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220 KV AIR INSULATED SWITCHGEAR (AIS)

1.0 220 kV CIRCUIT BREAKERS

1.1 DESIGN CRITERIA

a) SYSTEM DATA

1 System voltage 220 KV +/- 10%, 50 Hz +/-5%, 3 Ph.

2 System earthing Solidly earthed3 Highest system voltage 245 KV4 Rated voltage 245KV, 50 Hz, 3 Ph, AC

b) BREAKER DATA

1 Insulation / arc quenchingmedium

SF6 Gas

2 Reference standard IEC 62271, Part 1003 Installation Indoor4 Design ambient temp. 50o C5 Number of Poles 3 single pole / gang operated6 Rated continuous current

at design ambient temp.2000 Amps. 3 Ph. 50 Hz.

7 Rated symmetricalbreaking current

40 kA (RMS) with percentageDC Component as per IEC

8 Rated short-time current

for 3 sec.

40 kA (RMS)

9 Rated peak making current/ Dynamic short circuitwithstand current

100 kA (Peak)

10 Rated line chargingbreaking current

Not < 125A

11 Rated Cable chargingbreaking current

Not < 250A

12 Power frequency withstandvolt. (Wet & dry) betweenphases, between open

contracts, between liveterminals and ground

460 kV (RMS) for 1 Min.

13 Lightning impulsewithstand voltage (1.2 x50 microsecond wave)

1050 kV (Peak)

14 i) Rated operating dutycycle

O - 0.3 sec CO - 3 Min - CO

ii) Dead time of thebreaker to beadjustable between

0.3 sec. to 15 sec.

iii) First pole to clearfactor

1.5

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15 Minimum number of on-offoperations beforemaintenance replacementof any parti) At rated current: Not less than 2000ii) At rated short

Circuit current:Not less than 50

16 Minimum creepagedistance betweenterminals & betweenterminals & earth

Not less than 31 mm / KV ofthe highest system voltage.

17 Number of shunt trip coils 2 Nos. 220 V DC coil forcommon operatingmechanism.

18 Construction of breaker 3 identical single pole unitswith multiple interrupters.

19 Number of closing coils 220V DC (one No.) forcommon operating

mechanism.20 Minimum creepage

distance betweenterminals and betweenterminals and earth

Not less than 7595 mm

21 Operating mechanism Motor wound spring charging /pneumatic / hydraulicmechanism

c) Accessories on breaker pole / operating mechanism cubicle

i) Densimeter with temp. compensated pressure switches withpotential free contacts for fill in alarm / operation lockout.

ii) Filters for absorbing dust, metal vapours and other arcingproducts.

iii) Provision of filling of SF6 gas at site.iv) Operation counterv) Aux. Switch with not less than 10 NO+10 NC contacts inter-

changeable at site per pole of the breaker.

d) Operatingmechanism

Electrical motor operated, springcharging mechanism/ pneumatic /

hydraulic mechanisme) Auxiliary control

voltage220 V DC for motor, closing andtripping coil; 240 V, 50 Hz., single Ph,AC for space heater

f) Components in

the operatingcubicle

As per the write-up given in technicalparticulars

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1.2.0 TECHNICAL SPECIFICATION EHV CIRCUIT BREAKERS

1.2.1 This specification covers extra high voltage SF6 circuit breakers.The design, manufacture, identification, inspection and testing ofcircuit breaker shall comply with the latest edition of standardsand codes specified elsewhere in this specification. In case of

conflict between standards, more rigorous standards shall apply.

1.2.2 SERVICE CONDITION

Circuit breakers shall be suitable for service conditions specified.

1.2.3 RATING

Circuit breakers shall be suitable for operating on voltage,frequency and type of system specified. In general, rated valuesof equipment shall conform to preferred values as listed in

applicable Indian Standards / Indian Electricity Rules.

1.2.4 CONSTRUCTION

GENERAL

The circuit breaker assembly shall be complete with threeindependent poles, operating mechanisms and supportingstructures.

1.2.5 CIRCUIT BREAKER POLE ASSEMBLIES

a. INTERRUPTER UNIT

The interrupter unit shall be designed such that the maximumshort circuit current specified can be safely interrupted within thegiven time limit without causing appreciable damage to the maincontacts.

To minimize burning of the main contacts all parts exposed tothe arc, created by the current interruption, shall be protected bya special arc resistant metal alloy, if necessary.

The circuit breakers shall withstand, without need for inspectionand / or replacement of main contacts and parts located in theextinguishing chamber, the minimum number of operationsspecified.

The number of interrupter units used for the voltage specifiedshall be at the manufacturers discretion.

The SF6 gas used in the interrupter unit shall be adequate gradeto ensure proper operation within the ambient temperature limits

specified.

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The manufacturer shall also specify the nature of inspectionand / or maintenance to be carried out based on elapsed timeand / or operating conditions.

The inspection / maintenance frequency while clearing full ratedshort circuit current shall not be less that 50 and while clearingrated full load rated current, 2000 operations. All the parts

requiring inspection / maintenance shall be easily accessible.

Adequate means shall be provided to ensure Re-strike Freeoperation, especially when interrupting low inductive, orcapacitive currents.

The extinguishing chamber and the contact assembly shall beenclosed in an insulating tube made of porcelain or other suitablearc resisting material.

b. SUPPORTING INSULATORS

The insulators shall be made of high strength porcelain and shallbe suitable for the service voltage and BIL specified.

1.2.6 SUPPORT STRUCTURE (s)

For the circuit breaker pole assemblies, appropriate individual orcommon self-supporting structures shall be supplied according tothe manufacturers standards and / or recommendations.

All support structures shall be made of steel and shall be hot dipgalvanized to a thickness not less than 100 microns.

On each support structure assembly adequate means shall beprovided for the connection of two ground conductors.

1.2.7 OPERATING MECHANISM

Motor wound spring charging / pneumatic / hydraulic type as perdesign criteria.

In case of motor operated mechanisms, closing spring shall beautomatically charged so that the operating mechanism is readyfor closing immediately after the breaker trips. The mechanismshall be provided with a motor starter suitable for voltagespecified, complete with MPCB, thermal overload relay and power& aux. contactors. In case of pneumatic / hydraulic operatedmechanisms, sufficient quantity of fluid should be stored for atleast 5 ON / OFF operations. Absorbents shall be provided toremove moisture from air and keep it dry.

