Alstom Training Manual

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Introduction

o &tie" cwetYiew 01 substation engineering

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ubstations form on important port of the transmission and distribution networks of electric p;;,wer system. They control the supply of power on different circuits by means of various equipment such 0$ transformers, compensating equipment, circuit breakers, etc. Various circuits are joined together through these components to bus bar systems at the substations. While the bus-bar systems follow certain definite patterns, limiting the scaP'! for variation, there is practically no standardization regarding the physical arrangement, called the layout of the various components relating to one another. For the some type of bus-bar system different layouts have been used in different countries and in fact in Indio there are variations in this regard not only among the various State Electricity Boards but also within a State Electricity Board. This manual gives the basic requirements ond for the sake of illustration contains typical layouts for various types of bus-bar systems.

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One of the primary requirements of a good substation layout is that it should be as economical as possible, but it should ensure the desired degree of flexibility and

reliability, ease of operation and maintenance, expansion and meets all safety requirements of the operation and maintenance personnel. Besides, the layout" should not lead to breakdowns in power supply due to faults within the substation, os such faults are more serious. A brief discussion on the various components and auxiliary facilities required in substation and how they affect the layout is included.

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Many standards viz. IS, as, lEe, IEEE and the like guide the design of substations. It is essential that the equipment used and the practices followed conform to the latest standards, as required by the customer.

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This manual is aimed at understanding the basis of sub-station design. If deals with voltage levels between 33 kV and 400 kV and standard switching schemes. It also discusses, briefly about sele"~'on of major equipment.

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Substation types

introduces lhe di(fll!rent types 01 sub·sla/ions

Generation station

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Generation is done at 11 kV - 15 kV level. As power of very high capacities cannot be .,;::nsmitted for long distances at these voltages it is stepped up using generator transformers to 110 kV - 400 kV levels. Generation stations are. in simple terms, step-up stations.

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Grid station

(.)

Grid Stations are used to interconnect different grids/regions/sectors. They are generally 400 kV substations. They are stotions, switching power from one generation/grid station to other. They can olso be called Switching Stations.

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Distribution station Distribution Stations are located at the load points where the power is stepped down to • 11 kV - 110 kV levels.

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Bulk Industrial supply stations

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Bulk Industrial Supply Stations are distribution stations catering to one or 0 few consumers. The supply voltage can range from 33 kV to 110 kV. Industriol users do have their own generotion focilities besides the. SEB supply and these s1a1ions oct as step-up stations as well.

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Sur' stc POSHI\;,;n

can also be classified as Step-up stotions, Primary grid Stations, Secondary Sub-secondary stations and Distributions stations depending upon their in the power system hierarchy. :1S

Generally the Substations are of outdoor type for 33 kV and above. EHV Stations can be indoor depending upon the environmental conditions like, pollution, salinity etc., and space constraints. Indoor stations are Air - Insulated or SF6 gas - insulated depending' upon the availability of space and financial constraints. Gas Insulated Substations (GIS) are extremely costly and requires extra maintenance and hence are preferred only when it is absolutely necessary.

Salient features of major equipment

Major eqc.. ,Omenl In a $vbslalion.

T

r.... substation layout is influenced to a great

r .,

·~xtent

by the dimension of the

eCjUlpment and their accessories within the substwlon.

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Circuit Breakers

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Circuit Breaker is a mechanical device capable of making, carrying and breaking

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currents undN normal circuit conditions and making, carrying for a specified time and breaking j

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under short circuit conditions. Circuit Breakers of the types indicated

below are used in India.

G

36 kV

Minimum oil/ Vacuum / Sulfur hexa fluoride (SF6)

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72.5 kV

Minimum oil/ Sulphur hexa fluoride (SF 6)'

145 kV and above

Sulphur hexa fluoride (SF,,).

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245 kV and higher voltage outdoor circuit breakers, generally necessitate the

provision of approach roods for breaker maintenance.

