4 Kv System

Question 1

Why does AUX XFMR 1-2 have one coil powering 4 kV bus E and the other coil powering 4 kV bus D, F, G and H?

Answer 1

E has two condensate booster pump sets and the HDP , which combined total more load than all loads the other buses can carry.

Question 2

What conditions must be met to open 4 kV non- vital S/U feeder bkr?

Close 4 kV S/U feeder bkr?

Answer 2

Open- take to open

Close- synch switch on
- take to close

Question 3

What conditions must be met to open 4 kV non-vital AUX feeder bkr?

Close 4 kV AUX feeder bkr?

Answer 3

Open- switch to open

Close- synch switch to on

      - MOD full open or close
      - 25 kV ISO ground switch open
      - switch to close

Question 4

Describe how the “manual” automatic xfr to S/U and xfr to AUX work?

Answer 4

• synch switch on for xfr desired (going to S/U, switch is in S/U)
• interlocks made up (MOD, ground switch)
• synch check relay performs synch check

=> simultaneously closes one bkr and opens other

Question 5

What is danger of not matching flags?

Which flags have greater consequences of not matching?

Answer 5

If bkr trips on overcurrent, you will get no alarm

Aux bkr - If bkr trips on O.C. The lockout feature will not prevent an UNDESIRABLE xfr to S/U

Question 6

What 4 kV busses are power from what DG?

Answer 6

Bus F - DG 3
Bus G - DG 2
Bus H - DG 1

Question 7

What switches are used to manually xfr to S/U (12 and 4 kv)

What actions do you do if during xfr both bkrs remain closed

Answer 7

All xfr’s to and from S/U shall be done with manual xfr switches (using individual switches causes large circulating currents and damage)

Immediately Trip one of bkrs

Question 8

What differential overcurrent protection exists on 4 kV busses D and E if powered from S/U?

What is difference if buss powered from AUX?

Answer 8

• bus de-energized by;
  
  • tripping/ locking out S/u or aux feeder bkr
• load bkrs tripped
  
  • mcc xfmrs
  • station service xfmr
• diff protection light energized @ VB-5

AUX
- xfr to S/U is locked out

Question 9

What is main difference in differential overcurrent protection on the vital 4 kV busses versus the non-vital?

Answer 9

On vital buses, more automatic xfrs are locked out……for example if initially powered from:

Aux……..xfr to S/U and xfr to DG locked out

S/U…….xfr to DG locked out

Question 10

Bkr trips for vital 4 kV busses?
Aux
S/U
DG

Answer 10

Aux
   - O.C.
   - diff O.C.
   - 86 G1
   - 86 G11
S/u
   - O.C.
   - diff O.C.
DG
   - DG diff
   - bus diff
   - DG s/d relay
   - o.c. *
   - rev pwr *
   - DG loss of field*

• normally cutout because not seismically qualed