The required principal characteristics of the operating mechanismshall be as follows: -

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Remote Electrical Actuation

Local Electrical and Manual Actuation

Full making capacity with Manual Actuation

Mechanically and Electrically Trip-free operation.

Anti-pump feature

Interlocking (Mechanical or Electrical) against: -

* Operation with defective operating mechanism/ insufficientpressure of SF6 gas

* Closing operation during tripping

* Closing operation during closed state (blind stroke)

* Slow closing by operating mechanism

* Readiness for tripping after a closing cycle

* Constant making force

Closing or tripping cycle once initiated, independent of externalelectrical power source, the operation shall be completed.

Minimum mechanical shock on closing the breaker againstnormal, or against the rated short circuit current.

Simultaneous operation of interrupting elements in all phases.

Rugged mechanism-minimum maintenance.

Easy accessibility of components which require periodicmaintenance.

Key type interlocks to permit interlocking of breakers with anumber of disconnect switches.

Pneumatically Operated Mechanism

Pneumatically operated mechanism will obtain the supply from aunit compressed air system.

The operating mechanism will include necessary monitoring andsafety interlocks such as pressure gauges with alarm contacts forhigh/low/minimum and lockout pressure signals. The minimumoperating pressure will be such that the breaker will be capableof one operation if the breaker is in closed position before thelockout pressure blocks breaker opening/closing/reclosing.

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Independently adjustable pressure switches with electricallyinsulated contacts will be provided on the circuit breaker forpurposes of low and high pressure alarm and lockout in case ofinsufficient pressure to complete a closing, opening or reclosingduty.Local air receiver will be sufficient to carry out two COoperations.

Suitable interlocks for compressor start/stop will be arrangedwith air pressure gauge contact arrangements.

Hydraulically Operated Mechanism

Hydraulically operated mechanism will comprise operatingcylinder(s), set of actuating valves, high and low pressurereservoir, oil pump to charge the controls, comprehensivepressure monitoring and control system to regulate the operatingpressure, lockout arrangement to prevent operation below the

specified minimum operating pressure etc. A hand pump will alsobe provided for emergency operation.

The energy stored in the reservoir will be sufficient for O-t-COsequence of operation of the breaker. The closing lockoutpressure will be such that an opening operation is possible afterthe breaker is closed. In the event of pressure loss in thehydraulic system, the breaker contacts will remain in theparticular end position.

In case of failure of supply to the motor, the mechanism will be

capable of performing one sequence of O-CO operation.

The mechanism will be capable of operating the circuit breakercorrectly and performing the duty cycle specified under allconditions with the pressure of hydraulically operated fluid in theoperating mechanism at the lowest permissible pressure beforemakeup. The operating time at the lowest pressure for aparticular operation will not exceed the guaranteed operatingtime within the stipulated range of the trip coil supply voltage.

All oil piping will be of copper alloy and will be complete with

valves, expansion loops and other fittings as required.

1.2.8 CONTROLS AND AUXILIARIES

Electric motors, control devices, heaters, lights, closing and tripcoils shall be rated for voltages specified.

The spring winding motor shall have thermal overload protectionand shall be suitable for full voltages specified.All necessary control devices such as motor starter, auxiliaryrelays, indicating lights, local push buttons, limit switches etc.,shall be supplied with the equipment.

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An operation counter shall be provided with each operatingmechanism.

Minimum 10 NO and 10 NC site interchangeable auxiliarycontacts shall be provided for each pole. Any multiplication ofcontracts shall be done through electrical reset latch relay.

Starter, relay operating coils shall be of encapsulated type.

Plug in type auxiliary relays (similar to PLA/OMICRON etc) shallnot be used.

Local indicating lights shall be heavy duty (oil tight orequivalent), cluster LED type.

Local push buttons shall be heavy duty oil tight.

Space heater shall be controlled by adjustable thermostats of

adequate rating.

All control wiring shall be flame retardant thermoplastic insulatedand of minimum 2.5 sq.mm size.

All terminal blocks shall have stud type connectors. Terminalblocks should be capable of receiving 3 wires of 2.5 sq.mm andprovided with shorting links wherever necessary.

One grounding type duplex receptacle and a lighting fixture shallbe provided within the enclosure of operating mechanism.

ON/OFF switches of adequate rating shall be provided for thefollowing:

Control circuitHeatersSpring winding motor

Two local indicating lights shall be provided for the following:-

* DC control power ON

* Spring charged

1.2.9 OPERATING MECHANISM ENCLOSURE

The enclosure of the operating mechanism shall be of dust tightand watertight construction suitable for outdoor use.

The enclosure shall be made of either corrosion resistantaluminium sheet or steel sheet with highly durable finish. Hingeddoors shall be provided complete with handles, locks andminimum of 2 keys.

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In addition, means shall be provided for padlocking the doors inclosed position.

All gaskets shall be made of neoprene material.

All cover screws shall be made of stainless steel.All bolts, nuts and washers used for mounting of enclosure shall

be hot dip galvanized.

At the bottom of enclosure, a removable gasket blank plate shallbe provided for cable or conduit.

In addition, a Densimeter, a temperature compensated pressuregauge shall be provided at the base of the circuit breaker tomonitor the density and pressure of SF6 inside the enclosure andalarm and trip lock out switches shall be provided for pressuredrop.

Means shall be provided on the breaker housing for site filling ofSF6 gas in case of leakage.

Status of the operating mechanism such as pressure inside theair receiver, healthiness of compressor motor etc., shall beannunciated in the control room through potential free contacts.

1.2.10 NAMEPLATES

It will be the suppliers responsibility to provide adequatewarning and name plates.

Nameplates shall be provided at terminal blocks, relays, auxiliarycontrol devices etc., to provide adequate warning in case ofpresence of foreign voltage(s). Each breaker shall be identifiedby means of nameplate. Nameplates shall be fixed to the surfaceby means of countersunk-head stainless-steel self-tapping ordrive screws.

