IV Report New

SREE RAMA GOVT. POLYTECHNIC COLLEGE THRIPRAYAR

2016-2017 INDUSTRIAL TRAINING REPORT ON 110KV CHERPU SUBSTATION & 110KV PUDUKAD SUBSTATION Submitted by Sruthy .K .S

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Reg. no: 14030495 Department of electrical and electronics engineering

ACKNOWLEDGMENT I express my sincere gratitude to Mrs. PATHUMMA, Assistant Engineer of Pudukad Sub-Station and to Mr. VIJOY.T.J, Assistant Engineer of Cherpu Sub-Station for their co-operation, encouragement and their valuable advice. I thank The Head of Department of Electrical and Electronics Engineering Mrs. JAYA P.S and also I would like thank Mr. ANILKUMAR.G.S the lecture of our branch, for the immense support and encouragement and express my heartfelt gratitude for their support and guidance. I would like to express my sincere gratitude to everyone who assisted me in making this industrial training successful.

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INDUSTRIAL TRAINING REPORT 2016-2017 GROUP MEMBERS  ANJALI.K.R  ARUL MANU  BIBIN.V.BIJOY  DHIRESH KUMAR.O.K  SRUTHY.K.S

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REPORT Education cannot be contained to the four wall of the class room. Field training is very essential for studying, understanding and appreciating. The subject with this aim industrial visiting was conducted in all polytechnic colleges suggested by the board of technical education. That is why the principal of SRGPTC, Thriprayar arrange an industrial training for duration of two weeks at 110KV Sub-Station, Cherpu and Pudukad running under Kerala State Electricity Board. We the five students of Sree Rama Govt. Poly Technic College, Thriprayar [Sruthy.K.S, Arul Manu, Anjali.T.R, Dhiresh Kumar.O.K, and Bibin Bijoy] had reported to the Cherpu Sub-Station on 9th May 2016 and the Pudukad Sub-Station on 17th May 2016.

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CONTENTS…...  110KV CHERPU SUBSTATION 1. INTRODUCTION………………………………..7 2. SITE SELECTION OF 110KV SUBSTATION…9 3. LAYOUT OF 110KV SUBSTATION……..….…10 4. COMPONENTS OF 110KV SUBSTATION.…...11 i. TRANSFORMER ii. ISOLATOR iii. INSTRUMENT TRANSFORMER iv. LIGHTENING ARRESTOR v. CIRCUIT BREAKER vi. METERING AND INDICATING INSTRUMENTS vii. CAPACITOR BANK viii. SUBSTATION EARTHLING ix. RELAY 5. COMMUNICATION SYSTEM…………………43 6. FIRE FIGHTING SYSTEM………………….......45 7. FUNCTIONING OF THE SUBSTATION………46  110KV PUDUKAD SUBSTATION 1. INTRODUCTION………………………………..56 2. LAYOUT OF THE SUBSTATION……………...57 3. NAME PLATE DETAILS OF EQUIPMENT…...58 4. FIRE FIGHTING SYSTEM……………………...69 5. OPERATING INSTRUCTIONS………………....71  CONCLUSION…………………………………………………..83

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110 KV CHERPU SUB STATION

INTRODUCTION 6

A substation is a part of an electrical generation, transmission, and distribution system. Substations transform voltage from high to low, or the reverse, or perform any of several other important functions. Substations generally have switching, protection and control equipments, and transformers. Substations are of different types. A transmission substation connects two or more transmission lines and a distribution substation transfer’s power from the transmission system to the distribution system of an area. In Kerala, the major substations include one 400 KV sub-station, and seventeen 220 KV substations. The department of Electrical and Electronics Engineering of Sree Rama Govt. Polytechnic College, Thriprayar gives a chance to their students to spend two weeks in industrial companies. This training gives the student the opportunity to see what they have studied and how to deal with practical life. My training program was in the period from 9thMay 2016 at 110kV Cherpu substation for one week. The present day electrical power system is AC i.e.; electrical power is generated, transmitted and distributed in the form of alternating current. The electric power is produced at the power station, which are located at favorable places, generally quite away from the consumers. It is delivered to the consumer through a large network of transmission and distribution. At many places in the line of power system, it may be desirable and necessary to change some characteristics (e.g. Voltage, AC to DC frequency, power factor etc) of electric supply. This is accomplished by suitable apparatus called substation for example, generation voltage (11kV/6.6kV) at the power station is stepped up to high voltage of transmission of electric power. Similarly near the consumer’s localities, the voltage may have to step down to utilization level. This job is again accomplished by suitable apparatus called substation.

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The 110KV substation Cherpu is situated at Perumbillisseri village. At present 110KV substation, Cherpu has two 110KV feeders, normally 1IRJK and 1MADKT feeders. The substation is normally fed from 400KV substation Madakkathara directly which is entering 1st bay in the yard. There is also an alternate feeding from Madakkathara through Irinjalakuda which is entering 2nd bay in the yard. Both feeders may be tied at this substation, according to the power demand at the both ends.The 110KV substation, Cherpu is equipped with 2 nos. of 12.5MVA 110/11KV TELK made transformers and 1 no. of 16MVA 110/33KV TELK made transformer. Substation supplies seven 11KV feeders including station auxiliary.the11KV feeders feeds to the nearby places such as Chenam, Ammadam, Chevoor, Cherpu, Urakam and Karuvanoor.Apart from 110KV bays, there is also a 33KV yard which feeds the 33KV feeders to the Chirakkal and Palakkal substation.

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SITE SELECTION OF 110kV SUBSTATION 110kV substation forms an important link between Transmission network and Distribution network. It has a vital influence of reliability of surface. Apart from ensuring efficient transmission and distribution of power, the substation configuration should be such that it enables easy maintenance of equipment and minimum interruptions in power supply. Substation is constructed as near as possible as the load centre. The voltage level of power transmission is decided on the quantum of power to be transmitted to the load centre. Main points to be considered while selecting the site for grid substation are as follows:  The site chosen should be as near to the load centre as possible.  It should be easily approachable by road or rail for transportation of equipments.  Land should be fairly leveled to minimize development cost.  Source of water should be as near to the site as possible. This is because water is required for various construction activities (especially civil works), earthing and for drinking purposes etc.  The substation site should be as near to the town/city but should be clear of public spaces, aerodromes and military/police installations.  The land should have sufficient ground area to accommodate substation equipments, buildings, staff quarters, space for storage of material, such as store yards and store sheds etc. with roads and space for future expansion.  Set back distances from various roads such as National highways, state highways should be observed as per regulations in force.  While selecting the land for the substation, preference is to be given to Government and over private land.  The land should not have water logging problem.  Far away from obstructions, to permit easy and safe approach termination of high voltage overhead transmission lines. 9

LAYOUT OF THE SUBSTATION

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COMPONENTS OF THE SUBSTATION

A: Primary power line's side B: Secondary power line's side 1. Primary power lines 2. Ground wire 3. Overhead lines 4. Potential or Voltage transformer 5. Disconnect switch 6. Circuit breaker 7. Current transformer 8. Lightning arrestor 9. Main transformer 10. Control building 11. Security fence 12. Secondary power lines