400 kV CBs may hove pre-insertion resistors depending up on the system

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requirement. When a CB interrupts a transformer or a reactor circuit, switching over

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voltages can be' more than 1.5 p.u. or 2.5 p.u. respectively (maximum limit

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recommended by IEC). resistors are required to prevent restrikes due to current chopping. When lightly loaded tines are disconnected, interruption of capacitive

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currents take place causing restrikes which can set in oscillations of a few hundred Hz.

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CBs with self. generating pressure and comparatively slow contad movement, such as.,

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bulk·oil, minimum- oil, SF" puffer type might restrike. However, modern SF 6 puffer type breakers are designed, restrike-free.

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CBs can be live tank type or dead tonk type depending up on ihe substation design and economy. Dead tank type CBs come by design with sets of current tronsformers on the bushings. They are normally used in the l'h breaker or Ring bus scheme, where, there are CTs on either side of the CB. This type of compared with a live tonk type

ca and

ca is less expensive when

two free standing (generally oil filled) CTs

combination. These are not popular in Indio. ~

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Live tank CBs are used in other schemes where CTs are not required on either sides of the

ca, like double main scheme, double main transfer scheme etc. as they ore less

PlCnensive than dead tank CBs.

Disconnect Switches and Earth Switches

Disconnect switches are mechanical devices which provide in their ope.. ' positions, isolating distances to meet the specified dearances. A disconnect switch can open and dose a circuit when either a negligible current has to be broken or mode or when

....

·';"ere is no significant change in voltage across the terminals of each pole of the

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Qlsconnect. It can also carry currents under normal circuit

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!itions and the short

circuit currents for a specified time. Disconnect switches are used for transfer of load from one bus to another cnd to i$«

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equipment for maintenonce.

Although a

variety of disconnect switches are available, the fadar which hos the maximum

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influence on the station layout is whether the disconnect switch is of the verticol breok

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type or horizontal break type. Horizontal break type normally occupies more space \

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than the vertical break type.

Between the horizontal center break and horizontal

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double break types, the former requires large phase to phose clearance.

The location of disconnect switches in substations affects not only the substa,ian­ loyouts but maintenance of the disconnect contacts also.

In some substations, the

disconnects are mounted of high positions either vertically or horizontally. Although such substations occupy lesser area, the maintenance of those disconnect switches is more difficult and time consuming.

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The disconnect switch serves as adamonaf protection for personnel, with breoker 11\

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or!'ln, during maintenance or repair work on the feeder and also enobles the breaker ;... ,,;e isolated from the bus for inspection and maintenance.

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Earth

~itch

is a mechanical switching device for earthing different ports of a circuit,

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which is capable of withstanding short-circuit currents, for a specified time but not

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required to carry normal rated currents of the circuit.

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Instrument Transformers

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Instrument transformers are devices used to transform currents and voltages in the primary system to values suitable for ins1ruments, meters, protective relays etc. They isolo:e the primary system from the secondary.

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Current Transformers (CTs) may either be of the bushing type or wound type. The bushing type is accommodated within the transformer bushings and the wound types

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are seporateJy mounted. The location of the

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breaker depends on the protection scheme and the layout ofsubstotion as. well. So

cr with

resped to associated circuit

for. Ihe wcund type CTs with dead tonk construction has been useo. Howeve,. current transformers with live tonk construction also are being offered. It is ck:lImed thot These transform"":; offer the following advantages:

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capable of withstanding high short circuit currents, due to their short and

ngid: mary conductar and hence more reliable, • They r.:Jve

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reactance and therefare hove better transient performance.

These current transfarm€;: s do nat have their majar insulation over the high currer' carrying primary. Therefore, the heat generated is easily dissipoted due to which "1e insulation has superior thermal stability and longer life. However, these have "mitations in withstanding seismic forces and have

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handled and

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transported carefully, ,.".. -,' .~

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Different classes of accuracy

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The two different uses of a CT are

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• Protection

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Metering

These two requires conflicting properties of saturation, hence different types of cores are used. For protection, the CT should faithfully reproduce the changes in the current for higher magnitudes, whereas for metering, the CT should saturate at higher magnitudes in order to prevent any damage to the meters.

