PB Class 4160VAC Flashcards
What is the purpose of the PB system?
Distributes electric power received off site or on site sources to safety related loads
What are the loads?
PBA-S03 - SP, HPSI, LPSI, CS, AF ‘N’, EW PUMP, ESSENTIAL CHILLER ‘A’, NORMAL CHILLER ‘A’ and LC’s 31,33,35
PBB-S04 - SP, HPSI, LPSI, CS, AF ‘B’, EW PUMP, ESSENTIAL CHILLER ‘B’, LCs 32,34,36
What is the normal flow path of PB system?
preferred from offsite source thru ESF xformers converting 13.8kv to 4160 class to PBA-PBB
Safety trains ‘A’ and ‘B’ are normally supplied by which load group?
PBA-S03 NBN-XO3
PBB-S04 NBN-XO4
How many trains of safety are required during modes 5 and 6?
1 required
Besides offsite power, what are other sources of electricity to PB system?
Diesel, SBOG or Flex DG
SBOG to ESF xformer NBN-X03 thru SO3AB breaker
What would a loss of 125vdc power system PK mean for PB system?
loss of control power so breakers would need to be manually operated
How does the BOP-ESFAS and PB systems interact?
PB receives signals from BOP-ESFAS system to energize fan and pump motors and reposition valves and dampers automatically in case of an emergency
What affect does a loss of power to the EW cooling pump motors have on the plant?
Will hamper the ability to remove core heat during shutdown cooling or accident conditions and renders the essential chiller for the affected train inoperable
How are the ESF transformers cooled?
non forced oil and forced air
ESF transformer protections?
Sudden pressure relay
Auto transfer relay
transformer differential
phase and ground overcurrent
What occurs when the sudden pressure relay is actuated?
Trips a lockout relay which then trips the transformers high side breaker and low side supply breakers
If SBOG is supplying the unit the NAN-S07 breaker would also trip
When racking out PB 4160 VAC breakers what precautions must be taken due to seismic concerns?
restrained or 2 inches off the ground
Why do some ‘B’ 4160VAC breakers have “remote/local and local” disconnect switches? What position should they be in?
Separate control power from the control room during a control room fire
left in remote/local
Where does control power come for for PBA-S03 and PBB-S04 come from?
PBA-S03 - PKA-D21
PBB-S04 - PKB-D22
All lockout relay on PBA AND PBB are capable of being reset remotely from the control room. How is this action performed?
Operator takes control switch to STOP, which energizes a reset solenoid.
What initiates the degraded voltage automatic feature in the PB system?
4 undervoltage relays will actuate when voltage drops below 90% rated voltage and remains there for about 30 seconds
what initiates the under voltage automatic feature in the PB system?
4 undervoltage relays will actuate when voltage drops below 75%
Where do the 8 undervoltage relays input into?
BOP ESFAS
When a degraded or undervoltage condition is sensed, BOP ESFAS will initiate what?
DG start
Load shed
Closure of DG breaker
Starts load sequencer (prevents overloading the DG)
What will trip the normal supply breaker in the PB system?
an electrical load shed generated from BOP-ESFAS
The alt supply breaker is closed from B01(prevents paralleling PBA-S03 AND PBB-S04)
A fault occurs on the associated ESF transformer
Electrical protective relays operate (86 lockout)
Concerning the alt supply breaker in the PB system, what would cause it to trip?
What effect does a loss of PB system have on the plant?
Will not immediately affect the plant but it is tech spec related and a unit shutdown will be required if power is not restored
Concerning loss of PB system what is the most limiting component in tech specs? how long will we have to restore the bus?
Battery chargers
2 hours