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TRANSFORMER

POWER TRANSFORMER GENERAL The transformer is oil filled equipment conforming to IS: 2026 with ONAN/ONAF. The transformer is provided with fan, pumps, cooler etc. CORE The magnetic circuits is a three limb type. Each limb being mitred with top and bottom yokes. The core is built up with high grade non ageing cold rod grain oriented silicon steel laminations having high permeability and hysterious loss. WINDING Windings are arranged in concentric formation with lowest voltage winding next to core. In case, teritiary winding is arranged then this winding is placed next to the core over LV winding, HV tapping and HV main winding are depending up on requirement of impedence between various winding. TANK The tank is welded mild steel plate construction and is designed to withstand a vaccum in line with stand a vaccum in line with the CBIP recommendation. The tank is coated inside with two coat of yellow oil 12

proof enamel. On the outside it is applied with anticorrosive primer paint and final coat of synthetic enamel to shade No: 631 or 632 of IS-5. COOLING EQUIPMENT The transformer is having either single or mixed cooling of ONAF, ONAN and ONAF by means of heat exchangers, fan and pumps. Fan are provided with wire mesh guards. Fans are mounted either below the radiators and are ground supported or supported on frames at a sides. ONAF-Oil Natural Air Forced Cooling ONAN – Oil Natural Air Natural Cooling CONSERVATOR As the temperature increases or decreases during operation there is a corresponding rise or fall in volume. To account for this as expansion vessel is connected to the transformer tank. The conservator has got a capacity between the minimum to maximum oil level equal to 7.5% of toatal oil in the transformer. DEHYDRATING BREATHER The conservator is connected to outside atmosphere through a dehydrating (silica gel filled)breather to make sure the air in conservator is dry. BUCHHOLZ RELAY The gas and oil actuated (Buchholz) relay is designed to detect faults as well to minimize the propagation of any damage which might occur within oil-filled transformers, capacitors and reactors supplied with oil conservator. The relay is therefore particularly effective in case of: 13

     

Short- circuited core laminations Broken-down core bolt insulation Overheating of some part of the windings Bad contacts Short circuit between phases Earth faults puncture of bushing insulators inside the tank

Furthermore the relay can prevent the development of conditions leading to a fault in the transformer, such as the falling of the oil level owing to leaks, or the ingress of air as a result of defects in the oil circulating system. Operation of buchholz relay Slight faults: When a slight fault occurs in the transformer, the small bubbles of gas, which pass upwards to the conservator, are trapped in the relay housing, thus causing its oil level to fall. As a result, the upper float rotates on its hub and operates the alarm switch, thus operating an external alarm device. Serious faults: When a serious fault occurs in the transformer, the gas generation is violent and causes the oil to rush through the connecting pipe to the conservator. In the relay this oil surge hits the flap fitted on the lower float (located in front of the hole for the oil passage) and causes the rotation of the float itself, thus operating the tripping switch and disconnecting the transformer. The float remains in the trip position even if the oil flow comes to a stop (the reset is done by means of the push-button). The tripping device is regulated in such a way that in transformers having forced oil cooling, the surges resulting from the starting of the oil circulating pump will not cause mal-operation of the relay. An oil leak in the transformer causes the oil level in the relay to fall, thus operating first the alarm (upper) float and then the tripping (lower) float. The ingress of air into the transformer, arising from defects in the oil circulating system or from other causes, operates the alarm float.

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BUSHINGS The bushings consist of a current carrying element in the form of a conducting rod. Up to 33kV ordinary porcelain insulators can be used, above this voltage ratings oil filled or capacitor type bushings are used. Bushing is very important to the overall transformer because without it, conduction would not be possible. The bushings are necessary to complete the conductive energy of the walls that are transferred within the transformer so that they can the move through the medium such as air and gas, including the grounding barriers that each unit is designed with. TERMINALS Very small transformers will have wire leads connected directly to the ends of the coils, and brought to the base of the unit for circuit connection. Larger transformers may have heavy terminals, bus bars or high insulated bushings made of polymers or porcelain. A large bushing can be a complex structure since it must provide careful control of electric field gradient without letting the transformer leak oil. PRESSURE RELIEF VALVE In case of severe fault in the transformer, the internal pressure may build upto a very high level which may built upto a very high level which may result in an explosion of the tank. To avoid such contgency a pressure relief valves is fitted on the transformer. It is a spring loaded and has contact for tripping the transformer ON LOAD TAP CHANGER The on load tap changer consists of diverter switch installed into a pressure tight oil compartment seperated from transformer oil at the tap selector mounted below it. 15

OLTC PANEL FOR TRANSFORMER On load Tap Changer (OLTC) is used with higher capacity transformers where HT side voltage variation is frequent and a nearly constant LT is required. OLTC is fitted with the transformer itself. Multiple tapings from HV windings are brought to the OLTC chamber and contacted to fixed contacts. Moving contacts rotates with the help of rotating mechanism having a spindle. This spindle can be rotated manually as well as electrically with a motor. Motor is connected in such a way that it can rotate in both the directions so as to rotate the OLTC contacts in clockwise and anti clock- wise direction. Two push buttons are fitted on the LCP (local control panel) to rotate the motor and hence the OLTC contacts in clockwise and anti- clockwise direction. This movement of contacts thus controls the output LV voltage of the transformer. So rotating of OLTC contacts with spindle or push buttons in this way is a manual process. In case this process of rotating the OLTC contacts and hence controlling the LV side voltage is to be done automatically then a RTCC (Remote Tap Changer Controller) is installed with the transformer HT Panel. The RTCC sends signals to LCP and LCP in turn rotates the motor as per the signals received from the RTCC OLTC(on load tap changer)is a mechanism used in transformer for changing the tapping position on primary side(HV)of transformer 11kv/66kv the tap changer on the Primary/HV side of the transformer is either raised or lowered to maintain constant 11kv input to transformer. Normally it is raised or lowered in steps of 2.5% of normal KV value. GAS ANALYSIS ON TRANSFORMER OIL Incipient faults in oil filled transformer are usually the result of electrical or thermal excess stress of either transformer oil or insulating materials. 16

It is known as that such excessive stress produced a mixture of gases characteristics of which given an indication of the type of the faults and materials associated with faults. ANALYSIS METHOD Gas Analysis (DGA) 1 2

Gases to be analysed normally Gases to estimate abnormality

3 Gases to estimate deterioration ASSESSING THE TEST RESULT Sl No. 1 2 3

Type of faults

O2 H2,CH4,C2H2,C2H4,C2H 6 CO, CO2, CH4 Decomposable gases in transformer oil CH4,C2H4,H2 H2,C2H2, CH4, C2H4 CO,CO2,H2,C2H4

Over heat oil Arcing of oil Over heat of solid insulating materials 4 Over heat of oil and paper CH4,C2H4,CO,CO2,H2 combination 5 Arcing of oil and paper combination H2,C2H2,CO,CO2,C2H4 SAMPLING OF OIL FROM TRANSFORMER Oil in transformer can be sampled through drain or sampling valve near bottom of the tank. The special care shall be taken not to introduce air, foreign matter or dirty oil into sampling container. For this purpose, first 0.5 to 1 litre of oil from the transformer shall be overflow through the oil container. The oil sampiling method shall be accordance with following figure. The sampled oil shall not be exposed to air before analysis.

