PB Class 4160VAC

Question 1

What is the purpose of the PB system?

Answer 1

Distributes electric power received off site or on site sources to safety related loads

Question 2

What are the loads?

Answer 2

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

Question 3

What is the normal flow path of PB system?

Answer 3

preferred from offsite source thru ESF xformers converting 13.8kv to 4160 class to PBA-PBB

Question 4

Safety trains ‘A’ and ‘B’ are normally supplied by which load group?

Answer 4

PBA-S03 NBN-XO3
PBB-S04 NBN-XO4

Question 5

How many trains of safety are required during modes 5 and 6?

Answer 5

1 required

Question 6

Besides offsite power, what are other sources of electricity to PB system?

Answer 6

Diesel, SBOG or Flex DG

SBOG to ESF xformer NBN-X03 thru SO3AB breaker

Question 7

What would a loss of 125vdc power system PK mean for PB system?

Answer 7

loss of control power so breakers would need to be manually operated

Question 8

How does the BOP-ESFAS and PB systems interact?

Answer 8

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

Question 9

What affect does a loss of power to the EW cooling pump motors have on the plant?

Answer 9

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

Question 10

How are the ESF transformers cooled?

Answer 10

non forced oil and forced air

Question 11

ESF transformer protections?

Answer 11

Sudden pressure relay
Auto transfer relay
transformer differential
phase and ground overcurrent

Question 12

What occurs when the sudden pressure relay is actuated?

Answer 12

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

Question 13

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

Answer 13

restrained or 2 inches off the ground

Question 14

Why do some ‘B’ 4160VAC breakers have “remote/local and local” disconnect switches? What position should they be in?

Answer 14

Separate control power from the control room during a control room fire

left in remote/local

Question 15

Where does control power come for for PBA-S03 and PBB-S04 come from?

Answer 15

PBA-S03 - PKA-D21
PBB-S04 - PKB-D22

Question 16

All lockout relay on PBA AND PBB are capable of being reset remotely from the control room. How is this action performed?

Answer 16

Operator takes control switch to STOP, which energizes a reset solenoid.

Question 17

What initiates the degraded voltage automatic feature in the PB system?

Answer 17

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

Question 18

what initiates the under voltage automatic feature in the PB system?

Answer 18

4 undervoltage relays will actuate when voltage drops below 75%

Question 19

Where do the 8 undervoltage relays input into?

Answer 19

BOP ESFAS

Question 20

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

Answer 20

DG start
Load shed
Closure of DG breaker
Starts load sequencer (prevents overloading the DG)

Question 21

What will trip the normal supply breaker in the PB system?

Answer 21

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)

Question 22

Concerning the alt supply breaker in the PB system, what would cause it to trip?

Question 22

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

Answer 22

Will not immediately affect the plant but it is tech spec related and a unit shutdown will be required if power is not restored

Question 23

Concerning loss of PB system what is the most limiting component in tech specs? how long will we have to restore the bus?

Answer 23

Battery chargers

2 hours

Question 24

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

Answer 24

DG is unavailable for use even on the opposite train bus