TECHNICAL SPECIFICATION FOR 630 AMP 20KA 433 VOLTS L.T. SWITCH BOARD

1.0 STANDARDS

The switchboard shall conform to following specifications latest amendmentsthereof:-

(a) IS-2516 (Part I&II/) Specification for alternating current C.B. Sec.I )

(b) IS-4237 General requirements for switchgear andControlgear for voltages not exceeding 1000Volts.

(c) IS-6875 Control switches (Switching devices for controland auxiliary circuits including Bidder , Controlswitches (Switching devices for control andauxiliary circuits including Bidder , AC & 1200VDC)

(d) IS-2705(Pt-II) Specification for current transformers.

(e) IS-1248 Specification for direct acting electrical indicatinginstruments.

(f) IS-8623 Specification for factory built assemblies ofswitchgear andcontrolgear for voltage up to and including 1000V AC and 1200V DC.

(g) IS-8623(Pt.-II) Particular requirements for bus bar trunkingsystem.

(h) IS-375 Markin and arrangements for switchgear bus barsmain connections and auxiliary wiring.

2.0 LT SWITCH BOARD REQUIREMENTS

2.1 The details and arrangement for the incoming and outgoing feeders on the L.T.switchboard shall be as per enclosed sketch no.I

2.2 Front operated L.T. switchboard shall be operative on 433± 10% volts, 3-phase, 4 wire, 50 ± 5%Hz grounded A.C. system having a rupturing capacity of not less than 20KA at rated operating voltage.

2.3 The board shall be made of MS sheet steel clad totally enclosed ,dust andvermin proof,

2.4 Cubicle suitable for indoor floor mounting with separate compartments for

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individual feeders.

2.5 Neoprene rubber gasket shall be used at all joining surfaces to achieve dust tightand vermin proof sealing.

2.6 The switchboard shall be of sheet steel construction with M.S. sheet not lessthan 3mm, thickness. Frame work shall be rigid without using any externalbracings.

2.7 The switch board shall be designed to facilitate inspection/cleaning/repairs.

2.8 All equipments, bus bars with covers removed and other connections shall beeasily accessible from the back or front. No live parts of switch shall beaccessible unless it has been put in ‘OFF’ position.

2.9 All switches shall be suitable for front on board operation and interlocked withthe doors.

2.10 The design of switchboard shall be such that it covers minimum floor space, however, ample space shall be provided in the cable duct for accommodating PVC insulated aluminum conductor cables with enough space for carrying out jointing works etc.

2.11 Brass cable glands, suitable for PVC aluminium conductor cable of sizes, as pertable A&B shall be provided for all feeders.

2.12 Switches shall be placed in multitier arrangements, below with common bus bar chamber ,the switchboard shall be complete with foundation bolts ,small wiring wherever required, earthling strips upto nearest earth bar etc. Bimetallic connectors shall be used where aluminium to copper or vice-versa connections are required.

2.13 BUS BARS

i) The bus bars shall be made of copper with PVC sleeving having rectangularcross sectional area of one square inch. These shall be adequately designed and supported to withstand the electrodynamic forces arising from a short circuit in the system.

ii) Vertical bus bars shall feed the outgoing feeders. These shall be completely enclosed and adequately ventilated. It should be possible to work on the circuit outgoing connections with out any danger of accidental contacts with the live connections between vertical bus bar and circuit terminal.

iii) The bus bar chamber shall be adequately ventilated and shall be provided with removable covers for easy access. The bus bars shall be PVC sleeved /taped except at T-off joints. At T-off joints sticking tape /molded tape shall be used. Connections between vertical bus bars and circuit terminals shall preferably be fully insulated or enclosed so as not to leave any exposed live parts. However these shall not be considered for any uprating of the bus bar current rating due to sleeving / taping.

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iv) The bus bar should be taped with suitable colour code for ready identification ofphases.

3.0 AIR CIRCUIT BREAKERS

3.1 Tripple pole air circuit breakers shall be trip free manually operated horizontaldraw out type fitted with mechanical ON and OFF indicator.

3.2 The A.C.B. should be designed for quick make and quick break operations andshall be fitted with C.T. operated thermo magnetic release for over load andshort circuit protections.

