17.

Co-axial cable is laid separately from para & control cable.

Yes/No

18.

A clearance of 2d (where d= dia of cable) is maintained from centre to centre.

Yes/No

19.

Cable ends have been sealed to minimise any damage.

Yes/No

20.

All cable trays, racks and metallic ducts have been grounded Yes/No by connecting each to earth/met.

21.

Sections of cable trays have been bridged by copper jumpers Yes/No to retain continuity of earthing.

CHAPTER-13 CONTROL & RELAY PANELS

___________________________________________________________________________ CHAPTER

THIRTEEN ___________________________________________________________________________ CONTROL AND RELAY PANELS Back to contents page

13.0

Introduction Back to contents page

A substation control room has following provisions and functions: 

Metering and instrumentation



Tap-changer control and control of shunt capacitors for voltage control.



Normal switching function from control room.



Protection of transmission lines, busbars, transformers, reactors, circuit breakers, auxiliaries etc. in the event of abnormal conditions such as faults.



Voice communication with neighbouring power stations and substations by PLC (Power Line Carrier).

The various control panels, protection panels, PLC communication panels, etc. are housed in the control room building of the substation. The relay and control panels are located mainly in the control room of the substation building from where it is possible to supervise and monitor the substation.

The substation can also be provided with

equipment allowing remote control from another substation or loaddespatching centre.

The control room has the following panels

depending upon the local needs: 

Control panels for individual feeder.



Protective relay panels.



Synchronising panels.



Carrier communication panel.



Panel for recording instruments i.e. DR, EL & Fault Locator.

In addition to the above indoor panels, in the control room, the following indoor equipments are installed in the main substation building on one or more floors/ or in other separate buildings. 

MCC ( Main Control)Panel



ACDB



DCDB



Fire-Fighting Control Board



Air Conditioning Control Panel

The ACDB panel in the substation feeds the auxiliary power to switchyard equipments and township. The other panel in control room are Emergency Lighting Distribution Board for feeding the emergency lighting in and around control room. 13.1

Construction Features Back to contents page

i)

The panels are free standing, floor (channel) mounting type and comprise structural frames completely enclosed with specially selected smooth finished, cold rolled sheet steel of specified thickness with front sheet and door frames, sides, door, top and bottom portions.

iii) All doors, removable covers and panels are gasketed all around with neoprene gaskets.

iv) Ventilating louvers in the panels

have screens and filters. The

screens are made of either brass or GI wire mesh. v) Panels have base frame with smooth bearing surface which is fixed on the embedded foundation channels/insert plate. Anti-vibration strips made up of shock absorbing material

are placed between

panel & base frame. vi) Panels are provided with the gland plates at the bottom for cable entry. Construction wise the C&R panels can be divided in two types 13.2

Simplex Panel Back to contents page

Simplex panel consists of vertical front panel with equipment mounted thereon and having wiring access from rear for control panel & either front or rear for relay panels. In case of panels having width more than 800 mm, double leaf-doors are provided. Doors

have handles with

either built-in locking or provided with padlock for closing/locking facility. 13.3

Duplex Panel Back to contents page

Duplex panel are walk-in tunnel type comprising of two vertical front and rear panel sections connected back-on-back by formed sheet steel roof tie members and a central corridor in between.

The corridor

facilitates access to internal wiring and external cable connections. In case of number of duplex panels located in a row side by side, the central corridor is aligned to form a continuous passage. Both ends of the corridor are provided with double leaf doors with lift off hinges.

Doors

have handles with built-in locking

or provided with pad-locks

for closing/locking facility. Separate cable entries are provided for the front and rear panels. 13.4

Receipt and Storage at Site Back to contents page

i) The C&R panels are generally transported in trucks to the site. ii) Panels are transported in vertical position only. iii) At site proper unloading arrangements preferably with crane or chain pulling block are made. iv) After unloading the visual inspection of the panels should be carried out along with the erection contractor and preferably with the manufacturer of the panels. v) The panels, should be checked with the packing list, MICC, Challans GR etc. vi) In case of any discrepancy

of the items from the above

documents/LOA, the same may be intimated to the manufacturer at the earliest. vii) Any type of damage to the panels during transportation or any missing items should also be brought to the notice of the panel supplier or the insurance agency (if required). viii)The panels are sent to the erection site or in store if the site is not ready for the erection. However, the panels should be repacked if these are to be stored for long time. Panels are stored in vertical position only. 13.5

