Class 4.16 kV (PB) Flashcards
What is the purpose of the PB system?
Distributes electrical power received from off-site or on-site sources to safety related loads
What is the normal flowpath of the PB system?
Electrical power from the preferred off-site power source through the ESF transformers, converting Non-class 13.8kV to 4160 V Class power and distributes to PBA-S03 and PBB-S04
Safety train ‘A’ and ‘B’ are normally supplied by which load groups?
Safety train ‘A’: load group 1 (PBA-SO3) from NBN-X03
Safety train ‘B’: load group 2 (PBA-SO4) from NBN-X04
How many trains are required during mode 5 and 6?
Both may be used, but only one is required.
Besides off-site power, what are my other sources of electricity for the PB system?
Standby power from Diesel Generators PEA-G01 for ‘A’ safety train bus and PEB-G02 for ‘B’ Safety train bus.
Station black out generator to ESF transformer NBN-X03 through breaker NAN-S03AB
As far as the Units are concerned, where can the SBOG’s supply emergency power to?
Why can’t the SBOG’s supply emergency power to Units 2 and 3 simultaneously?
To any one unit, units 1 and 2 or units 1 and 3 simultaneously
Due to the length of the cable run from WRF and the time for the protective relaying to take effect.
How would a loss of the Class 125 VDC power system(PK) affect PB system?
Loss of control power, which means breakers can only be operated manually
How does the BOP-ESFAS and PB systems interact?
PB receives signals from BOP-EFAS system to energize fan and pump motors and reposition valves and dampers automatically in case of an emergency
Loads supplied by PB system
Safety Injection and Shutdown cooling pump motors Essential Spray Pond pump motors Essential Cooling Water pump motors Aux Feed Pump motors ‘A’ Normal Chiller Essential Chillers PG load centers (480V)
What affect does a loss of power to the Essential Cooling Water pump motors have on the plant?
Will hamper the ability to remove core heat during shutdown cooling or accident conditions and renders the essential chillers for the affected train inoperable
How are the ESF Service Transformers cooled?
Combination of Oil and Air and forced air cooling
Name the four ESF Service Transformer Protections
Sudden Pressure Relay(SPR)
Automatic Transfer Relay
Transformer Differential
Phase and Ground Overcurrent
How are the PB switchgears physically situated in the Control Building as outlined by Tech Specs?
Located in separate rooms of the seismic category one Control Building
How are the PB switchgear breakers normally operated?
Normally opened or closed remotely, from either the control room or by inputs from automatic control devices
When racking out 4160 VAC breakers, what precautions must be taken due to seismic concerns?
They must be either raised 2 inches from the floor or restrained using proper tie downs.
Why do some 4160VAC breakers on the ‘B’ train bus have a “Remote/Local and Local” disconnect switches? What position should these switches normally be in?
Separates the control circuit of the breaker from the control room in the event of a fire. These should always be in the “Remote and local” position, not “local” to allow the control room operation.
Concerning PBA-S03 and PBB-S04 circuit breakers, where does the control power come from?
PBA-S03 receives from PKA-D21
PBB-S04 receives from PKB-D22
All lockout relays on PBA-S03 and PBB-S04 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. This operation must be carefully controlled, as additional damage will surely result if it is reset and energizes a faulted motor
What initiates the Degraded Voltage automatic feature in the PB system?
Four undervoltage relays will actuate when voltage drops below 90% rated voltage and remains there for about 30 seconds
What initiates the Degraded Voltage automatic feature in the PB system?
Four undervoltage relays will actuate when voltage drops below 90% rated voltage and remains there for about 30 seconds
When a degraded or undervoltage condition is sensed, BOP ESFAS will initiate what?
Diesel generator start
Load shed
Closure of Diesel Generator Breaker
Starts load sequencer(prevents overloading the DG)
Concerning the Normal Supply Breaker in the PB system, what would cause it to trip?
An electrical load shed is generated from the BOP-ESFAS system
The alternate 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 Alternate Supply Breaker in the PB system, what would cause it to trip?
An electrical load shed is generated from the BOP-ESFAS system
The normal system supply breaker is closed from B01
A fault occurs on the associated ESF Transformer
Electrical protective relays operate(86 Lockout)
What effect does a loss of PB system have on the plant?
Will not immediately affect the plant, but since it is a Tech Spec related system, a unit shutdown will be required if power is not restored.
Concerning a loss of PB system, what is the most limiting component in Tech Specs? How long will we have to restore the bus?
Battery Chargers
Two hours
How is the Diesel Generator affected by the unavailability of its respective 4160 VAC bus?
DG is unavailable for use, even on the opposite train bus