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SPECIFICATION TRANSFORMER NO.1 WITH ON LOAD TAP CHANGER Capacity

12.5MVA

Voltage ratio

110000/11000V

Current ratio

65.7/657A

Make

TELK

Type of cooling

ONAN/ONAF

Impedance voltage

9.82%

Vector group

YNyn0

No. of taps

13

Total mass

29060kg

TRANSFORMER NO.2 WITH ON LOAD TAP CHANGER Capacity

12.5MVA

Voltage ratio

110000/11000V

Current ratio

65.7/657A

Make

TELK

Type of cooling

ONAN/ONAF

Impedance voltage

10.52

Vector group

YNyn0 18

No. of taps

13

TRANSFORMER NO.3 WITH ON LOAD TAP CHANGER Capacity

16MVA

Voltage ratio

110000/33000V

Current ratio

84/280A

Make

TELK

Vector group

YNyn0

Mass of core and winding

13100kg

Mass of oil

9600kg

Total mass

33000kg

Type of cooling

ONAN/ONAF

Volume of oil

11160ltr

Impedance voltage

9.768%

STATION AUXILIARY TRANSFORMER

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Auxiliary transformer is used to deliver required AC voltage to the substation. Here we use 1100/440V 160 KVA 3 PHASE transformer. Here the 11KV on the primary sidestep down to 440V.And give to the substation for its working and some general purposes. The supply to the battery charger is taken from auxiliary transformer. A Low Tension panel is provided on the control room. The low tension panel delivers the supply for the control room. SPECIFICATION Capacity

160KVA

Voltage ratio

11000/433V

Current ratio

8.39/213.33A

Make

KEL

Type of cooling

ONAN

% impedance

4.32%

Total weight

829kg

Core & winding weight

209kg

Frequency

50Hz

No. of phases

3

Oil in litres

235l

Max. Temperature rise in oil

45°C

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ISOLATOR

In order to disconnect a part of system for maintenance and repair, isolators are used. It is a knife switch designed to open a circuit under no load. If isolators are to be opened, the Circuit Breaker connected must be opened first. Otherwise there is a possibility of occurrence of a spark at the isolator contacts. After repair, first isolators are closed and then Circuit Breaker. There are two types of isolatorsLine isolators and Bus isolators. For bus isolators, there is no earth switch. During maintenance works the line isolator contacts are opened, so that the three phases trip simultaneously. For the ease of earthing, dead weights are provided at the end of earthing arm.

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SPECIFICATION LINE ISOLATOR OF 110kV FEEDERS Type

DB

Voltage

110KV

Current

800A

Impulse

550 KV

Short time current for 3 seconds 31.5 KA Frequency Constant voltage

50Hz 110V DC

BUS ISOLATOR OF 110kV FEEDERS Type

DB

Voltage

110kV

Current

1250A

Impulse withstand

550kV

Short time current for 1 sec

2kA

Constant voltage

110V DC

BUS COUPLER ISOLATOR Type

DB

Voltage

110kV

Current

1250A 22

Impulse withstand

550kV

Short time current for 1 sec

2kA

Constant voltage

110V DC

INSTRUMENT TRANSFORMERS Instrument transformers means current transformer & voltage transformer are used in electrical power system for stepping down currents and voltages of the system for metering and protection purpose. Actually relays and meters used for protection and metering, are not designed for high currents and voltages. High currents or voltages of electrical power system cannot be directly fed to relays and meters. CT steps down rated system current to 1 Amp or 5 Amp similarly voltage transformer steps down system voltages to 110V. The relays and meters are generally designed for 1 Amp, 5 Amp and 110V.

CURRENT TRANSFORMER

A CT is an instrument transformer in which the secondary current is substantially proportional to primary current and differs in phase from it by ideally zero degree. Current transformers are used for both metering and protection purposes. Depending up on the type of the protections 23

adopted, number of secondary cores required will be decided. All 11kV feeders requires 2 core CT for metering and protection. All 11kV banks, 66kV lines and 110kV lines and 110/33-11kV and 66/11kV power transformers requires 3 core CTs for metering, primary protection (distance protection for lines and differential protection for transformers) and backup protection(over current and earth fault protection).220kV class CTs are of 5 cores for metering, primary protection, backup protection and 2 cores for bus bar protection (main and check zones).Accuracy class of each secondary core differs of depending upon the type of protection. If the type of protection is same then the class of such cores will be same. While ordering the accuracy class, VA burden, and instrument safety factor (ISF-for metering core), accuracy limiting factor (ALF- for backup protection core), knee point voltage, excitation current and Rct for primary protection cores will be specified.  Metering core: Accuracy class( 0.2,0.5), burden-VA and ISF  Backup protection core: Accuracy class (5P10,5P15,5P20), Burden and ALF  Primary protection: Accuracy class (PS), knee point voltage, magnetizing current Io and Rct.  5P10 means- when current is 10times the rated secondary current, the accuracy should not exceed 5% at rated burden. Similarly 5P15 and 5P20. Here P stands for protection.  PS-protection for special purpose.  Knee point voltage (VK) - means the voltage at which the CT cor saturates. It is defined as the voltage at which for an additional increase in 10% voltage, there will be 50% increase in magnetizing current. CTs can be selected as single ratio or multi ratio CTs. For single ratio CTs there are only two secondary terminals for each core (S1 and S2). If multi ratio CTs are required, there will be required number of tapings in 24

each secondary core and they will be marked as S1-S2-S3-S4 etc. To identify the core, each secondary terminal will be marked as 1S1-1S2, 2S1-2S2, 3S1-3S2 etc. SPECIFICATION CURRENT TRANSFORMER ON 110kV FEEDERS Highest system voltage

123kV

Current ratio

400-200-100/1-1-1-1A

Short time current

31.5KA for 1 sec

Frequency

50 Hz

Insulation level

230/550Kv

Total creepage distance

3075mm

Total weight

350kg

Quantity of oil

105ltrs

CURRENT TRANSFORMER OF TRANSFORMER NO.1 Highest system voltage

123kV

Current ratio

600-300/1-1

Frequency

50Hz

Oil weight

90kg

Total weight

590kg

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CURRENT TRANSFORMER OF TRANSFORMER NO.2 Highest system voltage