Erection of Panels Back to contents page

i) The site where the panels are to be erected should be ready actually before the panels are brought. ii) The panels should be erected as per the approved general arrangement drawings from POWERGRID. iii) It should be checked that the foundation of the panel is ready in all respect. The foundation frame should also be erected confirming to the necessary drawings. iv) The required level of the foundation/foundation frame etc. should be checked very carefully before the erection work. v) All the panels are to be checked for alignment, verticality etc. The true level is checked using spirit level or water tube. vi) The polythene cover provided by the manufacturer on the panels should not be removed at the erection stage rather it should be retained upto the commissioning stage so as to avoid the dust and scratches on the panels. vii) Earthing of panels is done by the erection contractor for connecting it with switchyard earth mat. 13.6

Mounting on Panels Back to contents page

i) All equipments on (or in) the panels are mounted and completely wired to the terminal blocks ready for external connections. ii) Equipments are mounted such that removal and replacement can be accomplished individually without interruption of service to adjacent devices and the easy access is available without use of special tools. Terminal marking on the equipment shall be clearly visible.

iii) The centre line of switches, push buttons and indicating lamps are not less than 750 mm/specified height from the bottom of the panel. The centre lines of relays, meters and recorders are not less than 450 mm/specified from the bottom of the panel. iv) The centre lines of switches, push buttons and indicating lamps is matched to give a neat and uniform appearance. Like wise the top lines of all meters, relays and recorders is matched. 13.7

Panel Internal Wiring and Equipments in Panels Back to contents page

i) Wiring provided between all electrical devices mounted and wired in the panels and between the devices and terminal blocks for the devices to be connected to equipment outside the panels is done by the panel supplier. ii) When panels are arranged to be located adjacent to each other, all interpanel wiring and connections between the panels is carried out internally. iii) All the internal wiring is securely supported, neatly arranged, readily accessible and connected to equipment terminals and terminal blocks. Wiring gutters & troughs are used for this purpose. iv) Auxiliary bus wiring for AC and DC supplies, Voltage Transformer circuits, annunciation circuits and other common services is provided near the top of the panels running throughout the entire length of the panels. v) Wire termination are made with solderless cirmping type and tinned copper lugs which firmly grip the conductor. Insulated sleeves are provided at all the wire termination’s. Engraved core identification

plastic ferrules marked to correspond with panel wiring diagram are fitted at both ends of each wire. vi) Longitudinal troughs extending throughout the full length of the panels are preferred for inter panel wiring. 13.8

Providing Terminal Blocks Back to contents page

i) All internal wiring to be connected to external equipments is terminated on terminal blocks, preferably vertically mounted on the side of each panel. ii) Terminal blocks are continuous current rating, moulded piece, complete with insulated barriers, stud type terminals with washers, nuts and lock nuts. iii) Terminal

blocks

are

suitable

for

connecting

the

following

conductors/ cable on each side: a) All CT & PT/CVT circuits: (of specified sized cables). b) AC/DC Power supply Circuits : (of specified sized cables). c) All other circuits: (of specified sized cables). iv)

A minimum clearance of 250 mm/.as specified between the first row of terminal blocks and the associated cable gland plate or panel

side

wall,

as

per

the

Terminal

block

mounting

arrangement is adopted. v)

The clearance between two rows of terminal blocks edges should be minimum of 150 mm.

vi)

Mimic diagram is preferably made of anodised aluminium or plastic of approved fast colour material and screwed on to the panel that can be easily cleaned.