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Protection Classes· (110.

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PS

Closs PS CTs are

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low reactance and their performance will be spec"

. In

terms of the following charaderis:;cs. 1. Turns Ratio, which will be numerically the same as the roled

transformation ratio. 2. Minimum Knee-Point Voltage (Vk), specified in accordance with the formula; Vk K

= K I, ( R.:, + RJ

-+ poromete~ specified by the purchaser, which depends on the system foult level

and the characteristics of the refoy, intended 10 be used

-+ rated secondary current of Ihe CT R.:, -+ resistance of the secondary corrected 1o 7O'"C ~ -+ impedance of the secondary circuit as pacified by the purchaser

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3. Maximum Exciting Current, at the rated knee-point voltage or at any specified fraction of the rated knee-point voltage.

In this way, a CT designated in terms of percent composIte error ond accuracy limit factor

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Composite errDI'". Ihe RMS value of Ihe difference oetweefl til" ,nSlontancous

volues

at

Ihe prtmory current and lhe rated Iranstormohon

secondary currenl. The standord composile errors '"

P -+ Y

rohO hOles the

~rcent

oct"ur

are 5. 10 and 15

Protection

-+ Accuracy limit factor, Ihe ralio of the raled accuracy 1.01.1 pnmary :urreonllo

lhe rated primClrf current, where raled occ:vracy Iim.1 primary current

IS

th. value of

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lhe highest primory currenl up la which the transformer will comply w.th the specified

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limits of the compqsile error. The standard accuracy hmit foclors are 5. 1O. 15. 20

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Voltage Transformer (VTs) may be either Electro-magnetic type (IVT) or capacitor

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type

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(CVT). IVTs are commonly used where high accuracy is required, like revenue

metering. For other applications CIT is preferred particularly at high voltages due to

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their lower cost and can be used as a coupling capacitor, as well. for the Power line

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Carrier Communication (PlCq equipment. Each CVT will be earthed through an

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earth electrode.

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For ground fault relaying, on additional core is required in the VTs, which can oe

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connected in open delta. The VTs are connected on the feeder side of the circuit

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breaker and on the bus bars for synchronization.

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The standard accuracy classes for ClTs will be

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for m~csurement, 0.2, 0.5, 1.0 and 3.0

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for protection, 3P and 6P

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.ormer

Transformer is the largest piece of equipment in a substation ond it is, therefore,

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dimensions and reliability, it is generally not possible to accommodate two

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wider than the bay width.. In order to reduce the risk of fire, large transformers are

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provided with stone metol filled sooking pits with voids of capacity adequote to contain

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important from the point of view of station layout.

For instance, due to its large

transformers in adjacent boys. One of the problems could oe, the radiators being

the total quantity of oil. Besides, separation walls are provided in-between the

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transformers and between transformers and roads within the substation.

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One of the important factors governing the layout of the substation is whether the V

transformer is a three-phose unit or a bank of three single-phose transformers. The ~.

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space required for single-phase banks is more than that with three-phase transformers. Besides, single-phose bonks are usually provided with one spare single­ phose transformer, which is kept in the service boy and used in case of a fault or

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01 one d the single-phose

o~rmonen!iy

installed in the switchyord ready to replace the uni:,

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Allernatively, the spore

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be of

::;",'Vlce. Tni:;, however, requires on elaborate bus arrangement and isolalor SWitching.

Reactivi' Compensation Equipment Reactive compensation may be switched or non-switched type as indicated by system studies

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Ine network. The non-switched type compensation usually comprises shunt

reactors p-:::rmonently connected to transmission line or to bus bars at the substation. t-.lext to Ih· transformer, shunt reodor is the largest piece of equipment. These also

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can be

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In

the form of single-phase units or three· phose units.

Often, neulral

grounding reador, which is connected between the neutral bushing of the line shunt reactor ....