123kV

Current ratio

600-300/5-5

Frequency

50Hz

Oil weight

90kg

Total weight

590kg

Short time current

31.5KA for 1 sec

CURRENT TRANSFORMER OF TRANSFORMER NO.3 Highest system voltage

123kV

Current ratio

400/1-1-1-1

Frequency

50Hz

Oil weight

90kg

Total weight

590kg

Short time current

25kA for 1 sec

Insulation level

230/550kV

CURRENT TRANSFORMER OF 11kV INCOMER Highest system voltage

15kV

Current ratio

350-175/5-5

Frequency

50Hz

Short time current

25kA for 1 sec 26

CURRENT TRANSFORMER OF 33kV INCOMER Highest system voltage

36kV

Current ratio

400-200/1-1-1-1

Frequency

50Hz

Short time current

25kA for 1 sec

Total weight

125kg

POTENTIAL TRANSFORMER

A Voltage Transformer theory or Potential Transformer theory is just like theory of general purpose step down transformer. Primary of this transformer is connected across the phases or and ground depending upon the requirement. Just like the transformer, used for stepping down purpose, potential transformer i.e. PT has lowers turns winding at its secondary. The system voltage is applied across the terminals of primary winding of that transformer, and then proportionate secondary voltage appears across the secondary terminals of the PT. The secondary voltage 27

of the PT is generally 110V. In an ideal Potential Transformer or Voltage Transformer when rated burden connected across the secondary the ratio of primary and secondary voltages of transformer is equal to the turns ratio and furthermore the two terminal voltages are in precise phase opposite to each other. But in actual transformer there must be an error in the voltage ratio as well as in the phase angle between primary and secondary voltages. SPECIFICATION POTENTIAL TRANSFORMER OF 110kV FEEDERS H.S.V 132KV Insulation level 230/330KV Frequency 50Hz Oil quantity 180 ltr Make BHMEL Primary voltage 110kV/1.732 Secondary voltage 110V/1.732

LIGHTNING ARRESTER

Whenever an incoming comes to a substation, initially the line is connected through a lightning arrester. This is for the protection of the station. Generally a lightning arrester seems like a set of insulators 28

connected together with a ring in the top. This ring is called grading ring. The purpose of grading rings is that in case of heavy voltage surges the charge is distributed uniformly through the ring and then the discharge occurs. An ammeter is connected with the maximum current passed through it. The ammeter is reset. The ammeter in the arrester carrying the topmost conductor will have maximum current passing through it. Metal Oxide Varistors Metal Oxide Varistors have been used for power system protection since the middle of 1970’s. The typical lightning arrestors also known as surge resistors have a high voltage terminal and a ground terminal. When a lightning surge or switching surge travels down the power system to the arrestor, the current from the surge is diverted around the protected insulation in most cases to the earth. SPECIFICATION LIGHTENING ARRESTOR OF 110KV FEEDER Rated voltage : 96 kV Rated frequency : 50Hz Discharge current : 10 kA Maximum operating continuous voltage : 81Kv Pressure relief current : 40 kA Type : Meta over Operating voltage

81KV

CIRCUIT BREAKER Circuit breakers have an in built fixed electric current load capacity which when breached causes automatic circuit shutdown. It basically detects the fault condition like a short or over load in the circuit, interrupts the continuity, and immediately stops the current flow. This safety feature makes insulation of a circuit breaker and essential part in an electric circuit. Overloading in an electrical circuit occurs when the wires are forced to carry and conduct an electric charge more than their capacity. This causes the wires to heat up and results in insulation 29

breakdown and an electric fire. Short circuit occurs when two points in the circuit having different potential accidentally come in contact. This causes unwanted current flow from one node to another which may result in excessive heating, circuit damage, explosion or even fire. Therefore, circuit breakers are used to protect the circuit from unwanted consequences of wire overloading and accidental short-circuiting. CIRCUIT BREAKING MECHANISM Generally, a circuit breaker panel consists of a switch and a moving, conductive contact plate which moves with the switch. When the switch is on an ‘ON’ position, the contact plate touches a stationary plate which is connected to the circuit so that the electric current can flow. But when the switch is in the ‘OFF’ position, due to the overloading or short circuit, the contact plate moves away from the stationary plate and the circuit gets opened and the electric current ceases to flow. Though most circuit breaker has common features in their operation, the mechanism may vary substantially as per the voltage class, current rating and type. In low voltage circuit breakers, when a fault condition is detected, it is rectified within the breaker enclosure, whereas in those meant for large currents or high voltages, special pilot devices like relays are arranged to sense the fault current and rectify it by employing trip opening mechanism. SF6 CIRCUIT BREAKER

110 kV circuit breakers of the substation are SF6 gases CB of make Crompton greaves. The three phases have their own mechanism and air reservoir interconnected pneumatically operated. The control panel is mounted in the middle phase. The pneumatic operating mechanism is 30

operated by compressed air for opening and by spring force for closing. Hence it is important to monitor the air pressure. The breaker can be switched on or off by operating the control switch in control panel in remote mode. Its closing is by spring action and tripping is in air. Each CB has an air tank in which pressure is maintained at 15kg/cm2. If pressure goes below this a rotary compressor is automatically activated. Pressure of SF6 is continuously monitored. SF6 being costly, is filled separately in each CB. The gas can be reconditioned after each operation. Operation mechanism is through air, which is being stored in a closed tank. SPECIFICATION Rated voltage

: 145 kV

Normal current

: 3150A

Frequency

: 50 Hz

Lightning impulse withstand voltage

: 650kV

Duration of short circuit

: 3s

First pole to clear factor

: 1.5

Short Circuit Breaker Current (Symmetrical) : 40 kA Short Circuit Breaker Current (Asymmetrical) : 44.8kA Short circuit making current

: 100kAp

Operating Sequence

: 0-0.3s-CO-3min-CO

SF6 gas pressure at 20°C (abs)

: 0.74mpa

Total mass of SF6 gas (Kg)

: 12 31

VACCUM CIRCUIT BREAKER

A vacuum circuit breaker is such kind of circuit breaker where the arc quenching takes place in vacuum. The technology is suitable for mainly medium voltage application. For higher voltage Vacuum technology has been developed but not commercially viable. The operation of opening and closing of current carrying contacts and associated arc interruption take place in a vacuum chamber in the breaker which is called vacuum interrupter. The vacuum interrupter consists of a steel arc chamber in the centre symmetrically arranged ceramic insulators. The vacuum pressure inside a vacuum interrupter is normally maintained at 10– 6 bar. The material used for current carrying contacts plays an important role in the performance of the vacuum circuit breaker. CuCr is the most ideal material to make VCB contacts. Vacuum interrupter technology was first introduced in the year of 1960. But still it is a developing technology. As time goes on, the size of the vacuum interrupter is being reducing from its early 1960’s size due to different technical developments in this field of engineering. The contact geometry is also improving with time, from butt contact of early days it gradually changes to spiral shape, cup shape and axial magnetic field contact. The vacuum circuit breaker is today recognized as most reliable current interruption technology for medium voltage system. It requires minimum maintenance compared to other circuit breaker technologies. 32