13.9

Name Plates and Markings Back to contents page

i) Inside the panels all equipment mounted on front and rear side as well as equipment mounted

inside are provided with individual

name plates with equipment designation engraved. ii) On the top of each panel on front as well as rear side, large and bold name plates are provided for circuit/feeder designation. iii) All front mounted equipments are provided at the rear with individual name plates engraved with tag numbers corresponding to panel internal wiring to facilitate easy tracing of the wiring. iv) The name plates mounted directly by the side of the respective equipments should not be hidden by equipment wiring. v) The name plate ‘inscription’ and size of name plates and letters should be as approved by site Engineer. 13.10

Panels Accessories Back to contents page

i)

Plug Point 240V, Single phase 50 Hz, AC socket with switch suitable to accept 5 Amps and 15 Amps pin round standard plug, is provided in the interior of each cubicle with ON-OFF switch for connection of hand lamps.

ii)

Interior Lighting Panels are provided with a fluorescent lighting fixture rated for 240 Volts, single phase, 50 Hz supply for the interior illumination of the panel during maintenance. The fittings is complete with switchfuse unit and switching of the lighting is controlled by the

respective panel door switch. Adequate lighting with switchfuse unit is also provided for the corridor in Duplex panels. iii)

Switches and Fuses Control panels are provided with necessary arrangements for receiving, distributing, isolating and fusing of DC and AC supplies for various control, signalling, lighting and space heater circuits. The incoming and sub-circuits are separately provided with switchfuse units.

iv)

Space Heater Panels are provided with a space heater rated for 240V, single phase, 50 Hz, AC supply for the internal heating of the panel to prevent condensation of moisture.

13.11

Earthing Back to contents page

i) All panels are equipped with an earth bus securely fixed. ii) When several panels are mounted adjoining each other, the earth bus is made continuous with necessary connectors and clamps for this purpose. iii) Provision is made for extending the earth bus bars to future adjoining panels on either side. iv) Provision is made on each bus bars of the end panels for connecting earthing grid. v) All metallic cases of relays, instruments and panel mounted equipment including gland plates are connected to the earth bus by copper wires of specified size. vi) The colour code of earthing wire is green.

vii) Soldering of earthing wire to terminals with suitable clamp connectors is not permitted.

DO’S DON’TS & SPECIAL PRECAUTIONS

13.12

Do’s Don’ts and Special Precautions Back to contents page

i) Panels should be completely metal enclosed & dust, moisture and vermin proof. ii) Workmanship of the panels should be such as to result in neat appearance, inside and outside with no welds, rivets or bolt head apparent from outside with all exterior surfaces tune & smooth. iii) No equipment should be mounted on the doors. iv) At existing station panels should be matched with other panels in the control room in respect of dimensions, colour, appearance and arrangement of equipments (centre lines of switches, push buttons and other equipments) on the front of the panel. v) Ferrules should fit tightly on the wire and not fall off when the wire is disconnected from terminal blocks. vi) Ferrules in cable should indicate the TB no. of both the ends. vii) All wires directly connected to trip circuit breaker or device should be distinguished by the addition of red coloured unlettered ferrule. viii)Inter-connections to adjacent panels should be brought out to a separate set of terminal blocks located near the slots of holes meant for taking the inter-connecting wires. ix) Arrangements should permit easy inter-connections of adjacent panels at site and wires for this purposes should be looped and bunched properly inside the panels. x) Completeness and correctness of the internal wiring and the proper functioning of the connected equipments should be checked by the erection contractor.

xi) At least 20% spare terminals should be provided on each panel and these spare terminals should be uniformly distributed on all terminal blocks. xii) When semaphore indicators are used for earth switch position they should be so mounted in the mimic that the earth switch close position shall complete the continuity of mimic. xiii)Indicating lamp, one for each feeder, for each bus should be provided on the mimic to indicate bus charged condition. xiv)Control & Relay panels are to be checked with the schematic drawings and Bill of Materials for proper mounting of various equipments and relays. xv) It should be ensured that the erection front is ready for taking up the erection work. xvi)Cable entries to the panels should be from the bottom and through cable glands. xvii)Cable gland plate fitted on the bottom of the panel should be connected to earthing of the panel/station through a flexible braided copper conductor rigidly. xviii)Each instrument and meter should be prominently marked with the quantity measured e.g. KV, A, MW, etc. xix)All relays and other devices should be clearly marked with manufacturer’s name, manufacture’s type, serial number and electrical rating data. xx) Each switch should bear clear inscription identifying its function.