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the earth is provided to facilitate single·pole auto reclosing. Since these :00

contain oil, all fire-safety precautions that are token for transformers

should be followed.

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Switched compensotion can be through switched reodors, switched capacitors or· thyristor controlled readors and thyristor switched capacitors known as Stotic VAr Compensators (SVC). These are selected according to the system requirements and conneded diredly to the system through their own dedicoted tronsformers. The shunt capacitor bonks ore composed of 200·400 kVAr copocitor units mounted on rocks in series/parallel operated in.groups to provide the required reodive power (MVAr) output at the system voltage. Mony.o.time only some of trese moy be required in the initial stage and may undergo alteration as the system develops.

Dired Stroke Lightning Protection

Any substation hos to be shielded from direct lightning strokes either by provision of overhead shield wire/earth wire or spikes (masts).

The methodology followed for

systems up to 145 kV is by suitable placement of earth wires/masts to provide coverage to the entire station equipment. Generally, 60° angle of shield for zones covered by 2 or more wires/masts and 45° for single wire/most is considered adequate. For installations of 245 kVand above, eledromognetic methods are used. The commonly used methods for determining shielded zones are the Mousa Method and Razevig Method.

Surge Arrestors/Lightning Arrestors

Besides direct strokes, the substation equipment has also to be protected against travelling waves due to surge strokes on the lines entering the substation. equiprlent most commonly used for this purpose is the surge arrestor

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The

the line entry

of the __ ostalion. The most important and the costliest equipment in a sub_ .1110n is the trans: - -ner and the normal practice is to install surge arrestors as near the ,

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transL cner as possible. :~;bstal;on

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The fixing up of insulation level for equipment within a

requires a detailed insulation co-ordination s1udy with surge arrestor as the for protecting the equipment from power frequen-:

,-/er-voltoge exceeding

the or- estor rating. Besides protecting the transformers, the surge arrestors also

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protee to the equipment located W"',in their protection zone

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arresters con be provided, depending up on, the isocerounic level, anticipoted

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Additional surge

overvohoges and the protection requirements.

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Insulators

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Adequate insulation should be provided in a substation for reliability of supply ond However, the station design should be so evolved that the_

safety of personnel.

quantity of insulators required is the minimum and commensurate with the expected security of supply.

An importont consideration in determining the insulation in a

substotion, porticularly if it is located near sea, a thermol power generating station or on industrial place, is the level of pollution, which can be combated using insulators of higher creepage distance. In case this does not suffice, the insulators need to be hot line washed periodically and this aspect has to be kept ,in mind while deciding the loyout of the substation. -.:,..~iying suitable type

Another method, which hos proved to be successful, is

of greases or compounds on 1he surface of the insulators ofter

cleaning, the frequency depending upon ~ degree and the type of pollution.

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FOLLUTION LEVELS AND MINIMUM NOMINAL CREEPAGE DISTANCE TO BE

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ADOPTED AS PER IS/IEC

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Pollution Level

Min. Norrinal Creepage Distance (mm/kV)

Type of Pollution

Light

16

Non-Industrial, Agricultural, Mountainous areas beyond 20 Km from sea

Medium

20

Industrial Area without polluting smoke and chemical effl uents and not too dose to sea

Heavy

25

Industrial Area with polluting smoke & chemical efffuents close to sea and exposed to strong winds from sea

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Very Heavy

31

The highest line-to-Iine voltage of the system .'

Industrial Area subjected to conductive dust polluhon, smoke very close to sea, exposed to sea and very strong winds from sea, desert areas etc. IS

used to determine the creepage

distance

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The following types of insulators are normally used: a)

Bus Support Insulators (i)

b) 'c, _

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(3 .~

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Solid core type

Strain Insulators (i)

Disc insulators

(ii)

long Rod Porcelain insulators

(iii)

Polymer insulators

Structures The cost of structures also is a major consideration while deciding the layout of a' substation.