A separate data plate indicating the following shall be provided:

a) Sl No.

b) Type:c) Rated Voltaged) Highest system voltagee) Rated Currentf) Rated Insulation Levelg) Rated Frequencyh) Rated Braking Capacity (Symmetrical and Asymmetrical)i) Weight including Gas, Weight of SF6 gas/pole, for SF6 CircuitBreaker.

j) Rated Short time (3 Second) withstand current.k) Nominal SF6 gas pressure/density, for SF6 Circuit Breaker

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All auxiliary equipment necessary for the proper operation andmaintenance of the circuit breaker shall be supplied.

1.2.12 TESTS

Complete tests on the circuit breakers shall be made at thefactory by the supplier in accordance with the applicablestandards.

1.2.13 PAINTING

Enclosure except those made of aluminium or galvanized sheetsshall be painted with two coats of primer followed by two coats ofheavy finish paint. Paint colour shall be Pebble Gray, RAL-6032.

1.2.14 LUBRICATION

Provision shall be made by supplier for the lubrication of all partsrequiring same. The supplier shall furnish all necessary fittingsand special equipment.

The supplier shall recommend alternate lubricants which arereadily available locally.

1.2.15 SF6 GAS HANDLING UNIT

Evacuation, Refilling and Testing Equipment shall be supplied

with necessary tools and tackles and shall consist of thefollowing:

a) Vacuum Pump for evacuating the chambers to be filled withSF6 gas.b) Compressor with storage cylinder for storing SF6 gas ingaseous state at a pressure higher than the operating pressure inthe breaker.c) Purity and moisture measurement equipment.d) Gas regulator with manometer for filling gas in the breaker.

1.3.0 DOCUMENTATION

Drawings to be enclosed with bid.

Technical Catalogues for Circuit Breaker with detailedspecification

General arrangement drawing of breaker indicating overalldimensions, structure details, weight etc.

Detailed drawing of operating mechanism.

Schematic diagram.Page 9 of 34

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Drawings to be submitted after award of order.

G.A. drawing of breaker showing overall dimensions along withstructures and clearances for installation.

Dimensional drawing of terminal box and terminal connectors

Quality Assurance Plan

Test reports

Dimensional drawings for line and load side terminals.

Schematic diagram.

Outline drawing and sectional views showing the generalconstruction features of the breaker and operating mechanism

etc.

Maintenance manual

The contractor shall furnish the required number of copies ofinstruction manual for maintenance and commissioning of circuitbreaker.

1.4.0 CIRCUIT BREAKER TESTS

Type tests Test reports of all type tests as per IEC 62271 on

identical unit shall be furnished. If the type test report of theequipment is not available, the same shall also be carried out onequipment as per relevant standards.

Breaker shall be subjected to the contractors standard tests andto the routine tests specified in standards in the presence ofPurchaser or his representatives/consultant. However, thefollowing routine tests shall include as minimum.

1.4.1 AT WORKS

Insulation resistance test

Power frequency high voltage test for 1 minute.

Milli volt drop across circuit breaker terminals.

Operation tests at rated auxiliary voltage and pressure (30 makeand 30 break operations).

Measurement of resistance of closing and tripping coils.

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Tests to prove satisfactory operation of closing and trippingmechanisms at 80% rated voltage and 70% rated voltagerespectively.

Measurement of opening and closing time of breaker, both atminimum control voltage and normal control voltage.

Power consumption for closing and opening operations

Functional tests.

Physical inspection as per the approved drawings.

Tests to prove interchangeability of similar parts.

1.4.2 AT SITE

Insulation resistance test.

Milli volt drop across CB terminals.

Tests to prove correct operation of closing and tripping coils at80% and 70% rated control voltage respectively.

Operational and functional tests.

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2.0 ALTERNATING CURRENT, 220 kV DISCONNECT SWITCH

2.1.0 DESIGN CRITERIA

1. Reference Standard IS 9921 Parts I to V1982 / IEC Pub. 129 1975

2. Nominal system voltage 220 KV

3. Rated voltage of Isolator 245KV4. Rated frequency 50 Hz.5. System earthing Solidly grounded6. Voltage variation + 10%

7. Frequency variation + 5%

8. Design Ambient AirTemperature

50 C

9. Service Outdoor

10. Type Double break operated as per schedule of quantities

11. Rated continuous current 2000A12. Rated short time rating of

Isolator and earth switch40KA (RMS)

13. Rated duration of short circuitfor Main Isolator and earthswitch

3 Secs.

14. Rated peak withstand currentfor main Isolator and earthswitch.

2.5 times rated short timewith stand

15. Rated short circuit makingcurrent for main Isolator and

earth switch

100kA Peak

16. Rated temperature rise As per IS: 9921 Part II(1982)

17. Operating Mechanism Local: Manual & ElectricalRemote : Electrical

18. Control supply voltage forinterlocking solenoid and theelectrical operation

220 V DC

19. Rated voltage of motor/solenoid for electricaloperation

415 Volts, 3Ph, AC 50 Hz forMotor,230 V for space heater,

220 V DC for solenoid20. Operating voltage range for

the control supply70 120% of rated voltage

21. Operating voltage range forthe motor

85 110% of rated voltage

22. Permissible frequencyvariation

+ 5% of 50 Hz.

23. Earthing switch location To be provided as per theenclosed single line diagram.

24. Rated Mechanical terminalload for the main isolator andearthing switch

As per IS: 9921 (Part II)1992

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25. Rated Insulation level

a) Power frequency dryand wet withstandVoltage for 1 min. kVRMS

i) To earth and betweenpoles

460 kV

ii) Across isolating distance 530 kV

b) Lightning impulse withstand voltage kV Peak(Positive and negativepolarity)

i) To earth and betweenpoles

1050 kVP

ii) Across isolating distance 1200 kVP

26 Creepage distance of insulator

a) Total 31 mm per KV of highest

system voltageb) Protected Not less than half the total

creepage distance27. Thickness of galvanising of

metal partsNot less than 100 microns

28. Centre line distance betweenphases

4000 mm

29. Cantilever strength of insulator

As per IS: 2544

30. No. of auxiliary contacts onmain isolator

10 NO + 10 NC or more asper interlocking requirement

31. No. of auxiliary contacts onearthing switch

10 NO + 10 NC or more asper interlocking requirement

32. Interlock between isolator &earthing blade

Electrical / Electro mechanicalby means of blocking solenoid

33 Technical requirement for thelocal control cabinet forisolator and earth switcha) Installation Outdoor on structure /

pedestal mountedb) Enclosure Sheet steel, weather proof,

dust & water tight complete

with Canopy and guttersalong the canopy for drainingthe rain water

c) Auxiliary Supplies As given under Sl.Nos.18 & 19

34. The control cabinet shall include but not be limited to :

a) Open / close mechanical indicators for main isolator andearth switch.

b) Separate terminal blocks for AC power, control / DC.

c) MCBs for control supply.