WORKING OF VACUUM CIRCUIT BREAKER The main aim of any circuit breaker is to quench arc during current zero crossing, by establishing high dielectric strength in between the contacts so that reestablishment of arc after current zero becomes impossible. The dielectric strength of vacuum is eight times greater than that of air and four times greater than that of SF6 gas. This high dielectric strength makes it possible to quench a vacuum arc within very small contact gap. For short contact gap, low contact mass and no compression of medium the drive energy required in vacuum circuit breaker is minimum. When two face to face contact areas are just being separated to each other, they do not be separated instantly, contact area on the contact face is being reduced and ultimately comes to a point and then they are finally detouched. Although this happens in a fraction of micro second but it is the fact. At this instant of de-touching of contacts in a vacuum, the current through the contacts concentrated on that last contact point on the contact surface and makes a hot spot. As it is vacuum, the metal on the contact surface is easily vaporized due to that hot spot and create a conducting media for arc path. Then the arc will be initiated and continued until the next current zero. At current zero this vacuum arc is extinguished and the conducting metal vapour is re-condensed on the contact surface. At this point, the contacts are already separated hence there is no question of re-vaporization of contact surface, for next cycle of current. That means, the arc cannot be re-established again. In this way vacuum circuit breaker prevents the reestablishment of arc by producing high dielectric strength in the contact gap after current zero. There are two types of arc shapes. For interrupting current up to 10kA, the arc remains diffused and the form of vapour discharge and cover the entire contact surface. Above 10kA the diffused arc is constricted considerably by its own magnetic field and it contracts. The phenomenon gives rise over heating of contact at its centre. In order to prevent this, the design of the contacts should be such that the arc does not remain stationary but keeps travelling by its own magnetic field. Specially designed contact shape of vacuum circuit breaker make the 33

constricted stationary arc travel along the surface of the contacts, thereby causing minimum and uniform contact erosion. SPECIFICATION Rated voltage

: 11kV

Rated current

:

400A

Breaking capacity : 26.24 kA Making capacity

:

Short time current :

65.6 kA 26.24A, 3 sec

BATTERY AND BATTERY CHARGER The station DC source is facilitated through battery of 400 Ah capacities and 200 Ah capacities. The 400 Ah battery bank no 1 is fed through the battery charger from the main control room. This is of 110kV, 50 A capacities. The second 400Ah battery bank has the same capacity. 200 Ah bank is fed through the battery charger located in the old control room. This is of 110kV, 15 A capacities. This feeds only 11kV cubicles located in the old control room. 110 volt supply is always provided as a standby as there is possibility of power failure in station. At this time also the tripping in case of fault should continue; for this the 80V DC Supply is very essential. 55 batteries each of 2 volt are provided giving a total of 110 V. In some area the required voltage is less; in such cases the batteries used also should be less. The batteries are lead acid cells and have sulphuric acid as its electrolyte with lead electrode along with spongy lead in between. They have 400Ah capacity i.e. they can supply a current of 400A for a time of 1 hour. So it can be used to supply 200A at intervals of 2 hours. This voltage always provided in parallel with the AC supply. It can be used in case the AC fails. The batteries can be charged in 2 modes, float charging and boost charging. Float charging is used when AC is present and Boost charging is used when the battery is in the back up mode. Battery is regularly checked in the substation to 34

check the acidity of Electrolyte. A hydrometer is used to measure the same. To measure the voltage there is the centre zero voltmeter.

METERING AND INDICATING INSTRUMENTS There are several metering and indicating instruments installed in the substation such as ammeters, voltmeters, energymeters, power factor meter etc. to maintain watch over the circuit quatities. The instrument transformers are invariably used with them for satisfactory operation.

CAPACITOR BANK A capacitor bank is a grouping of several identical capacitors interconnected in parallel or in series with one another. These groups of capacitors are typically used to correct or counteract undesirable characteristics, such as power factor lag or phase shifts inherent in alternating current (AC) electrical power supplies. The energy storing characteristic of capacitors is known as capacitance and is expressed or measured by the unit farads. This is usually a known, fixed value for each individual capacitor which allows for considerable flexibility in a wide range of uses such as restricting DC current while allowing AC current to pass, output smoothing in DC power supplies, and in the construction of resonant circuits used in radio tuning. These characteristics also allow capacitors to be used in a group or capacitor bank to absorb and correct AC power supply faults. The use of a capacitor bank to correct AC power supply anomalies is typically found in heavy industrial environments that feature working loads made up of electric motors and transformers. This type of working load is problematic from a power supply perspective as electric motors and transformers represent inductive loads, which cause a phenomenon known as phase shift or power factor lag in the power supply. The presence of this undesirable phenomenon can cause serious losses in terms of overall system efficiency with an associated increase in the cost of supplying the power. The use of a capacitor bank in the power supply 35

system effectively cancels out or counteracts these phase shift issues, making the power supply far more efficient and cost effective. The installation of a capacitor bank is also one of the cheapest methods of correcting power lag problems and maintaining a power factor capacitor bank is simple and cost effective. In Cherpu Substation, capacitor bank is rated for 123kV, 25 MVR consisting of 42 units of 10.14kV, 596.23 kVAR internal fuse capacitor units arranged in double star configuration.

SUBSTATION EARTHLING The earthling system of this substation has buried horizontal mesh of steel rods and vertical electrodes or spikes welded to the mesh. Further, the vertical risers and the galvanized steel grounding strips or copper bare act are connected between the grounding mesh and the points to be grounded. The conventional criterion of low resistance and low current earth resistance measurement continues to be in practice for substations up to 220 kV. Earthling connections are galvanized steel strips or electrolytic copper flats or strips/ stranded wires or cables/ flexible. These are employed for final connection between earthling riser and the points to be grounded. For transformer neutral/ high current discharge paths copper strips or stranded wires are preffered.

DIFFERENT EQUIPMENTS AND GROUND CONNECTIONS Apparatus Parts to be earthed Method of connection 36

Power transformer

Transformer tank

Connect the earthing bolt on transformer tank to the station earth.

High voltage circuit breaker

Operating mechanism, frame

Connect the earthing bolt on the frame and the operating mechanism of Circuit breaker to earthing system

Potential transformer

Potential Transformer tank, LV neutral

Connect the transformer earthing bolt to earthing system. Connect LV neutral of phase lead to case with flexible copper conductor

Current transformer

Secondary winding Weld the isolator base and frame, connect it to the metal case bolt on the operating mechanism, base plate and station earth

Isolator

Isolator frame, operating mechanism, bed plate

Weld the isolator base frame, connect it to the bolt on the operating mechanism, base plate and station earth.

RELAYS 37

Relay functions as a sensing device, it senses the fault, and then determines its location and finally it sense tripping command to the circuit breaker. The circuit breaker after getting the command from the protective relay disconnects the faulted element. From this, we can say that the protective relays are the brain of the scheme. The function of a relay is mainly incorporated in the control panel section of the substation. A protective relay is mainly incorporated in the control panel section of the substation. The relay detects the abnormal condition such as voltage, current, frequency, phase angle and temperature. The substation has control panels for its incoming as well as outgoing feeders and each control panel has various relays. The different types of relays which are used here are  Over current relay  Earth fault relay  Restricted earth fault relay  Differential relay  Distance relay OVER CURRENT/ OVER VOLTAGE /OVER POWER RELAY

The relay activates when current exceeds the permissible limits. It will be connected to the circuit breaker in case of any fault due to over current. The relay acts and activates the circuit to the breaker hence 38

tripping the breaker. DC supply is always given to the relay as it should trip even if there is an interruption in the power supply. DIFFERENTIAL RELAY

