Electric Power Xfr

Question 1

What does “bus auto xfr to S/U power cutout switch” do? Why have this feature? What busses posses this feature?

Answer 1

Blocks auto xfr from AUX -> S/U Controlled restoration from loss of power Degraded 230 kV system => disable one or more xfr’s All busses that have auto xfr capabilities 12 kV D, E 4 kV D, E, F, G, H

Question 2

What does the “bus auto xfr reset” push button do? What condition(s) must be met for the button to work? What busses does this button exist for?

Answer 2

Auto xfr relays reset and associated control functions cleared (also resets local reset device) The initiating condition must be cleared All busses with auto xfr capability

Question 3

What relays will “4 kV vital bus auto xfr trip relay reset device” reset? Can you manually take switch to Trip if it is in reset?

Answer 3

• Xfr to S/U
• Xfr to DG
• Sequencial loading
• Load shed

No, its like lockout relay, could break equip

Question 4

What are initiating events for an auto xfr to S/U for 4 kV system?

Include any differences between vital and non-vital

Answer 4

• Unit Trip (86G1 or G11)
• Both output bkrs open with:
  
  • Generator UV relay OR
  • MOD open
• Aux feeder bkr Trip
• **SI
• **4 kV bus UV

** vital bus only signals

Question 5

What are initiating events for an auto xfr to S/U for 12 kV system? (12 kv bus auto xft -> s/u relay)

Answer 5

• Unit Trip (86G1 or G11)
• Both output bkrs open with
  
  • Generator UV relay OR
  • MOD open
• Aux feeder bkr Trip

Question 6

What will block auto xfr to S/U?

12 kV

4 kV non vital

4 kV vital

Answer 6

• Aux feeder breaker tripped on O.C.
• Bus differential
• No voltage sensed on S/U feeder breaker
• *DG breaker closed
• *xfr to DG initiated
• *S/U feeder breaker tripped on O.C…..?

* only on vital 4 kV

Question 7

Describe actions for 12 kV auto xfr, include difference between fast and slow.

Answer 7

• synch check between aux and s/u (if good => fast, if not => slow)
• Trip aux bkr
• Trip CWP (if not cut out)
• close S/U bkr

* bus voltage decays < 25% before S/U bkr closes on slow transfer

Question 8

What is purpose for 12 kv bus UV relay (transfer trip relay)?

What actuates relay?

Answer 8

shed the RCP’s and CWP’s in event of:

• xfr -> s/u signal with 0 S/U power and/or
• UV condition on bus

actuation signals:

• 0 s/u volts and
• xfr -> s/u switch cut in (try to xfr) and
  
  • Unit trip or
  • aux bkr open or
  • PCB’s open with MOD open or Gen UV
• inst UV and
• time delay UV and
• UV relay cut-in (local)

Question 9

Describe purpose and actuation for 4 kv non vital bus UV relay

Describe purpose and actuation for 4 kv vital bus UV relay

Answer 9

Sheds loads on 4 kv bus on UV condition (CBP sets, #2HDP, Nash vac)

• requires 2/2 UV (inst and 4 sec)

sheds loads on 4 kv vital

sends xfr to DG relay

sends signal to close DG output (aft 2 sec time delay)

• 2/2 FLUR (inst and time delay, ~ 70% for 4 sec) OR
• 2/2 SLUR (inst with time delay, ~91% for 20 sec)

Question 10

Describe actions for 4 kv auto xfr to s/u, include difference between vital and non-vital.

Answer 10

aux feeder bkr opens

after either:

• bus voltage decays ~ 25% OR
• 4 seconds

S/U feeder bkr closes

* on vital bus sequencing timers start selected loads on bus