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d) Reversing starter with MPCB, contactor, thermal O/Lrelay and forward / reverse contactors, lamps, limitswitches for electrically operated disconnect switches.The starters shall be mechanically and electricallyinterlocked.

e) Space heater with ON / OFF switch.

f) Cabinet illuminating lamp with ON / OFF switch andthermostat.

g) 3 Pin plug & socket with fuse.

2.2.0 TECHNICAL SPECIFICATION

2.2.1 Scope:

The scope of this specification covers Alternating CurrentDisconnect Switches with / without Earthing switch for ratedvoltage of 245 KV.

The disconnect switch shall comply with the latest revisions ofthe following standards.

a) IS 9921 Part I to V

b) IEC Publication No. 129 1975

2.2.2 Location:

The disconnect switch is required for lines, Bus coupler andtransformer feeders and will be located in the indoor switchyard.

2.2.3 Type of disconnecting switch:

The disconnecting switch shall be air break, triple pole, gangoperated, Double break as specified, with/without mechanicallyand electrically interlocked three pole earthing switch to earththe incoming / outgoing terminals of the main blade as per theenclosed single line schematic / Design criteria. The disconnectswitch shall be suitable for horizontal upright mounting onconcrete foundation or galvanized steel structures. Isolators withmovement of contacts in horizontal plane are preferred. Motor

operation wherever specified shall be provided for opening andclosing of disconnect switch and earth switch. In case of motoroperated disconnect switches, means shall be available formanual closing and opening of isolator as well as the earthswitch in the event of power failure. Mechanical and Electricalinterlock between the isolator and earth switch shall be availableboth in Manual and Electrical operation of the disconnect switch.

The disconnect switch shall be capable of interrupting smallinductive and capacitive currents such as those whiledisconnecting unloaded lines, charging current of cables or

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temperature limits mentioned in design criteria Further thedisconnect switches shall have rated short time withstand currentand Peak withstand current as specified in design criteria.

2.2.4 Earth switch:

The disconnect switch shall be provided with earth switch, as

specified, forming integral part. The rating of earth switch shallbe same as that of disconnect switch with respect to rated peakshort circuit current and making current and short time withstandcurrent. The earth switch shall be manually operated but shallbe electrically and mechanically (castle key interlock / Electro magnetic solenoid interlock) interlocked with the main switch andother isolators / breakers in the yard so that the grounding bladecannot be closed on to a live line / bus i.e. the grounding bladecan be closed only when the isolator is open and the isolator canbe closed only when the earth switch is open. Further in case ofdouble side earthing switches the earthing switch shall be

interlocked with the upstream isolator / Breaker throughSubstation Automation System.

2.2.5 Additional interlocks:

The disconnect switch shall be Electro magnetically interlockedwith the associated circuit breaker. Even manual operation ofdisconnect switch shall be possible only when the associatedbreaker is in the open position. The interlock shall be sodesigned that it shall not be possible to operate the disconnectswitch either locally or by remote control when the associated

circuit breaker is in the closed position. The interlock shall befool proof in all respects. The interlock relay / solenoid shall beprovided in the cabinet for operating mechanism.

2.2.6 Operating mechanism:

The operating mechanism for disconnect switch shall be suitablefor local manual and electrical operation and remote electricaloperation, as specified.

The three-pole isolator shall be provided with motor operated

group drive in addition to hand drive, wherever specified. Theoperating mechanism and its controls shall be so designed thatunder no circumstances, the switch blade travel is interruptedbefore it reaches the fully closed or open position. An auxiliarycontact shall be provided which will disconnect the motor controlcircuit during manual operation of the isolator unit. The motorshall be rated for voltage specified in design criteria. The motorshall operate for 120% of rated voltage satisfactorily, closing /opening the isolator at required speed. If supply voltage is notadequate for safe operation, necessary interlock to preventelectrical operation shall be provided. A signaling device for allpoles of the isolator and earth switch shall be arranged both forclosed and open position, to indicate isolator / earth switch

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position on remote panel in switchyard control room. Further themotor shall be provided with Electrolytic grade copper windingwith class F insulation with temperature rise restricted to Class B.

The manual operation should be easy but not easily accessible.There should be proper locking arrangement for manualoperation.

The operating mechanism shall have positive control of blademovements at all times and under most arduous conditions.Linkages shall be fitted free from slack and lost motion.

All bearings shall be heavy-duty type, lubricated for life andsealed against dust and moisture.

The manual operating handle shall be mounted on the basesupporting structure. Guide bearings shall be provided at aheight of 750 mm. above ground level. All brackets, angles,

guides, guide bearings and other members necessary forattaching the operating mechanism and operating handles tosupporting structure shall be supplied as an integral part ofdisconnect switch. The moving blades of isolator shall turn 90degree after making the contact for ensuring sufficient contactpressure. Flexible copper jumper connection shall be providedbetween the operating handle and the frame for earthing ofoperating handle. Further the earth switch shall also beconnected to the frame by means of flexible copper jumper. Thecross section of the Jumper shall not be less than 150 Sq. mm.

2.2.7 Operating cubicle:

A painted sheet steel, ground / structure mounted, weather proofand dust proof operating cubicle with hinged door and padlocking facility shall be provided for housing control equipmentand driving motor, reversible starter and interlock relays etc. Allwiring for the associated controls shall be terminated in thiscabinet. Auxiliary contacts of main isolating switch as well asearthing switch shall be wired to terminal block in this cabinet.Necessary double compression brass cable glands for power andcontrol cables shall be included in the scope of supply. Complete

wiring shall be with 650 / 1100 V grade, PVC insulated, 2.5Sq.mm stranded copper wires with numbered ferrules at bothends of the wire. Anti condensation space heater, illuminationlamp and 3 pin socket with respective ON / OFF switches shall beprovided inside the cubicle. DC, AC and power terminals shall besegregated. Further all the auxiliary contacts of the main switchand earth switch shall be wired to the operating cubicle. Inaddition about 40 to 50 spare terminals shall be provided in theoperating cubicle for interlocking purposes.