The relay is activated at difference in current flowing through the relay. In case of equipments like CT the relay is connected in between the equipments. In normal conditions the current through the relay is the same as the equipment current but when any fault occurs in the line enclosed ten there is a rise in current through the relay at the fault side above that which is on the other side. This activates the relay, tripping occurs. DISTANCE RELAY

It is a special type of relay used to know at which place the line has failed. The lines are divided into zones. The relay will indicate the rough 39

distance between the station and the point at which the breaking has occurred. The connection to the main relay is made through an auxiliary relay. This relay is very helpful in remote areas. RELAY COORDINATION To provide proper backup protection following points are to be considered.  Current transformer ratio used.  Fault level of the station at each voltage class.  Current setting adopted.  Time delay to be adopted as a coordination part.  Type of relay characteristics used- 3 seconds curve or 1.3 seconds curve. Normally 3 seconds curve is used.  The relay operating time depends upon the current setting, time setting and the magnitude of the fault current.  Relay will operate in time which is multiple of time delay setting and the Time Setting Multiplier (TSM) required for a particular magnitude of fault current from 3 seconds curve.  If the fault secondary current is 5 Amps, then the time multiplier from the curve will be 4.3.  For a time delay of 0.1 seconds and for a secondary fault current of 5 Amps, the relay operating time will be 4.3*0.1 seconds (0.43seconds)

Table shows the approximate Time Setting Multiplier(TSM) to be considered for K(PSM) Times Is (secondary fault current) as per 3 seconds curve, K(PSM) TSM K(PSM) TSM K(PSM) TSM Upto 2 10.0 4.30-4.50 4.40 10.01-11.00 2.90 40

2.01-2.30 2.31-2.50 2.51-2.80 2.81-3.00 3.01-3.30 3.31-3.50 3.51-3.80 3.81-4.00 4.01-4.30

8.30 7.60 6.70 6.20 5.70 5.50 5.30 5.00 4.70

4.51-5.00 5.01-5.30 5.31-5.50 5.51-5.80 5.81-6.00 6.01-7.00 7.01-8.00 8.01-9.00 9.01-10.00

4.30 4.20 4.00 3.90 3.80 3.60 3.30 3.20 3.00

11.01-12.00 12.01-13.00 13.01-14.00 14.01-15.00 15.01-16.00 16.01-17.00 17.01-20.00 20.01-30.00 30.01-50.00

2.80 2.70 2.60

RESTRICTED EARTH FAULT RELAY

The main earth fault protection is provided by the restricted earth fault current stage ∆ 10, operates instantaneously, when the differential current exceeds the set start value of the restricted earth fault stage. The restricted earth fault stage operates exclusively on earth faults inside the area of protection. The area of protection is limited by the phase current transformers and the current transformer of the neutral earthing circuit. The operation of the restricted earth fault stage on faults outside the area of protection is prevented by a stabilizing resistor, which is connected in series with the matching transformer of the relay. The operation of the restricted earth fault stage exclusively on faults inside the area of protection is based on the fact, that the impedance of a transformer decreases as the transformer is saturated. The reactance of the excitation circuit of a fully saturated transformer is 41

zero and in these cases the impedance is composed purely of the resistance of the coil. Under the influence of the stabilizing resistor in the differential current circuit the secondary current of the non saturated transformer is forced to flow through the secondary circuit of the saturated transformer. NON DIRECTIONAL OVERCURRENT EARTH-FAULT RELAY The non directional over current earth fault relay is a secondary relay device to be connected to the current transformers of the feeder to be protected. The three phase over current unit and the non directional earth fault unit continuously measure the phase current and the neutral current of the protected feeder. In fault situations, these units initiate external auto reclose functions or trip the circuit breaker depending on the selected protective scheme. When a phase current exceeds the starting value of the low set over current unit, the unit starts, simultaneously starting the corresponding timing circuit. When the set operating time has elapsed, a circuit breaker tripping command is delivered. Correspondingly the high set stage of the over current unit starts when its starting value is exceeded, starting its timing circuit and performing a tripping when the set time has elapsed.

COMMUNICATION SYSTEM WAVE TRAP

42

Wave trap is also known as line trap. It is an instrument used for tripping of the wave. The function of this trap is that it traps the unwanted waves. Its shape is like that of a drum. It is connected to the main incoming feeder so that it can trap the waves which may be dangerous to the instruments in the substation. The wave trap traps the high frequency communication signals sent on the line from the remote substation and diverting them to the telecom / tele protection panel in substation control room through the coupling capacitor and LMU. This is relevant in Power Line Carrier Communication (PLCC) systems for the communication among various substations without dependence on the telecom company network. The signals are primarily tele protection signals and in addition, voice and data communication signals. Line signals sent on the line from the remote substation and diverting them to the telecom / teleprotection panel in the substation control room. The wave trap offers high impedance to the high frequency communication signals thus obstructs the flow of the signals to the substation bus bars. If they were not to be there, then signal loss is more and communication will be ineffective or probably impossible. COUPLING CAPACITOR Serves as the interlink element between high voltage line and low voltage RF carrier equipments. It essentially offers very high impedance

43

the LMU. If CVT is provided instead of PT, it serves the purpose of coupling capacitor.

LINE MATCHING UNIT The LMU consists essentially of an impedance transformer, the primary and secondary winding of which are insulated from each other to withstand a voltage of 10kV. It serves to match characteristics impedance of coaxial cable (125ohm) to that of HV line(600ohm)

DRAINAGE COIL Serves to the ground 50Hz leakage current through CC to earth, thus preventing accumulation of charge on the LV side of capacitor which would result in setting of LA. The coil offers high impedance to the RF signals. The protective devices serves to protect PLCC equipments and personnel from danger through leakage of HV i.e, short circuits or flash over occurring on the coupling capacitor. Earth switch is kept open for normal operating conditions and closed if any work to be done on the communication equipment. It is to be ensured that the drainage coil is properly earthed.

COAXIAL CABLE Serves as an interconnecting cable between the LMU& PLCC set.

FIRE FIGHTING SYSTEM 44

Fire is started or begins at a hot spot and spread along the combustible materials to neighboring area subject to the availability of three essentials. 1. Combustible materials 2. Air and oxygen 3. Heat and local temperature rise Fire extinguishing techniques aim at rapidly removing one or two or all the three essentials mentioned above. FIRE EXTINGUISHING METHODS 1. Cooling- removal of heat 2. Smoothening-removal of oxygen supply 3. Starving- removal of combustible material supply 4. Breaking or interrupting chain reaction- separating combustible material from ongoing fire. The 110kV substation Cherpu is equipped with the following types of fire fighting equipments. 1. 2. 3. 4. 5.

