SPECIFICATION FOR PROCUREMENT OF NON INDUCTIVE RESISTOR BANK FOR IMPROVEMENT OF POWER FACTOR DURING SHORT CIRCUIT TEST

APPLICATION

Non inductive resistors are required to be used in series with current limiting reactors in 2500

MVA High Power Lab at Central Power Research Institute, Bangalore to improve the power factor

during short circuit tests.

SCOPE

Scope of the works covers design fabrication, testing, installation and commissioning of 3 Nos.

resistor banks suitable for 36 kV system voltage.

SERVICE CONDITIONS:

The complete system supplied against this specification shall be suitable for satisfactory

continuous operation under the tropical conditions.

1. Altitude : 921 meters above MSL

2. Ambient temperature : Min-10°C, Max-45°C

3. Relative humidity : 90%

4. Installation : Indoor

TECHNICAL SPECIFICATION

The resistor banks shall be used for improving the short circuit power factor of the 2500

MVA High Power Lab. As the station power factor is predominantly inductive (around

0.03). Resistor banks should be non inductive and should be fabricated using stainless

steel sheets. The resistor bank made out of cast iron is not acceptable.

The supplier should offer resistor bank with stain less steel of grade AISI-304 and AISI-

406 separately

1. The resistor bank shall be suitable for 36 kV system voltages and shall withstand the

following insulation levels.

a) Rated voltage : 36 kV (phase to earth)

b) Rated power frequency one minute

withstand voltage (dry) kV : 70 kV rms

c) Rated lightning impulse withstand voltage : 170 kV Peak

d) Minimum clearance between live part to earth : 280 mm

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2. The resistor material shall have a stable and steady temperature coefficient of resistance.

3. The resistor material shall be resistant to corrosion.

4. The resistor element shall be designed to carry rated short time current of 16kA

rms/40kApeak for rated operating sequence without exceeding temperature limits.

5. The resistor bank shall be bolted on angles welded to angle iron structure.

6. Suitable insulation between resistance element and supporting tie rod is to be provided.7. The tie rod is insulated from the supporting structure by suitable cast resin insulators

8. The resistor bank shall be placed on stand off insulators with insulation level of 36kV.9. No enclosure is required for the resistor bank10. Forged Eye bolts shall be provided for lifting and transportation.

Resistor bank shall be mounted on racks. Due to the limited space available, the dimensioning of

the banks shall be such that it can be accommodated in the space provided for resistor bank

(0.75mtr width X 1.4 mtr breadth X 2.5 mtr height

The resistor bank shall be designed to withstand the electro dynamic forces produced during the

period short circuit current flows through them. Resistor bank shall be able to withstand short

circuit current during the following operating sequence.

C-0.1 sec.-O-0.3 sec.-C-0.2 sec.-O-3 min.-C-0.2 sec.-O

Such six cycles shall be repeated during 1 hour period. The temperature during a complete

sequence of 1 hour at rated short circuit current shall not increase more than 100°C.

RESISTOR BANK RATING AND CONFIGARATION

Each resistor bank shall consist of 6 tiers of resistor rack assemblies. Each tier of resistor shall

have a value of 70 mΩ (+5% - 0%) with tapping at 64 mΩ on each rack. Provision may be made

to bring out tapping point along with other two terminals of each rack of the resistor bank at the

terminal board.

The resistance assembly of 70 mΩ shall be able to withstand 16 kA rms for duty cycle specified

above with peak withstand current of 40 kA. The terminals of all the 6 resistances and the tapping

at 64 mΩ shall be brought out on front panel on a bakelite board of thickness not less than 15 mm

for making series and parallel combination. Series and parallel combination shall be made in such

a way so that same links can be used for making series and parallel combination.

When all the 70 mΩ resistor assemblies are connected the rating of the bank shall be as under.

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Resistance assemblies connected in Resistance value (+5% -

0%)

Short time current rating kA rms / kA

peak withstand current

All in series420 mΩ 16/ 40

All in series with 64 mΩ tap384 mΩ 16/40

All in parallel with 70 mΩ11.67 mΩ 80/200

All in parallel with 64 mΩ tap10.67 mΩ 80/200

Three racks of 70 mΩ in series, two such combination in parallel 105 mΩ 32/80Three racks of 64 mΩ tap in series, two such combination in parallel 96 mΩ 32/80Two racks of 70 mΩ each in series three

such combination in parallel 46.7 mΩ 45/113Two racks of 64 mΩ tap each in series three such combination in parallel 42.67 mΩ 45/113

Each resistor bank shall have, two main busbars of short time rating 40 kA for 1 sec 100 kA peak.

The resistor bank combination indicated above shall be connected to these busbars.

All links for series and parallel combination shall be supplied by the manufacturers.

SCOPE OF SUPPLY:

1) Resistor banks each consisting of 6 tiers – 3 Nos.

2) Bus bar links along with insulators – 3 sets.

for connection of each resistor bank

to the incoming and outgoing bus bars

Tests: the following test shall be carried on each resistor bank.

1) Measurement of resistance of resistor bank and sub assemblies.

2) HV test

Before commencement of supply, one resistor bank shall be tested for short circuit test. The duty

shall be as per specified duty of the specification. The test shall be conducted in the following

combination:

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- All 70 mΩ resistors with tapping at 64 mΩ connected in series i.e. total resistance 420

mΩ/384 mΩ, to be tested at 16 kA rms and 40 kA peak value. In this combination one

sequence of duty cycle shall be conducted.

After tests the resistor bank shall be examined for any breakage or damage or deformation.

- Resistance value of each of the resistor bank shall be measured and its value shall

not show any significant change from initial measured value.

- Resistor bank shall be subjected to HV tests.

- Temperature rise during the duty cycle shall not exceed the specified value of 100°C.- No element of the resistor space shall get deformed or broken.

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QUESTIONNAIRE

1.0 Type of resistor bank (material) with Grade : Stainless steel

2.0 Rated voltage ( phase to earth) : kV rms

3.0 Rated thermal current of each resistor rack in the bank : Amps

4.0 Rated insulation level

a) H.V. dry power frequency withstand voltage / 1 min : kV rms

b) Lightning impulse withstand voltage : kV peak

5.0 Resistance of each assembly in the bank : milli ohms

6.0 Continues current rating, size and weight of : Amps, kgindividual resistor element

7.0 Short circuit withstand current of each rack :kA rms assembly in the bank for the duty cycle

specified in the specification

8.0 Configuration of terminal connections :please give separatelybrought on front panel for series parallel connections as well as for tapping for 240 mΩ

9.0 Phase to earth clearance :

10.0 Dimension of terminal connections of each resistor bank :

11.0 Size and thickness of bakelite plate used for terminal board :

12.0 Dimensions of main bus bar of each resistor bank :

13.0 Details of bushings used on bakelite board :

14.0 Short time current rating of main bus bars of resistors bank :

15.0 Number of support insulators and its :rating provided for 20 kA bus bars used for making series / parallel combination of sub resistors.

16.0 Tests :

Please specify the test to be conducted:

Contd.

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a) Measurement of resistance of each bank : YES / NO

b) H.V. dry power frequency withstand test : YES / NO

c) Lightning impulse voltage withstand test : YES / NO

d) Short circuit test for the duty specified in the specification : YES / NO

17.0 Any other special features of the resistor bank :

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