For instance, in the case of flexible bus-bar arrangement, cost of

structures is much higher than in the case of rigid bus type. Similarly, the form of structures also ploys on important port and the choice is usually between using a few heOYy structures or more number of smaller structures.

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Hot-dip galvonized steel is the most commonly used material in Indio for substation structures. When, galvanizing is not effective; particularly in a substation located In coastal or industrial areas, paInting becomes essential.

Q Power Line Carrier Communication (PLCC)

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The carner equipment required for communication, relaying and tele metering is

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connected to line through high frequency coble, coupling capacitor and wove trap.

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The wave trap is installed at the line entrance. The coupling capacitors are installed on the line side of the wave trap and are normally base mounted. The wave traps for voltage levels up to 145 kV can be mounted on the gantry structure on which the line is terminated at the substation or mounted on top of the capacitor voltage

-

transformer. Wave traps for voltage level:.; of 245 kV and above generally require separate supporting insulator stock mounted on structures of appropriate height, however, 245 kV wave traps can also be suspended from the line side gantry.

The differ-ent types of coupling used are •

Inter-circuit coupling

Incase of double circuit lines one phose on each circuit need be used lor communicotion. This type of coupling is called inter-circuit coupling. •

pr.~:e

to Phose coupling

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of single circuit lines coupling con between any two pi-::Jses of

tne circuit depending up on the impedance of the phases • Phose to Earth coupling Any one phose only can be use~ for carrier communication where the

earth is used as the return path.

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'C'OUPLING 1 [50

=

(1000 + 1.5C, P.)O. 116/" t,

E sfap50

=

{1000 + 1.5C, p,}0.1571" t,

=

1; for no protedive surface layer

Where,

C.

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1

=

0.96

[

a 1+2 L

-:-:=:=K="::;::::;;:::--J' ; otherwise

n_1

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1+(2nhjO.08f

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Simple c: 'ernative approaches, based on the equivalent hemisphere, such as

= f

1-0 [l-P/P. I 2h,+a)

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approximately; a= 0.106 m. which avoids infinite summation series, olso possible

the resistivity of the surface material in Om t. = duration of shock cu' 'ent in seconds The actual touch voltage, mesh valtagt:, or transferred voltage should be less than the =

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maximum allowable touch voltage, Eloudv to ensure safety. However, ElINp50 &

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are taken into consideration, os these would give lesser

limiting volues.

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Grounding System Elements

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1. Ground electrode: A condudor imbedded in the earth and used for collecting ground current from or dissipating ground current into the earth.

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2. Grounding grid:

A system of horizontal ground electrodes that consists of a

number of interconnected, bare condudors buried in the earth, providing a common ground for eledric;al devices or metallic structures, usually in one specific location. NOTE:

Grids buried horizontally near the earth's surfac. or. alS? effective in controlling the svrfoce

potential gradients. A typical grid usually is supplemented by a number of ground rods and may be f, ., 'p and

(v)

Calculate Em and E" L.:,

(vi)

Check Em< E..,...;., Es< E.,ep, L.:>l,.q & Rs < R,eq.

(vii)

If yes increase the spacing and check until the conditions foil.

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substation are diredly dependent on the soil resistivity

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Rc

(viii)' If no decrease the spacing and check until the conditions are passed.

Calculation of Maximum Step and Mesh Voltage:

Em

=

pK",KHl and

E,

=

pK.,KHl

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Mesh Voltage (E...):

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spcclng fador Em for mesh voltage by simplified method is:

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[t In

:::;

2j[

::J K

~:'}

1,.

=

with ground rods ~nroughout

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K

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•

• 0

...

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f'l

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16hd

BOd

h

J

--

+

4d

8'

K..

p(2n.l)

10

the grid corne .~. as well as both along the perimeter and

the grid area•

=

for grids with no ground rods or grids with only a few ground rods,' none located in the corners or on the perimeter .

+ h/ho

K_

=

..)1

h..