Fire bucket filled with sand Carbon dioxide 6.8*2kg Carbon dioxide 4.5kg DCP 5kg Form type91

7 Nos 4 Nos 5 Nos 5 Nos 6 Nos

OPERATION OF FIRE FIGHTING EQUIPMENTS Carbon dioxide Fire Extinguisher 1. Keep the extinguisher upright and hold firmly in hand. 2. Remove safety pin and turn the wheel anti clockwise 3. Direct discharge at the base of flame in a sweeping motion Dry Chemical Powder Fire Extinguishers (catridge type) 1. Hold upright and remove safety clip. 45

2. Strike knocks with palm of hand. 3. Direct jet to the base of fire. Dry Chemical Powder Fire Extinguisher 1. Hold upright and remove safety clip. 2. Hold nozzle in hand and strike knob. 3. Direct discharge to the base of the fire. Chemical Form (9 Liters) (Inverted type of fire extinguisher) 1. Take the extinguisher to the scene of fire. 2. Pull the T handle forcedly and turn right hand side. 3. Shake well, turn upside down and direct jet to the base of flames.

FUNCTIONING OF THE SUBSTATION RESPONSIBILITIES AND DUTIES 1. Operating crew of substation comprises of one Assistant Engineer as operator and one Overseer as Shift Assistant. Operator on duty shall carry out all the operations required for normal functioning of the substation as per the directions followed. 2. Sub Engineer (Electrical/Maintenance) attends to all maintenance work connected with lines and equipments of substation including routine and breakdown maintenance. He will assist the AE in the preparation of monthly returns and allied Db works. 3. Station Engineer holds overall charge of the substation. OTHER DUTIES OF AN OPERATOR

46

1. Ensure that the control room, switch yard and premises are kept neat and tidy. 2. Keep a constant watch over the equipments and report any abnormalities to the station engineer/ assistant engineer when they are unable to handle the problem themselves. 3. Check all the equipments for any change from normal before taking charge. 4. Go through the operator’s diary, message book and P.W register and keep him post up to date about operational position before starting each shift. 5. Make entries in the tripping register, PW register, interruption register and register of phone calls promptly. 6. Check availability of DC supply in the control panels on taking charge. 7. Take hourly/ half hourly readings and post in log. 8. Arrange watering of earth pits daily. 9. Be familiar with the areas fed by the outgoing 11kV feeders and also possible inter connections between feeders and substations and back feeding possibilities. 10. Maintain voltage within prescribed limit: 11kV (between 10.8 and 11.0) 33kV (between 31 and 33) 11. Take the battery charger charging current and station DC voltage between positive and negative terminals, between positive and earth terminals and between negative and earth terminals during each shift. 12. When a feeder trips out, first recharging should be done after 5 minutes, second recharging after another 5 minutes (it is optional). If the feeder still does not stand, it should be declared as faulty. In case of obviously serve fault, second trial charging can be dispensed with.

47

13. Whenever the feeder declared as faulty, intimate the officer in charge of the feeder. In case the officer in immediate charge could not be contacted, inform the next higher officer available. Inform also the station engineer/ assistant executive engineer. 14. After every auto trip alarm, cancel audible alarm first, note down the indications and then reset the relays. 15. Whenever the feeder is charged, check the voltage and current in all phase. 16. In case of doubt in any operation, request for instructions from the station engineer. 17. Operator will be responsible for maintaining station water supply, arranging switching of switch yard and station lights. 18. Operator will be responsible for tools kept in the control room as well as the wiring drawings and instruction books. 19. They should familiar with the emergency hand operation of the circuit breakers, tap changers etc. produce to be adopted in case of fire accidents, first aid, artificial respiration, safety procedures. 20. The operator should have a detailed knowledge of 110kV feeding arrangement and an alternate source of supply in case of normal feeding is failed.

OPERATIONS IN GENERAL The following operating instructions may be strictly followed for the smooth operation of the substation: 1. The operator, taking over the shift charge shall record the time of taking over the duty with name and signature. He / She shall also record the name of shift assistant in the diary and log book.

48

2.

Handover the charge with clear explanation in brief regarding the substation and feeders such as PW/IC/NBC in force, trouble noted in any of the equipments etc. Handing over time and dated signature with the name of the relieving operator should invariably be recorded.

3. An operator should primarily check protective and alarm circuits of the individual feeders and also the control supply system including the battery system. Then the overall inspection of the control room and yard equipments should be conducted. Check and confirm the reliability of emergency lights and accessibility of fire fighting equipments. 4. Read carefully previous operations and make a thorough picture regarding the substation feeder positions. Record all entries with time and sequence of operations performed. The tripping and any major events requiring special attentions should be recorded in red ink and scheduled interruptions like switch off and permit to work should be recorded in green ink.

5. Message book and phone call register are to be maintained by the operator on duty. Phone message received and transmitted shall be recorded with date and time and confirm the authenticity of the person at the other end. Confirm that the messages are communicated to the right person to whom it is intended and act according to the seriousness of the matter contained therein. 6. Visit the yard frequently and watch the various equipments and their functions carefully. 7. Promptly record hourly and half hourly readings with utmost care. 49

8. The operator on duty shall see that the substation equipments and panels in the control room are kept clean. 9. Station clock timings should be checked and corrected if necessary at 3pm on every day, with 220kV substation Madacathara. 10. Check the specific gravity and the cell voltage of the pilot cells of the station battery and record them in the log sheet by the 1st shift assistant operator every day. 11. Take suitable steps to avoid overloading of equipments and feeders. 12. Maintain the system voltage within the statutory limits with appropriate tab selections as far as possible. 13. Checking of battery conditions and battery circuits. 14. Ensure that the compressed air system and SF6 gas system are in healthy condition and air tank pressure and pressure of SF6 system within are limits. 15. Carry out various routine operations symmetrically as scheduled below separately. OPERATIONS TO BE CARRIED OUT  FAULTS ON TRANSFORMERS If the circuit breaker of a transformer has tripped, the alarms may be accepted, the relay indications carefully checked and noted. If the tripping is an Overload, switch off all the outgoing feeders from the transformers. Reset the relays and test charge the transformer on no load. 50

Then charge the outgoing` feeders one by one and ensure that the load is not more than the capacity of the transformer. If the tripping is for any other reason other than the over current, the transformer may be charge only after consulting the higher officials.  INCOMING FEEDERS If the incoming feeders are tripped on over current relay, reduce the load on the transformer by switching off outgoing feeders from the transformer. Reset the relay and charge the incoming feeder. Then charge the incoming feeder one by one. If the incomer is again tripped, the outgoing feeder last charged may be kept open and other feeders charged suspecting fault on the particular feeder. The load on the transformer may closely be watched and if found exceeding the admissible limit, the distribution authorities may be directed to limit the current.  OUTGOING FEEDERS EXCEPT AUXILIARY In case an outgoing feeder is tripped, accept the alarm, note the relay indication, reset the relay and accept the alarm and test charge the feeder. If the feeder trips instantly or any apparent fault or heavy fluctuations in the supply system, flashing the cubicle are noted, the feeder may be declared as faulty after confirming that the fault exists on the feeder beyond the outdoor isolation point by isolating the AB switch and charging the cable portion from the control room. Inform the distribution section to rectify the fault. If a feeder trips on OC relay, only three test charging may be attempted. Avoid further test charging until confirmation from distribution authority is received that the load on the feeder has been reduced.  AUXILIARY FEEDER The method in the case of other outgoing feeder may be adopted in this case also. But as the station supply is taken from the beach feeder, when the feeder is faulty, open the AB switch in the 11kVoutdoor structure and charge the breaker for taking the auxiliary supply, inform the matter to distribution section. 51