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The switchblade of main and earth switch shall be copper. Itshall be of one solid piece construction and shall be so assembledthat no part of the blade can move relative to the other. Thethickness and section of the blade shall be such that it retains itsform and straightness under all conditions of operation includingthe flow of system fault current for the period specified. It shall

also be capable of withstanding all torsional and bending stressesdue to the operation of switches.

The disconnect switch shall have high-pressure self-aligningadjustable contacts. The contacts shall be well protected allround by a metal cover which provides not only electrostaticscreening but also prevents coarse dust from entering betweenthe contacts. The contacts shall be designed such that thecontact pressure is released before any movement of blades inthe opening direction takes place and is applied after the closingtravel is completed. There shall be sufficient wiping action of the

contacts to make them self-cleaning.

The earthing switch of disconnect switch shall be complete withall parts that are necessary or essential for the efficientoperation. Such parts shall be deemed to be within the scope.

Disconnect switch and earth switch including their operatingmechanism and terminals shall be such that they cannot bedislodged from their open or closed position by gravity, windpressure, vibrations, shocks, etc., The rated mechanical load forthe terminals shall be as specified in the design criteria.

The disconnecting switch/earthing switch contacts shall be ofsilver faced copper. Further, to enable breaking of smallinductive currents of unloaded transformer as well as thecapacitive currents of unloaded lines/ cable charging current blowout coil shall be provided for each pole of the isolator.

All live parts shall be of non-rusting and non-corroding metal.Current carrying parts shall be of non-ferrous material such ascopper or aluminium. Bolts, screws shall be provided with lockwashers, keys or equivalent locking facilities and if provided on

current carrying parts shall be made of non-rusting and non-corroding metal such as copper.

Base channels and other structural members such as operatingpipes, phase coupling rods etc. operating mechanism boxes,bolts, pins etc., shall be hot dip galvanized. The thickness ofgalvanising shall not be less than 100 microns.

All similar parts shall be interchangeable.

The disconnect switch shall be such that no lubrication of anypart is required except at very infrequent intervals.

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During the course of normal operation, it is likely that thedisconnect switch/earth switch may be left in the open/closedposition for long periods.

Disconnect switch shall be such that it is free from visible coronadischarge in both closed and opened positions. Corona rings asnecessary may be provided.

The clearance between live parts and grounded structures shallnot be less than those specified in relevant standards. The inter-phase clearance shall be as per switchyard layout. The length ofbreak in open position shall be such that there is absolutely nopossibility of arc over from the live parts to the de-energizedparts on which any maintenance work may have to be done. Thespeed of opening or closing the switch shall be designed toensure that the arcing during the operation is reduced to theminimum.

2.2.9 Auxiliary contacts:

10 NO + 10 NC auxiliary contacts shall be provided for the mainisolator and 10 NO + 10 NC for earthing switch. It shall bepossible to convert NO to NC and vice versa at site. Theauxiliary contacts shall have a continuous current carryingcapacity of at least 10 Amps. All these contacts shall be wired tothe disconnect switch operating cubicle.

2.2.10 Insulators:

Insulators shall be made of high strength porcelain and shall besuitable for the service voltage and BIL specified. Further theinsulators shall be high creepage type with minimum creepagedistance as indicated in the specification.

Porcelain used for the manufacture of insulators shall behomogenous and free from flaws or imperfections that mightaffect the mechanical and dielectric quality. They shall bethoroughly vitrified, tough and impervious to moisture. Glazingof porcelain shall be uniformly brown colour, free from blisters,burrs and other similar defects. Insulators of the same rating

and type shall be interchangeable.

The porcelain and metal parts shall be assembled in such amanner that due to any thermal expansion differential betweenthe metal and porcelain parts throughout the range oftemperature variation shall not loosen the parts or create undueinternal stresses which may affect the electrical or mechanicalstrength and rigidity. Each cap and base shall be of high-gradecast steel or malleable steel casting and they shall be machinefaced smoothly and galvanized. Insulators shall be stack type.

2.2.11 Supporting structures for disconnectors shall be included in thecontractors scope of supply. The contractor shall furnish detailed

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dimensional drawings indicating weight and all fixing details andrelative locations of chassis, operating mechanism box andoperating handles etc. The contractor shall also furnishorientation GA showing positions of Main Blades and Earth Bladein open condition along with Control box.

2.2.12 Accessories:

a) Name Plate

Stainless steel / Anodised Aluminium nameplate shall beprovided on disconnect switches, earthing switches andoperating devices.

b) Grounding pads

Each pole of the disconnect switches shall be provided withtwo grounding pads at opposite ends, brazed to the base

channel. Flexible copper ground connectors shall beprovided for connecting operating handles of disconnectswitches and earthing switches to the grounding system.

c) Arcing horns

Suitable adjustable arcing horns made of tinnedelectrolytic copper shall be provided on disconnectswitches.

2.2.13 Auxiliary equipment

All auxiliary equipment necessary for the proper operation andmaintenance of the disconnect switches shall be supplied.

2.2.14 Testing

All isolators shall be mounted at works and at site and tested asper the detailed list of tests indicated elsewhere in thespecification.

2.3.0 Drawing and data to be submitted by Tenderer

The bidder shall submit along with his tender, the followingdrawings:

a) General outline and dimensional drawing of the completedisconnect switch assembly.

b) General arrangement drawing of the operatingmechanism.

c) Outline drawing of the insulators and supportingarrangement.