=

1 m (reference depth of grid)

D

=:

spacing between parallel conductors in m

h

=

depth of ground grid condutors in m

n

=

number of parallel condudors in one direction

d

=

diameter of the grid condudor in m

Corrective Factor:

0.656 + 0.172 n

K

For mesh voltage calculation,

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n

=

~

Where x & yare condudors in each diredion.

For easy identification, K; for mesh voltage calculation is denoted as K!!l'

For step voltage calculation,

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n

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For easy identification, K; for step voltage calculation is denoted as K;!.

=

max(x,y)

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K,.

-In­

for grids with ground rods along the perimeter, or for grids

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(O+2h)'1

·· ..ere

s}

0

°'1

-+

Step Voltage (EJ:

The spacing foetor ~ for step voltage by simplified method is

K

=

1

-

1

1

1

'I

+ - + -O-O:Sfto').,

i

2h

o

D+h

Moreover, for depths smaller than 0.25 m.

K.,

=

1 [

1

1

:----;

+ -

D+h

+ 0

w]

Where

w

"..,

+ 2

4

n-1

Or for n ~ 6

.:t

­

W

,..j.

= - -

+ In (n-1) - 0.423

2(n-1)

.....,

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+

+

3

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The use of a different equotion for 1(., depending on the grid depth h, reflects the fad that the step voltage decreases rapidly with increased depth.

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In equotion for Em ond E,

L

4J 0

• • •• ,

0

)

=

L.+L,

for grids with no ground rods or only a few rods in e the center oway from the perimeter

=

1..+

for grids with ground rods predominantly around the perimeter.

1.15L,

Estimation of Minimum Buried Condudor Length .

K", K P IG ,,~

.

L >

116

+ 0.174 C, P

Refinement of Preliminary Design: If colculations based on the preliminary design indicate that dangerous potential

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differences can exis1 within the station, the following possible remedies should be

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studied and applied where appropriate.

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{1)

Decrease in total grid resistance will decrease the maximum ground grid

;,

" potential rise and hence the maximum transferred potential. The most effective way to

"...

decrease ground grid resistance is by increasing the area occupied by the grid. Deep driven rods or wells may be used if the ovailable area is lirnited. Decrease in

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stotion resistance mayor may not decrease appreciably the local gradients, depending on the method used .

(2)

Improvement of Gradient Control.

By employing closer spacing of

grid condudors. the condition of the continuous plote can be appraached more eiosely. D::'~gerous

potentiols within the station can thus the eliminated at a cosl. The

problem c" ''"Ie perimeter may be more difficult, especially at a smal! station where earth res::' ,ity is high.

-However, it is usually possible, by burying the grid

perimeter ground condudor outside the fence line, to ensure that the steeper gradients

l~'mediatety

outside this grid perimeter do no1 contribute to the more

dangerous ::::>uch contacts. Another effedive and economical wav to control perimeter ...,.,

gradients cnd step potentials is to bury two or more parallel conductors around the perimeter at successively greater depth as distance from the slalion is increased.

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(3)

Diverting a greater part of the fault current to other paths. For

example, conneding overhead ground wires of transmission lines or by increasing the tower footing resistance near the substation.

Concerning the lotter, however. the

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effed on fault gradients near tower footings should be weighed.

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(4)

Limiting of short-circuit currents flowing in the ground mat to

lower values. If feasible, this will decrease the total rise in ground mot voltage and

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all gradients in proportion. Other fadors, however, will usually moke this impractical.

0

Moreover, if accomplished at the expense of greater fault clearing time, the danger

a

may be increased rather than diminished.

n

•

~

I'

Barring of access to limited areas where it'may be impractical to

e:ote possibility of excessive potential differences during a fault.

By uSing one or more of the above methods where necessary, designs can be

~

completed for construdion purposes.

D

grounding facilities can usually be installed more cheaply if all go in as port of the

-"

general construction job, without the necessity of making addITions later.

...i

)

These should be reasonably liberal, as

Limitations of Simplified Equations for Em and E.:

"")

....:

..