SPECIFIC OPERATING INSTRUCTIONS-PANELWISE A. 110kV feeder panel 1. Distance protection relay i. Note that operated zones and phases by pressing the read button(THR relay) ii. Reset the relay by pressing read and reset buttons simultaneously. iii. Also reset the auto reclose relay if locked out. iv. Reset the master trip relay. 2. Gas pressure low i. Inform the station engineer. 3. O/C and E/F protection relay i. Note down the indication and reset the relay. 4. VT fuse fail alarm i. Check the soundness of the VT fuses in the relay panel and in the terminal box of PT in the respective feeder. ii. Replace the blown out fuse. 5. Auto reclose operated i. Note the dist. Relay indications ii. Reset the relay 6. Auto reclose lock out This indication will always be coming with distance protection trip. Those instructions given for dist. Relay trip is also holding good for this. B. 110kV panels 52

1. IDMT Relay- note fault indications, whether phase fault or E/F or both and test charge as per instruction. If fault persists declare the line faulty and inform the concerned Ele. Section Office. C. Transformer panels 1. OLTC Panels i.

ii. iii.

iv. v.

Oil/ winding temperature alarm - check whether the alarm is due to cooling fan failure. If so inform the concerned engineer. Also check the valves of radiators are open, LT supply to fan intact etc. Oil/winding temperature trip - check whether the tripping is due to over loading of the transformer. then acts as higher official’s direction. OLTC out of step - please put OLTC OPERATION SELECTOR in the independent position for all the three transformers and check whether remote independent operation is possible. If not, go to the transformer yard and local electrical operation may be tired, if failed do mechanical tap changing by handle operation. And put all the three transformer on the same tap position. If local electrical tap changing is also not possible, check LT supply fuses to OLTC motor. for all other conditions inform concerned engineer. Low oil level alarm - visually inspect oil level in the conservator and inform to concerned engineer and acts as per his direction. Cooling fan trips - check for LT supply to the motor, if a fuse are blown out, replaces them and reset.

2. Transformer panels

53

i. ii. iii. iv.

Diff. relay, transformer main tank and OLTC buchholz relay and REF trip - accepts the alarm and inform concerned engineer and acts as per their directions. Transformer oil/winding temp. alarm - inspect the cooler valve, cooler fan, LT supply to fan motors. If fan is not working, inform concerned engineer. Transformer OLTC alarm - identify the alarm indication in OLTC panel and inform concerned engineer and acts as per his direction. Transformer fault trip – identify the trip indication in the window annunciator in the OLTC panel. Then inform concerned engineer and acts as per his direction.

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110 KV PUDUKKAD SUB STATION

INTRODUCTION The 110kV substation Pudukkad is situated at Thoravu& Amballur villages. . At present 110KV substation, Pudukkad has two 110KV feeders, normally 1IRJK and 1MADKT feeders. The substation is normally fed from 400KV substation Madakkathara directly which is entering 1st bay in the yard. There is also an alternate feeding from 55

Madakkathara through Irinjalakuda which is entering 2nd bay in the yard. Both feeders may be tied at this substation, according to the power demand at the both ends. The 110KV substation, Pudukkad is equipped with 2 nos. of 12.5MVA 110/11KV TELK made transformers. Substation supplies seven 11KV feeders including station auxiliary.The11KV feeders feeds to the nearby places such as Alagappa, Cheruval, Kallur, Chengaloor, Amballur, and Palapily. Its station capacity is 25 MVA. The substation is extended in 4.665 Acrs. This substation is commissioned on 22/05/2015.

LAYOUT OF THE SUBSTATION

56

57

NAME PLATE DETAILS OF EQUIPMENTS TRANSFORMER NO.1 WITH ON LOAD TAP CHANGER No load voltage

HV 110000 kV LV 11000 kV

Impedance voltage 10.04% Rating

12.5MVA

Type of cooling

ONAN/ONAF

Current

HV

52.5A / 65.7A

LV

525A / 657A

No. of phases

3

Frequency

50 Hz

Mass of core & winding

13100 Kg

Mass of oil

6960 Kg

Total mass

29060 Kg

Volume of oil

7820 L

Untanking mass

13100 Kg

Air circulation m^3/ min

6*90

Diagram of connection no.

3RD-2171la 58

Guaranteed maximum temperature rise of oil 45°C, winding 55°C Winding HV line HV neutral LV line HV neutral

Impulse test Voltage kv peak 550 95 75 75

AC withstand test Voltage kV rms 230 38 28 28

HV ON LOAD TAP CHANGER Tap selector connection Position Connections u v w HV line terminals Tap selector Voltage current 1 13 112750 64.1 2 12 111375 64.9 3 11 110000 65.7 4 10 108625 66.5 5 9 107250 67.4 6 8 105875 68.2 7 7 104500 69.1 8 6 103125 70.1 9 5 101750 71.0 10 4 100375 72.0 11 3 99000 73.0 TRANSFORMER DRIVING MECHANISM TRANSFORMERS AND ELECTRICAL KERALA LIMITED MADE IN INDIA Type

D2

Control circuit voltage

1 phase 50Hz 110V

Time for one operation

5sec 59

No. of working taps

11

REF STD IEO 214 05HP 3 phase 415V 50Hz 1 Phase 415V/110V 500VA TRANSFORMER NO.2 Transformer specification REF I.S

2026-1977

Basic insulation level Impulse voltage HV

550kvp

HVN

95kvp

LV & LVN

75kvp

P F Voltage HV

230kvrms

HVN

38kvrms

LV & LVN

28kvrms

Type of cooling

ONAN /

Rating in KVA

10000

ONAF

/

12500

No load voltage HV

110000V

LV

11000V

No. of phases

3 60

Impedance voltage

9.9%

Frequency

50

Hz

Core and winding weight

11800kg

Weight of oil

87825kg

Oil quantity

9870ltrs

Total weight

31085kg

Transport weight

23000kg

Guaranteed maximum temperature rise for oil / winding 50°C Year of manufacture Diagram of connection no.

OLTC POSITION 1 2 3 4 5 6 7 8 9 10 11

2007 3RD-21617la

TAPPINGS CONNECTED 13 12 11 10 9 8 7 6 5 4 3

HV VOLTS 112750 111375 110000 108625 107250 105875 104500 103125 101750 100375 99000

STATION AUXILARY TRANSFORMER 61

LV VOLTS

11000V

Capacity

160KVA

Voltage ratio

11000/433V

Current ratio

8.39/213.33A

Make

KEL

Type of cooling

ONAN

% impedance

4.32%

Total weight

829kg

Core & winding weight

209kg

Frequency

50Hz

No. of phases

3

Oil in litres

235 l

Max. Temperature rise in oil

45°C

110kV SF6 CIRCUIT BREAKER OF TRANSFORMER NO.1 Rated voltage

123 kV

Normal current

1250A

Frequency

50 Hz

Impulse level

550 kVp

Rated short circuiting braking current 25 KA Rated making capacity

50 KA 62

Rate duration of short circuit current Total braking time