Class 4.16 kV (PB)

Question 1

What is the purpose of the PB system?

Answer 1

Distributes electrical power received from off-site or on-site sources to safety related loads

Question 2

What is the normal flowpath of the PB system?

Answer 2

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

Question 3

Safety train ‘A’ and ‘B’ are normally supplied by which load groups?

Answer 3

Safety train ‘A’: load group 1 (PBA-SO3) from NBN-X03

Safety train ‘B’: load group 2 (PBA-SO4) from NBN-X04

Question 4

How many trains are required during mode 5 and 6?

Answer 4

Both may be used, but only one is required.

Question 5

Besides off-site power, what are my other sources of electricity for the PB system?

Answer 5

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

Question 6

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?

Answer 6

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.

Question 7

How would a loss of the Class 125 VDC power system(PK) affect PB system?

Answer 7

Loss of control power, which means breakers can only be operated manually

Question 8

How does the BOP-ESFAS and PB systems interact?

Answer 8

PB receives signals from BOP-EFAS system to energize fan and pump motors and reposition valves and dampers automatically in case of an emergency

Question 9

Loads supplied by PB system

Answer 9

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)

Question 10

What affect does a loss of power to the Essential Cooling Water pump motors have on the plant?

Answer 10

Will hamper the ability to remove core heat during shutdown cooling or accident conditions and renders the essential chillers for the affected train inoperable

Question 11

How are the ESF Service Transformers cooled?

Answer 11

Combination of Oil and Air and forced air cooling

Question 12

Name the four ESF Service Transformer Protections

Answer 12

Sudden Pressure Relay(SPR)
Automatic Transfer Relay
Transformer Differential
Phase and Ground Overcurrent

Question 13

How are the PB switchgears physically situated in the Control Building as outlined by Tech Specs?

Answer 13

Located in separate rooms of the seismic category one Control Building

Question 14

How are the PB switchgear breakers normally operated?

Answer 14

Normally opened or closed remotely, from either the control room or by inputs from automatic control devices

Question 15

When racking out 4160 VAC breakers, what precautions must be taken due to seismic concerns?

Answer 15

They must be either raised 2 inches from the floor or restrained using proper tie downs.

Question 16

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?

Answer 16

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.

Question 17

Concerning PBA-S03 and PBB-S04 circuit breakers, where does the control power come from?

Answer 17

PBA-S03 receives from PKA-D21

PBB-S04 receives from PKB-D22

Question 18

All lockout relays on PBA-S03 and PBB-S04 are capable of being reset remotely from the control room. How is this action performed?

Answer 18

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

Question 19

What initiates the Degraded Voltage automatic feature in the PB system?

Answer 19

Four undervoltage relays will actuate when voltage drops below 90% rated voltage and remains there for about 30 seconds

Question 20

What initiates the Degraded Voltage automatic feature in the PB system?

Answer 20

Four undervoltage relays will actuate when voltage drops below 90% rated voltage and remains there for about 30 seconds

Question 21

When a degraded or undervoltage condition is sensed, BOP ESFAS will initiate what?

Answer 21

Diesel generator start
Load shed
Closure of Diesel Generator Breaker
Starts load sequencer(prevents overloading the DG)

Question 22

Concerning the Normal Supply Breaker in the PB system, what would cause it to trip?

Answer 22

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)

Question 23

Concerning the Alternate Supply Breaker in the PB system, what would cause it to trip?

Answer 23

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)

Question 24

What effect does a loss of PB system have on the plant?

Answer 24

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.

Question 25

Concerning a loss of PB system, what is the most limiting component in Tech Specs? How long will we have to restore the bus?

Answer 25

Battery Chargers

Two hours

Question 26

How is the Diesel Generator affected by the unavailability of its respective 4160 VAC bus?

Answer 26

DG is unavailable for use, even on the opposite train bus