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d) Drawing of contacts.

e) Interlocking scheme.

f) Technical Catalogue of the Disconnection Switch/Earthswitch

Documents to be submitted after award of contract

a) General outline and dimensional drawing of the completedisconnect switch giving the net weight, shipping weights,loads and forces caused on the supporting structures.

b) Detailed drawing of the operating mechanism, auxiliaryswitches, earthing switches etc.

c) Detailed drawing of contacts

d) Location and mounting details of operating handles,operating devices and general arrangement of operatingcubicles.

e) Terminal stud detail.

f) Details of guides and guide bearings to be mounted onsupporting structure.

g) Schematic and detailed wiring diagram for the controlcircuit.

h) Detailed drawing of supporting structures

i) Quality Assurance Plan

j) Test Reports

k) rational and Maintenance manual

The supplier shall obtain the approval of the purchaser of theabove documents/data and work shall be carried out exactly as

indicated on the approved drawings and data and no alterationsshall be made without the written approval of the purchaser.

If any subsequent alterations are found necessary and approvedby the engineer all drawings and data affected by suchalterations shall be duly revised and resubmitted for the approvalof the purchaser as set above.

Suppliers drawings and data will be reviewed and approved onlyas to arrangement and conformity to specification and relateddrawing, and approval shall not be construed to relieve ormitigate the contractors responsibility for accuracy or adequacy

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& suitability of materials and / or equipment representedthereon.

On completion of the work, the supplier shall at his own expenseprepare and supply to the purchaser certified copies in requisitenumber.

a. Erection or installation manualb. Inspection and maintenance manualc. Operation manuald. List of supplied spare parts

2.4.0 TESTS

2.4.1 Type Tests

Test reports for the following type test as per IS 9921 Part IVcarried out on identical units shall be furnished along with the

tender. If the Type Test report of equipment of the same designis not available, the same shall also be carried out on equipmentas per relevant standards.

i) Test certificate for rated short circuit making current andthrough fault withstand for main isolator and earthingswitches.

ii) Test certificate for short time short circuit rating for themain isolator and earth switch.

iii) Impulse test certificate for the rated impulse levels.

iv) Current breaking Test certificate for the main isolator forcable/line charging, transformer no load and low inductivecurrents.

v) Temperature rise test on the disconnect switch for therated current.

2.4.2 Routine Test at Works

The following Routine tests at works shall be witnessed byPurchaser or his representative/Consultant.

i) Power frequency High voltage dry and wet withstandingtest for one minute on complete assembly.

ii) Power frequency HV test on auxiliary circuits.

iii) Measurement of contact resistance for the main isolator.

iv) Operational tests to prove satisfactory operation of theswitch interlocks and operating mechanism at minimum,rated and maximum voltage and frequency limits.

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v) Test for rated mechanical loads on the terminals.

vi) Test for rated values of maximum force required formanual operation.

vii) Test for specified thickness of galvanising on metal parts.

viii) Creepage distance and centre line distance measurementfor the complete switch assembly.

ix) Physical inspection of the disconnect switch complete withearth switch for all the accessories, fixing dimensions etc.

x) Insulation resistance measurement with High voltagemegger.

2.4.3 Test At Site

i) Measurement of resistance of main contacts

ii) Operation tests to prove satisfactory operation andinterlocking.

iii) Insulation resistance measurement with high voltagemegger.

iv) Visual inspection for any defects / damage.

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3.0 220 kV LIGHTNING ARRESTERS4.0

3.1.0 DESIGN CRITERIA

1. Type of arrester Station class Zinc oxide surgearrester.

2. Service Outdoor in polluted atmosphere with

carbon & conducting dust & withaverage design ambient of 50 C

3. Nominal system voltage 220 KV, 3 Phase 50 Hz, Effectivelyearthed.

4. Max. system voltage 245 kV5. Reference standard IEC 99-4 and IS: 3070-Part-3-1993

for housing.6. Rated voltage of arrestor 198 kV RMS7. Maximum continuous

operating voltage (MCOV)168 kV (RMS)

8. Nominal discharge 10 kA peak (heavy duty) current(8*20u sec wave)

9. Line discharge class Class 310. Maximum residual

voltage for 80*20 u secdischarge current of 10KA peak

550 kV peak

11. Maximum switching surgeprotective level

467 kV

12. Steep front currentimpulse residual voltagewith 1 micro second fronttime current wave of 10KA peak

605 KVP

13. Watt loss at MCOV 0.25 W / kV14. High current impulse with

stand (4/10 micro secwave)

100 KA peak

15. Pressure relief capabilityof the arrestor

Class A

16 Long duration currentimpulse rating

IEC class III

17. Temporary over voltagewithstand capability ofthe arrester for

0.1 Sec201 kV1 sec 195 kV

10 sec 185 kV100 sec 173 kV

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18. Creepage distance of theinsulating housing

a) 7595 mm of highest systemvolt

b) Protected (not less than halfthe total Creepage)

19. Impulse with stand levelof the housing

1050 kVP (1.2 x 50 microsec wave)

20 Power frequency withstand voltage of thehousing (wet & dry).

460 kV RMS

21. Switching impulse withstand voltage for ArrestorHousing

-

22. The thickness of galvanizing of metal parts

Not less than 85 microns.

3.2.0 SPECIFICATION:

3.2.1 Scope

The scope of this specification covers Lightning Arrestor withmaximum system voltage of 245 kV.

Lightning Arresters shall be provided in the following locations:

a) Near 400/220 kV Inter Connecting Transformersb) Near 220/11.5 kV Station Transformersc) For 220 kV LILO lines

Constructional features

The arresters shall be suitable for mounting on indoor structuresas specified. The arrester shall have adequate thermal dischargecapacity for switching surges, long duration surges and multiplestrokes. The arrester shall be capable of withstanding internalpressures developed due to the above discharges withoutoperation of pressure relief vents.

The arrester shall be provided with pressure relief devices, whichwill prevent shattering of porcelain in case of excessive gas

pressure build-up.

The insulator housing of the arrester shall be of porcelain withhigh mechanical strength and rigidity suitable for operation undersite conditions.

All metal parts shall be non-rusting and non-corroding material.Bolts, screws etc, shall be provided with lock washers.

3.2.2 Accessories:

Insulating base shall be on each complete arrester unit.

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Grading Ring

Grading ring shall be provided on each complete arrester unit forimproving voltage distribution on multi unit arresters.

Terminals

Line and earth terminal connectors and clamps shall be suppliedwith the lighting arrestors.

Name Plate

Earth lightning arrester shall be provided with a stainless steelnameplate in accordance with IEC-99-4.

