Class 120 V Instrument

Question 1

Is the PN system grounded or ungrounded?

Answer 1

Ungrounded.

Question 2

(ANNUNCIATOR)
120VAC IE
PNL D27
INV C
TRBL

Answer 2

Annunciator indicates either a loss or possibly impending loss of a distribution panel due to:

• Inverter overvoltage, UV, DC UV, overcurrent or other inverter troubles such as fan failures.
• Distribution panel problems include UV, ground or stdby supply NOT available.

Question 3

List all the PN distribution panels and their respective normal power supplies.

Answer 3

PNA-D25 powered from PKA-M41
PNB-D26 powered from PKB-M42
PNC-D27 powered from PKC-M43
PND-D28 powered from PKD-M44

Question 4

Describe the normal and alternate power supplies for PN.

Answer 4

Normal supply is from PK through an inverter, alternate is from PH from a voltage regulator.

Question 5

What are the conditions required under LCO 3.8.7 that allows one PN inverter to be removed from service for 24 hours?

Answer 5

1) The associated AC vital instrument bus is energized from its Class 1E constant voltage source regulator.
2) All other vital instrument AC buses are energized from their associated OPERABLE inverters.

Question 6

List the alternate power supply, including it’s respective Voltage Regulator, for each PN distribution panel.

Answer 6

PHA-M35 -> PNA-V25 -> PNA-D25
PHB-M36 -> PNB-V26 -> PNB-D26
PHA-M31 -> PNC-V27 -> PNC-D27
PHB-M32 -> PND-V28 -> PND-D28

Question 7

(ANNUNCIATOR)
120VAC IE
PNL D25
INV A
TRBL

Answer 7

Annunciator indicates either a loss or possibly impending loss of a distribution panel due to:

• Inverter overvoltage, UV, DC UV, overcurrent or other inverter troubles such as fan failures.
• Distribution panel problems include UV, ground or stdby supply NOT available.

Question 8

Fill in the respective train designation for each PN inverter and PK power supply; and then match each PN inverter with its respective power supply:

PN _ -N11 PK _ -M43
PN _ -N14 PK _ -M41
PN _ -N12 PK _ -M44
PN _ -N13 PK _ -M42

Answer 8

PNA-N11 –> PKA-M41
PNB-N12 –> PKB-M42
PNC-N13 –> PKC-M43
PND-N14 –> PKD-M44

Question 9

You are in U2, when it is announced that PND-N14 has been lost due to an Inverter lock-up. What action if any is required to restore power to the PN ‘D’ distribution panel?

Answer 9

None
In Units 2 & 3 on a loss of normal power, a Static Transfer Switch located adjacent to the inverter, will automatically transfer the distribution panel to the voltage regulator without interruption.

When power returns, the static transfer switch does NOT transfer back automatically.

Question 10

(ANNUNCIATOR)
120VAC IE
PNL D26
INV B
TRBL

Answer 10

Annunciator indicates either a loss or possibly impending loss of a distribution panel due to:

• Inverter overvoltage, UV, DC UV, overcurrent or other inverter troubles such as fan failures.
• Distribution panel problems include UV, ground or stdby supply NOT available.

Question 11

What does each position of the “Bypass Disconnect Switch” do in Units 2 & 3 Class 1E inverters?

(Hint: The positions are ‘BYPASS’, ‘OFF’, and ‘STATIC’)

Answer 11

BYPASS - Connects the distribution panel directly to the voltage regulator
OFF - Disconnects the distribution panel from both power supplies
STATIC - Aligns the distribution panel to the Static Switch

Note: In Units 2&3, if the PN bus is transferred to the voltage regulator using the ‘Bypass’ switch, a loss of the PN bus will occur when going through the ‘OFF’ position.

Question 12

In U3, you have been directed by the CR to manually transfer PNB-D26 to the alternate power supply (voltage regulator). Given the choice of 2 buttons, “FORWARD TRANSFER SWITCH” or “REVERSE TRANSFER SWITCH”, which do you choose?

Answer 12

REVERSE TRANSFER SWITCH

Aligns to the voltage regulator

Question 13

List some causes for the U2 & U3 Static Transfer Switches to automatically transfer to the voltage regulator.

Answer 13

Inverter lock-up
Inverter power fuse blows
DC Input Voltage Low (105 VDC)
Inverter Output Current High (229-234 amps)
Inverter Logic 25 Volt Supply Low
Over temperature on an Inverter heat sink
AC Output Voltage High (127 VAC)
AC Output Voltage Low (113 VAC)
Inverter Output Bkr Tripped

Question 14

(ANNUNCIATOR)
120VAC IE
PNL D28
INV D
TRBL

Answer 14

Annunciator indicates either a loss or possibly impending loss of a distribution panel due to:

• Inverter overvoltage, UV, DC UV, overcurrent or other inverter troubles such as fan failures.
• Distribution panel problems include UV, ground or stdby supply NOT available.