Severol simplifying assumptions are mode in deriving the equations for Em and Es. These assumptions may result in inaccurate results, for some cases, in comparison with the results from more rigorous computer analysis or scale model tests.

The

inclusion of correction fadors into the equations for Em and E, practically eliminates the inaccuracy (within certain ranges for the various parameters) for most pradical grid designs.

)

\}

0 3

When using the equatlons for E.., and E•• the following limits are recommended for

")

square grids, or for rectangular grids having the some number of condudors in both diredions:

'-, ....__ 0'

n

0

S

25

0.25 m

~

h

-:;

d < 0.25 h

1)

D > 2.5m

2.5m

Although the equations for Em and E. have been tested for n greater than 25 and

0

found to be sufficiently accurate, the tests were not extensive enough to form solid

o.

conclusions.

Thus, caution should be exercised before exceeding the limits given

above.

0 ~

~

;tance:

Grid

) 1

G

e 0 tl)

Where,

• 0

h

=

grid buried depth in m

A

=

Area of grid in m'

L

=

totollength of condudor in m

0

• ~

Calculation of Maximum Step and Mesh Voltage:" Based On IS 3043 Area of Cross Section )

The areo of cross section required for the ground condudor is,

3

•

l...n

s

k

0

Where,

0

S

0 :J ...., ~

=

k

=

Cross section areo in mm'

=

rms value of fault current in A

=

duration of fault in s

=

fador dependent on material of the protective conductor

The factor k is

{) Q., (8 + 20)

~ ~.

K

=

~

~

+

B

.:-}

')

9;

\"'i~=re,

:>

Bus Post Insulators.

CJ '#,

U

Disc Insulators.

)

3.

')

• • • •e· •

4.

~

i

.~

.

ft-

)

Boy Morshalling Kiosks.

5.

Cf/VT/CVT Junction Box.

6.

Clamps & Connectors for equipments and busbars.

7.

Busbar materials.

8.

a) 1.1 kV Power & Control Cables and Cable Glands. b) H.T. Power Cables and Jointing Kit.

9.

Coble Trays & Support Angles.

10.

Sattery & Bc:ttery Chargers.

11.

AC Dish

12.

.. 6c Distribution Boord. a} Earthing Materials. b) lightning Protection System.

14.

Illumination for Switchyord & Control room.

15.

Fire Fighting System (portable/spray hydrant system)

16.

Structures.

17.

Neutral Grounding Resistors.

0

18.

Diesel Generating Sets.

I;)

19.

SCADA.

Z,

20.

Toriff metering system.

~

21.

Auxiliary Transformers.

22.

Air Conditioning & Ventilation.

iJ

0

) i

#

13.

• "

i

Insulator Hardwares with Sag compensation spring (if required).

!)

j

Major technical parameters considered for equipment are:

0)

Rated voltage.

b)

Design ambient temperature with permissible maximi.:m temp. rise.

c)

Breakdown insulation level.

d)

Creepage distance.

e)

Rated current carrying capacity. Rated short circuit current capacity with duration. Materiological data like altitude, wind speed, maximum & minimum temperature, se;

I)~::".". Electro mechanical strength of string insulators.

.3t..

It

'

Cantilever stren:;)

.

.,"­

---~-- 6J-' --JiOximum sag for longest proposed span. \

lot

7)

Main busbar height from ground (finished level}.

.Following parameters are to be obtained from customer in the absence of detailed specification and drawings for rough estimation:

l.

Soil data with soil bearing capacity and soil resistivity.

2.

Plot plan of the proposed area.

3.

location of the Control Room with resped to Switchyard.

4.

Distance of the Switchyard fence from the Power House, in case of Power Station.

5.

location of the Generating Transformer with respect to Switchyard.

6.

length of the Transmission lines connected to the Switchyard.

7.

Available space for Switchyord (fence area}.

.J

8: -.. Additional provision for spore bays.

Follo~!_ng

information are to be obtained for availability of adeguate site faciliti€...:.