Surge Monitors

Surge monitors connected in series between lightning arrestersand ground shall be provided to determine the serviceperformance and on-line condition of the lightning arresters.Surge monitors shall be provided with counters and leakagecurrent meters to record the number of operations performed bythe arrester as well as the leakage current in the arresterhousing. It shall be ensured that the connection of surgemonitor does not affect the protection requirement of thearrester.

3.2.3 Galvanised steel supporting structures for Lightning Arrestors

shall be included in the scope of supply. The contractor shallfurnish detailed dimensional drawings including weight and fixingdetails.

3.2.4 Drawings/Documents

Following drawings/Documents shall be submitted for approvalafter award of contract.

* Dimensional drawing of the arrester showing overall andmounting dimensions, clearances for installation and

mounting base plate details.

* Dimensional drawing of line and earth side terminals.

* Dimensional drawing of the lightning arrester structure.

* GA drawing of structure with design calculations.

* Operation and maintenance manuals.

* Test Reports

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* Dimensional drawings for supporting structures

3.2.5 Tests

Type tests Test reports of all type tests as per IEC on identicalunits shall be furnished. If type test report of the same design is

not available, the same shall also be carried out on equipment asper relevant standards.

Complete tests shall be carried out on lightning arrester andarrester housing as per IEC 99-4 and IS 5621-1980 at works.

Routine tests shall be carried out on all the units as perstandards.

Acceptance tests shall be carried out on minimum 2 units/ or asper IS 3070.

Following acceptance tests and routine tests shall be performedon the lighting arrester as minimum.

i) Acceptance tests (on minimum 2 units)

(Applicable standard IEC 99-4 and IS: 5621)

a. Residual voltage test at thenominal discharge current onthe complete arrester or

sections.b. Temperature cycle test onporcelain housing

Test certificate shall befurnished.

c. Porosity test on porcelainhousing.

d. Galvanising test on metal partse. Visual examination of porcelain

housing.f. Power frequency reference

voltage testsg. Dry and wet power frequency

withstand test on the housing.h. Measurement of Creepage

distance. (Total and protected).i. Test on surge counter and

leakage current meter.

ii) Routine & Acceptance tests on all units shall be carried out inthe presence of Purchaser or his representative.

a. All acceptance tests except b, c& d

b. Tests to prove satisfactory

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operation of counter andleakage meter.

c. Physical inspection as perapproved drawings.

4.0 INSTRUMENT TRANSFORMERS

4.1.0 DESIGN CRITERIA CURRENT TRANSFORMER

1 Standard IEC Publication 185/IS 2705

2 Voltage rating 220 KV3 System earthing Neutral effectively earthed4 Highest system voltage 245 kV5a Rated continuous current and

CT ratioAs per requirement

B Rated secondary current 1 Amp6 Short-time thermal current 40 kA, 3 sec.7 Dynamic peak withstand

current rating

100 kAP

8 Class of insulation A 9 Temperature rise above

ambient of 50o C - oil at top ofhousing (measured bythermometer)

35o C

Winding (measured by increasein resistance method)

45 0C

10 Accuracy class and BurdenCore 1

Refer SLDCore 2Core 3

Core 4Core 5

11 a) Oil level gauge and pressurereliving devices

Shall be provided for CTs

b) Pressure Gauge for nitrogenPressure for Hermetic Sealing

Shall be Provided

12 Installation Indoor, Structure mounted13 Accessories Terminal pad with clamps and

connectors for aluminium tubeindoor type weatherproofterminal box for CT secondaryconnection.

14 Insulation level Lightningimpulse withstand voltage(1.2x50 micro sec.) betweenprimary & secondary, primaryand earth

1050 KV Peak

15 1 min. p.f. withstand voltagea) Primary and Secondary,

Primary and Earth460 KV (RMS)

b) Secondary & Earth 4 KV (RMS)c) Creepage distance Not less than 31 mm/KV of

highest system Voltage16 BDV of oil (2.5mm gap) Not less than 80 kV RMS

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4.2.0 DESIGN CRITERIA CAPACITIVE VOLTAGE TRANSFORMER

1 Standard IEC Publication 186A/IS3156

2 Voltage rating 220 kV/3, Single phase3 Nos

3 System neutral earthing Neutral solidly earthed

4 Highest system voltage 245 kV5 Number of secondary windings Three6 Voltage ratio 220 kV/3 / 110V/3 /

110V/3/ 110V/37 Connection group Star / Star / Star/ Star8 Rated burden to be not less than As per requirement with

15% additional margin9 Class of Accuracy/short time

thermal current rating for 3 sec.0.2 /3P / 40 kA

10 Voltage factor 1.2 continuous/ 1.5 for30 sec

11 Phase angle error + / 20minutes12 Class of insulation A 13 Temperature rise over ambient of

50 COil at top of housing (measuredby theremometer)

35 C

Winding (measured by increasein resistance method)

45 C

14 Insulation level Lightning impulsewith stand voltage (1.2X50 micro

sec) between primary &secondary and primary & earth

1050 kV Peak

15 1 min. p.f. withstand voltagePrimary and Secondary, Primaryand Earth

460kV (RMS)

Secondary & Earth 4kV (RMS)Creepage distance Not less than 31mm/kV

of highest systemvoltage

16 BDV of oil (2.5mm gap) Not less than 60 kV RMS17 Installation Indoor

18 Accessories Terminal pad for O.Hline conductor outdoortype weatherproofterminal box forsecondary connectionOil level gauge, pressurerelief valve and pressuregauge monitoring thenitrogen pressure forhermetic sealing of thePT enclosure

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NOTE: Terminal connectors suitable for ACSR conductor / IPSaluminium tubes as indicated at the time of approval ofdrawings shall be provided. Suitable connectors for earthterminals shall also be provided.

4.3.0 TECHNICAL SPECIFICATION

4.3.1 CURRENT TRANSFORMERS

The current transformer shall be indoor type, single phase oilimmersed /SF6 filled and self cooled independently mountedtype. CTs shall conform to this specification and IS 2705.