3.3 The detailed specification of air circuit breakers are as follows:-

I Breaking capacity shall not be less than 20KA at rated operating voltage andbreaker shall be rated for 630Amp.continuous.

II Set of mechanical interlocks with automatic safety shutter gear for completelyshielding the stationary contacts, when breaker is removed.

III 1 no. auxiliary switch.

IV 1no. neutral link

V 1 set of contacts to give audible and visual (mechanical flag indication) alarm incase of tripping of the circuit breaker on fault with alarm bell and cancellationswitch.

VI 3nos. C.T. 400/5A for metering having accuracy class 1 and instrument securityfactor 5.

VII 3nos current transformer of ratio 400-200/5.15VA burden and accuracy class 5P10 for protection.

VIII 1 no, flush mounted voltmeters.

IX 1no. Voltmeter selector switch.

X 1no. flush mounted ammeter suitably scaled.

XI A meter selector switch.

XII Suitable for 3 cores, 400sq.mm. PVC cable split type cable terminal box.

XIII Push button for emergency tripping.

XIV Lable inscriptions, terminal boards and instruments fuses etc. All equipmentsand fuses etc. mounted on circuit breaker cubicle should be properly wired according to the equipments.

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The CTs ammeter and voltmeter etc. shall be of reputed make well tried and proven by actual use. Terminal block shall be of Kirlkoskar-Asea or Easun make.

The A.C.B. shall be of CG- Schienider/ LARSEN AND TUBRO/ ALSTOM make.

4.0 MOULDED CASE CIRCUIT BREAKERS / ISOLATOR

4.1 The MOCB / isolator shall be suitable for flush mounted sheet steel clad, totallyenclosed, cubicle type switchboard. It shall be possible to remove the switch forinspection or replacement from the face of the switch board such thatconnecting wirings are not disturbed.

4.2 The rupturing capacity of each MCCB/ Isolator shall not be less than 20KA atrated operating voltage.

4.3 Making current capacity of MOCB shall be twice the short circuit rating

4.4 The MOCB shall be manually operated with mechanical ON/OFF indicator; itshall be quick make/quick break type and trip free.

4.5 The MOCB shall be provided with tripping device with inverse time current characteristics for overload protection and device for instantaneous protection against short circuits.

4.6 The mounded case circuit breakers/isolators shall be of CG-Schiender/LARSEN AND TUBRO/ ALSTOM make, L.T boards shall have ACB andMOCB of same make only.

5.0 DETAILD SPECIFICATION FOR L.T. SWITCHBOARD

5.1 This switchboard is proposed to be installed at132KV substation for distributionof L.T. supply as per single line diagram shown in the enclosed sketch No.-1.

5.2 This switchboard shall be fed through two incoming circuits. The bus isolator on the switch board shall be mechanically and electrically interlocked with the incoming switched on the board such that bus isolator is not closed if supply is being fed through both the incomers. However, in case of failure of supply it shall be possible to energise the complete bus bar of the switchboard through either of the incoming switch.

5.3 The main bus bar shall be of 800 Amps, rating for phases and 400 Amp. forneutral and shall have following circuits:-

1. Incoming circuit with 630Amp.ACB-2 Nos.2. Bus isolator 630Amp.rating moulded case type-1 No.3. Out going circuit with MOCBs of desired rating for following feeders.

MOCB Thermal No. Cable terminals to be suitable for.Rating setting of of

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MOCB of fdrs.Fdrs.

200Amp. 125 Amp. 1 95sq.mm. 3-1/2 core PVCAlumcable

100Amp. 063Amp. 6 50sq.mm. ---------do----------100Amp. 040Amp. 2 50sq.mm. ---------do----------

5.4 Neutral termination of each incoming and out going feeder from L.T.Switchboard should be done through a link provided adjacent to respectiveACB/ MOCB.

6.0 ALARM SCHEME

6.1 110 volts DC operated suitable audible and visual (Mechanical Flag indication)alarm scheme shall be provided to indicate tripping of ACB-1,ACB-II and MOCBs. (common). There should also be 3 sets of audible and visual (Mechanical flag indication) alarm for station transformer indications viz Buchholz alarm, winding temperature high alarm.