1.

location of proposed site and nearest railway station.

'J

2.

Acces$ibility to site by rood.

~

3.

Construction & drinking water (free/chargeable).

4.

Construction power (free/chargeable).

:') -~-

()

-:...=;:;:

o

Following information are to be obtained for pl0viding post commissioning services to customer.­

J. Requirement of mandatory spores.

o ) d

€I.

2. Requirement of recommended spores. ... ;.

G

4

:--,.=~:·'j~'-:R~Uii~ment of special tools and tackles for operation & maintenance. ~~~:'~1.~~~'~~.&:

~~:.",=. ~~'R~uirement of testing equipments.

.

_~

•

1.)

Following datos are required generally from customers for reasonable quotation:

9 •.

~_~1:':~:t'~~);"~: Breaker -

-,...;-'

'\1)

.,. o

: Single pole/gang operated, live/dead tonk, pneumatic/spring operated type, duty cycle requirement, creepage for interrupter (arc chamber), as well as support insulator, closing and opening time, 'indudive/capacitive charging curr~nt rating. live/dead tonk type, nominal capacitance in case of cvr, Transformers creepage of the bushing • Shed profile, creepage, cantilever strength.

d)Disc Insulators

Disc insulators string/long rod insulator, electro mechanical strength.

e)C&R Panels

1) Numerical/static/eledro-magnetic relay. 2) Additional requirement of Tariff metering with closs of accuracy. 3) Requirement of busbar protection. 4) Requirement of synchronising panel/trolley. S} Requirement of separate disturbance recorder with event logging. 6) 'Requirement of recorders like voltage, frequency etc. 7) Requirement of interfacing with SCADA.

8} Requirement of mimic panel. 9) Simplex/duplex type of panel.

f) Isolators

Single/double break, Conventional/Pantograph, single pole/gong operated, motor/manual operated, aluminium/copper blades, creepage and cantilever strength of suaport insulators.

g) Cables

PVC/XlPE, Copper/Aluminium, Flame retardant/ordinary

h}Busbar

Flexible/ Rigid bus, Copper/Aluminium material

i)Earthing material

MS, GI/Copper bars

j) Battery

lead acid/NICAD, ordinary/maintenance free acid.

-.

()

.

-,

Armoured/U narmoured,

'-'"

? 0 ....,1

k) PLCC

~:)

~

i)

lightning Protection

il

Illumination

0

i.:)

""

i} Phase to phase/Phase to Earth/Phase to Phose inter circuit coupling (in case of double circuit line).

iii} Milli Henry requirement of line trap .

• ,

t

k)

Structures

)

'~

By lightning Mast/Shield Wire/Spikes on the Gantry Towers. Using lightning Mast/separate lighting Most or poles for light fixtures .

1} Conductor tension for line take off/line termir

gantries.

2} Short circuit forces.

v

.

'J

4} Gantry arrangement.

~)

5) Conductor span.

3) Wind pressure .

-..,.

6} Minimum & maximum temperature of the proposed areas.

"

,J

,") ... .no,.

Since major equipments with standard rating are supplied by different manufacturers with marginal differer.ce in Ex-works costs, following items need to be near accurately estimated for a competitive quotation in on EHV Switchyard project of turnkey nature,

'\

1}

Post Insulators.

.....

2)

HT & LT Power & Control Cables and Accessories .

.)

J

case of lead

ii) Programmable/non-programmable PlC terminal.

0

•

In

3)

Structures

4)

Busbar materials.

S)

Clamps & Connectors

6)

Earthing material

7)

Illumination System

8)

Post Insulators

....-

9)

Disc insulators & hordware sets

~ ,-L

10)

Lightning protection system

::r·

11)

Battery sizing for totol D.C. loads

~,

....

~

-...L---­

.\

()

,.,.

! 0

'J

0 ~

. •

. 0

-._.

:!)

-

6

)

~

,3

)

il

.

:) -

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j I

.,

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f