The cores shall be of high grade, non-ageing electrical siliconlaminated steel of low hysterisis loss and high permeability toensure high accuracy at both normal andover currents.The CTs shall be hermetically sealed by nitrogen to prevent entryof air and moisture from outside. Pressure Gauge shall be

provided to monitor the pressure of nitrogen. These shall beprovided with pressure relieving device capable of releasingabnormal internal pressures. The saturation factor of the core formetering shall be low enough not to cause any damage tomeasuring instrument in the event of maximum short circuitcurrent.

The current transformer cores to be used for protection andrelaying shall be of specified accuracy suitable for differential orover current protection.

The rated burden of the current transformer shall be as indicatedin Design criteria. However, 15% additional burden shall be

considered for future expansion.

The quantity of the insulating oil - for first filling in each CT shallbe supplied by the supplier. The oil shall conform to therequirements of IS -335. Oil level gauge shall also be provided.

All the flanges, bolts required for mounting CTs and supportingstructure should be galvanized. The base of CTs shall be atheight more than 2.5m from ground level.

The secondary terminals including the tapping terminals shall bebrought out in a weather proof terminal box on side of CT for

easy access. Secondary terminals shall be provided with shortinglinks.

Dust, weather and vermin proof outdoor type terminal box foreach set of 3 phase CTs of each circuit shall be provided withsufficient number of terminals. Provision shall be made in theterminal box for entry of cables for taking in/out of the CT leads.Test links inside the box shall also be provided. All the terminalsfrom the terminal box of each phase CT shall be wired to thiscommon terminal box,

The insulator housing for the current transformer shall be madeof wet process from electrical grade porcelain and free from all

defects. Clearance and creepage distance shall be as specified.

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The housing used shall be of high Creepage, high strength typesuitable for heavily polluted atmosphere.

Terminal connectors suitable for ACSR conductor/IPS aluminiumtubes as indicated at the time of approval of drawings shall beprovided. Suitable connectors for earth terminals shall also beprovided.

Galvanised steel supporting structures for CTs shall be includedin the scope of supply. The contractor shall furnish detaileddimensional drawing including weight and fixing details.

4.3.2 CAPACITIVE VOLTAGE TRANSFORMERS (CVT)

Constructional Features

Voltage transformers shall be single pole unit designed for uprightmounting on steel structure and furnished complete with anchoringhardware.

Insulator shall be wet process porcelain, brown glazed and freefrom imperfections. All metal parts and hardware shall be hot dipgalvanized.

Creepage distance shall correspond to very heavily pollutedatmosphere (31mm/kV). Grading ring, if required, shall beprovided to maintain voltage gradient within permissible limit.CVT shall comprise a number of capacitor units mounted on asteel base containing the potential device and other accessories.

The capacitors shall be oil-impregnated type enclosed in an inert

gas atmosphere within porcelain shell hermetically sealed.

Accessories housed in the steel base shall include

a) Series reactor, which along with the capacitance of thedivider shall be tuned to power frequency.

b) Device for ferro-resonance suppression.

c) Protective gap for over voltage.

CVT shall be designed to cover its rated output range without any

adjustment of its electromagnetic unit and also to provide requiredaccuracy level upto the rated burden. CVTs shall be designedto perform transient response requirements as per relevantIS/IEC i.e. during transient oscillations following a short circuit onprimary side, the secondary output voltage shall not fall to a valueless than 10% of peak value before short circuit within 20 milliseconds.CVTs to be used with PLCC system with frequency range 40 to 500kHz shall be suitable for carrier connection. The carrier lead shall bebrought out of steel base through high frequency bushing. Carrierterminal shall be kept earthed, if not used.

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Measurements of magnetizing current, knee point voltage andsecondary winding resistance.Ratio test

Verification of terminal marking and polarity.Physical inspection as per the approved drgs.

Inter turn over voltage test

At site


Ratio test.

Measurement of terminal marking and polarity.

Inter turn over voltage test

4.4.2 Tests on CVT

At Works

Insulation resistance test

Power frequency HV test for 1 min.

Tests to prove accuracy class at rated burden.

Verification of terminal markings & polarity

Physical inspection as per approved drawing.

Ratio test.

At site


Verification of terminal markings & polarity

Ratio test.

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5.0 CONDUCTORS

A. ACSR conductor designation MOOSE1 Reference standard IS 398-19762 Stranding and wire dia

a) Aluminium 54/3.53b) Galvanized steel 7/3.53

3 Nominal copper area, sq. mm 3254 Equivalent Aluminium area sq.mm 5205 Resistance at 200C ohm/km < 0.055966 Ultimate tensile strength of conductor

kg/km159.60

B. IPS Aluminium Tubular Bus Bar

1 Reference standard IS 50822 Material of the tube Aluminium alloy

63401 WP, half hard3 Nominal dia of the pipe 4.0 Inches, schedule

404 Maximum temperature rise at rated

current450C

5 Rated voltage of the system in whichthese tubes are used

220KV, 50HZ,3 Phase

6 Highest system voltage 245KV, 50HZ, 3Phase

7 Max short circuit level of the system 15000 MVA, 3 Phasefor 3 seconds (40 kARMS)

8 Permissible temperature rise over 650C atthe end of short circuit

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String Insulators

Parameter ValueApplication Tension/suspensionApplicable standard IS 731No. of unit insulators in string 15 minimumDry flashover voltage, kV RMS 750

Wet flashover voltage, kV RMS 595Impulse flashover voltage,kV,RMS

1050

Unit Insulator rating, type 11 kV, Disc type

Tests at works : As per IS

Tests at sites : Physical inspectionThe tenderer shall include all required connectors, clamps,fittings etc required for the erection of the overhead line, tubularconductors and insulators. The contractor shall verify that the

buses which are used in tension and overhead ground wire shallbe free from joints or splices. The equipment used for stringingthe conductors and overhead ground wires shall be such that theconductors are not damaged or injured. All sections ofconductors damaged by the application of gripping attachmentshall be replaced before the conductors are pegged in place. Alldata such as stringing tables given tension with temperaturevariations shall be supplied by the contractor for approval.

The contractor shall be responsible for supplying and installingthe various conductors required for connection of various

equipment including bolts, nuts and washers required forinstallation. All connections etc., shall be so made that stressbetween connecting terminals will be reduced to minimum.

The physical layout of the system shall be such that the systemextension can be carried out with minimum changes.