6.2 The switchboard shall be provided with following indicating lamps:-

i. Coloured Red to give CB closed indication.ii. Coloured Green to give “C.B. open” indication.iii. Coloured Yellow to give “DC supply healthy indication.

Schematic diagram giving the details of operation of the required alarms and mechanical Flag indication have been shown in the sketch no. II enclosed.

7.0 TESTS

The successful Bidder shall be required to carry out the following tests at their works free of cost.

7.1 ASSEMBLY AND TEST AT MANUFACTURER’S WORKS

The L.T. switchboard and other associated equipment shall be assembled at the manufacturer’s works and shall be subjected to routine and other acceptance tests specified in the latest relevant Indian Standard specification, Four copies of the certificates of the routine and acceptance tests on all the equipments shall be furnished by the Bidder to the “Engineer of the Contract” before dispatch for his approval showing that the L.T. switchboard has been tested and has been found to be sound electrically and mechanically and is in working order in all respect and that it complies with the terms of the order . The Bidder shall also provide facilities for the inspection of the routine and acceptance tests by the representative of the Purchaser, if so required. In addition to above routine and acceptance tests, the Bidder shall carryout temperature rise test on one of the L.T. switchboard of each category free of cost and shall submit test certificates for approval of the Purchaser. In respect of all bought out components test certificates of their manufacturer must be submitted to the Purchaser. Details of these manufacturers shall be furnished to the Purchaser well in advance.

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(1) CIRCUIT BREAKERS

Type test certificates on one breaker of each type i.e. ACB and MOCB of different rating shall be supplied. Routine tests shall be carried out on all the breakers which are to be supplied.

(2) SWITCH BOARD

Each component parts of the L.T. switchboard and other associated equipments shall be assembled and tested for accurate assembly and satisfactory operation at manufacturer’s works before dispatch.

(3) INSTRUMENT TRANSFORMERS

All instruments transformers shall be subjected to tests at manufacturer’s works in accordance with relevant Indian Standard Specifications. Ratio and phase angle calibration curves shall be submitted for each type. Copy of test certificate from manufacturer of these instrument transformers shall be supplied.

(4) METERING INSTRUMENTS

High voltage tests shall be carried out on all meters. Accuracy tests and calibration curves shall be submitted for one instrument of each type.

(5) TEST AT SITE

The Purchaser reserves the right of carrying out at site such tests as he may decide upon, provided the test levels are within the limit laid down in Indian Standard Specifications. Such test shall be carried out in consultation with the Bidder and shall be at the expenses of the Purchaser.

8.0 LABELLING

The equipment shall be dispatched fully labeled describing type ,make, rated voltage ,frequency ,current rupturing capacity, this office Bid specification no, year of order and substation for which purchased etc.

9.0 INTERCHANGEABILITY

All parts shall be made to standard gauge wherever possible so as to facilitate replacement and repair. All corresponding parts of similar apparatus shall be interchangeable.

10.0 PAINTING

The switch board shall be synthetic enamel painted in light grey as per shade no.631 of ISS. To achieve a durable finish, careful surface pretreatment shall be carried out at per following process:

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i. Removing of rust and corrosion by treating all sheet metal with acid.

ii. After acid treatment rinsing with cold water for removing traces ofacid.

iii. Rubbing and cleaning with sand paper for complete removal ofscales/rust,if any.

iv. Rinsing with cold water for a final cleaning.

v. Air drying completely.

vi. Spraying of one coat of best quality zinc chrome primer on dry sheet.

vii. Removing minor surface flaws by rubbing and applying putty after firstcoat has air dried.

viii. Spraying of one coat of air drying synthetic enamel paint light graycolour as per shade no.631 of ISS of best quality ICC make.

ix. Spraying of 2nd, zinc chrome primer.

x. Removal of surface flaws by applying putty and rubbing the sheet steelto a smooth level after the first coat has sufficiently air dried.

xi Spraying of final coat of air drying synthetic enamel paint of shadeno.631 of IEC make .

xii Half liter paint of the same shade shall also be supplied with each board for final touch of boards or any minor scratches caused during transportation.

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