12 kV Elec System

Question 1

What does the load tap changer do?

How much will one “tap” change voltage?

What is no load voltage maintained at?
What is the load voltage maintained at?

Answer 1

Controls voltage output of 12 kV SU bus by changing number of windings stepping down voltage from 230 kV

300 volts

129V on meter( both 12kv S/U feeder breakers open)
120v on meter(either 12kv S/U feeder to 12kv Bud D or E closed)

Question 2

What are loads off of 12 kV underground loop?

Answer 2

Temp air comp
SWRO
Met twr 
FW pmp house
Sim bldg 
Maint trng bldg
Admin bldg
Cold mach shop
Warehouse
Ionics
WHAT facility
Package boiler
B/U met twr

Question 3

Normal alignment operation?

Answer 3

12kv buses will be supplied by the Main Gen through Aux Transformer 1-1(2-1)

Question 4

12kv alignment for short term shutdown

Answer 4

In an event of a unit shutdown or trip, the 12kv buses are either manually or automatically shifted to the Startup Bus
-the SU Bus is normally energized by the 230kv switchyard through the OCB-212 and SU Transformer 1-1 (2-1)

Question 5

Longer term shutdown operation

Answer 5

during longer term shutdowns, as soon as practical following a shutdown, or when the 230kv power is not available, the 12kv system can be powered by backfeeding from the 500kv switchyard
-the main gen MOD is opened
- power is supplied from the switchyard through the generator output breakers 532(542) and/or 632(642)
-500kv stepped down to 25kv by the main transformer and then to 12kv by the aux transformer 1-1(2-1)

Question 6

SUT 1-1/1-2 protection

Answer 6

Trip switcher and 12kv S/U Bus Feeder Breaker on:
-phase overcurrent
-Differential
-sudden pressure

Question 7

SUT 1-1/2-1 backup protection

Answer 7

If fault still exists, trip open OVB-212 and other unit 12kv S/U bus feeder breaker

Question 8

What happens when the control handle is pulled out in manual?

Answer 8

S/U power is Inoperable

Question 9

What does the 12kv S/U bus feed?

Answer 9

-12kv Buses D and E
-Non-Vital 4kv Buses D and E
-Vital 4kv Buses F,G, and H
-Underground Distribution (Construction loop)

Question 10

12kv S/U Bus protection

Answer 10

-Bus under voltage(<70%)
->actuates ok 19-04
-Bus differential Current
->trips and locks out the affected S/U Bus
-> trips all 12kv Breakers
- Breaker overcurrent
-> trips breaker with fault

Question 11

Startup transformer 1-2(2-2) protection

Answer 11

Trips and lockouts 12kv and 4kv breakers on
-overcurrent
-sudden pressure
-Differential

Question 12

12kv Buses D and E bus protection

Answer 12

-Undervoltage(<68%)
-> trips CWPs and RCPs
-Differential
->trips supply breakers
-> prevents auto transfer to S/U bus by locking out S/U bus feeder breaker
->Trips CWPs and RCPs

Question 13

12kv Bus D and E reactor protection

Answer 13

-undervoltage (<68%)
-> Reactor trip > p-7 (1/2 sensors 2/2 buses)
-> TDAFWP Auto Start (1/2 sensors 2/2 buses)
-underfrequency (54hz)
-> Reactor trip > p-7 (2/3 sensors 1/2 buses)
-> Trip RCP breakers associated with the bus

Question 14

230kv circuit switchers purpose

Answer 14

Allows removal of SUT from service for maintenance without tripping the upstream breaker