CHECK FORMAT

13.13

Check Format Back to contents page

1.

All items have been checked with the packing list, MICC, Yes/No Challans, GR etc.

2.

After unloading the visual inspection of the panels has been Yes/No carried out along with the erection contractor and preferably with the manufacturer of the panels.

3.

Any type of damage to the panels during transportation or any Yes/No missing items has been brought to the notice of the panel supplier.

4.

In case of any discrepancy from the above documents/LOA Yes/No the same has been intimated to the manufacturer/ insurance agency (as desired).

5.

Proper unloading arrangement has been made at site unload the panels.

6.

Site where panels are to be erected is ready before the Yes/No starting of erection work.

7.

The foundation frame has been erected and checked for Yes/No alignment and level.

8.

Panels during erection on frames have been checked for true Yes/No level by spirit level.

9.

Earthing of panels has been provided.

Yes/No

10.

Wiring on panels is complete upto terminal block

Yes/No

11.

Marking on the equipments is clearly visible.

Yes/No

12.

Equipments have been mounted for easy removal and Yes/No replacement.

13.

Centre line of switches, push buttons indicating lamps is not Yes/No at less than the specified height from the bottom of panel.

14.

All internal wiring is securely supported, neatly arranged, Yes/No readily accessible and connected to equipment terminals and terminal block

15.

Wire termination are made with solderless crimping type and Yes/No tinned copper lugs firmly gripping the conductor.

16.

Proper minimum clearance between 2 rows of terminal blocks Yes/No edges has been provided.

to Yes/No

17.

Mimic diagram has been properly screwed to the panel.

Yes/No

18.

Large and bold name plates have been provided for Yes/No circuit/feeder designation.

19.

Name plates mounted by the side of respective equipments Yes/No are not hidden by equipment wiring.

20.

Proper sized inscription has been done on the name plates

21.

Each switch has been inscripted clearly identifying its Yes/No functions.

22.

Fluorescent lighting fixtures have been provided for the Yes/No interior illumination in the panel

23.

Heaters have been provided inside the panels to prevent Yes/No condensation of moisture

24.

All metallic cases of relays, instruments and panel mounted Yes/No equipment have been earthed

Yes/No

___________________________________________________________________ BIBLIOGRAPHY 1.

ASME Boiler and Pressure Vessel Code – Section-IX.

2.

Rihand Delhi Bipole, HVDC Transmission System – POWERGRID.

3.

Instruction for Erection of Power Line Carrier Communication and Associated Equipments – M/s Asea Brown Boveri.

4.

Electrical Substations Engg. & Practice – S. Rao.

5.

Operation and Maintenance Manual for 216 KV Surge Arrestor – M/s Crompton Greaves Limited.

6.

Construction Manual Part-I substation Construction, Volume-III, Section III : Switchyard Erection SRTS Powergrid.

7.

Technical Specifications Volume-II of Bidding Document for Nathpa Jhakri Transmission System – POWERGRID.

8.

Installation and Service Manual for 420 KV Centre break Isolator by S&S power Switchgear Ltd.

9.

Modern power Station Practice (British Electricity International), Third Edition, Volume K, EHV Transmission.

10.

The Electrical Engineering Handbook, By Richard C. Dorf.

CONSTRUCTION MANAGEMENT DEPARTMENT

User’s Manual Of Construction

Transmission Line (Part-1)

Sub-Station (Part-2)

General Support (Part-3)

Vol. 1 Line Survey

Vol. 2 Env. Mgmt.

Vol. 1 Land & Infrastr.

Vol. 2 Civil Construction

Vol. 1 MB (Procedures & G. Lines)

Vol. 2 Safety

Vol. 3 Soil Investigation & Foundation

Vol. 4 Tower Erection

Vol. 3 Switchyard Ercn.

Vol. 4 Ercn. Of TF, SR & CB

Vol. 3 Contracts Mgmt.

Vol. 4 Budget & Finance

Vol. 5 Stringing

Vol. 5 Aux. Pkgs. (Elect.)

Vol. 5 Labour Regulations