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Systems > Aux Power > Flashcards

Aux Power Flashcards

1
Q

Aux Power Purpose

A

Supply Electrical power to Plant Equipment under all Conditions

  • Offsite Power from the Switchyards
  • Alternate AC from SBO
  • Onsite Power from transformers, 4kV/480vAC, Low Voltage AC and DC Systems
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2
Q

What is Divisional Separation?

A

The electrical loads for each unit i splite between two systems. The plant layout provides physical separation of qualified circuits and redundant loads are split between the divisions.

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3
Q

What is a Qualified Circuit?

A

Consists of all breakers, transformers, switches, interrupting devices, cabling, and controls required to transmit power from the offsite transmission network to the onsite Class 1E ESS bus.

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4
Q

What are the Engineered Safety Features?

A

UFSAR Section 6:

  • Containment
  • Control rod Velocity Limiter
  • Control Rod Housing Support
  • Containment Atmosphere Control
  • Standby Coolant Supply
  • Emergency Core Cooling System
  • Main Steam Line Flow Restrictors
  • Isolation Condenser
  • SBLC
  • Reactor Protection System
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5
Q

What are the breakers off TR21 (to buses) called?

A

MAIN FEED BREAKERS

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6
Q

What are the Breakers (to buses) off TR22 called?

A

Reserve Feed Breakers

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7
Q

What are the ESS Buses?

A

23,23-1, 28, 24, 24-1, 29

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8
Q

What conditions must be met for a fast bus transfer from RAT to UAT (Vice Versa)?

A

1) Tripped breaker contract switch in normal after closed (NAC)
2) No lockout on breaker that should auto close on
3) Breaker that tripped must actually open
4) RAT/UAT must be available

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9
Q

How do you determine if TR21 is available?

A

1) Main power disconnects closed AND

2) At least one of two main generator output breakers closed.

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10
Q

What logic (emergency) prevents 2/3 EDG closing on 4kV-1 bus?

A

Don’t Close on ME if ECCS on THEE

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11
Q

What are the main and reserve control power sources for Bus 21?

A

Main : 2A-2;

Reserve 2B-2

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12
Q

What are the main and reserve control power sources for Bus 22?

A

Main: 2B-2; Reserve: 2A-2

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13
Q

What are the main and reserve control power sources for Bus 23?

A

Main: 2A-1; Reserve: 2B-1

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14
Q

What are the main and reserve control power sources for Bus 24?

A

Main: 2B-1; Reserve: 2A-1

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15
Q

What are the main and reserve control power sources for Bus 23-1?

A

Main: RB Dist. Panel; Reserve: 2B-1

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16
Q

What are the main and reserve control power sources for Bus 28?

A

Main: RB Dist. Panel; Reserve: 2B-1

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17
Q

What are the main and reserve control power sources for Bus 24-1?

A

Main: 2B-1; Reserve: RB Dist Panel

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18
Q

What are the main and reserve control power sources for Bus 29?

A

Main: 2B-1; Reserve: RB Dist Panel

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19
Q

What are the main and reserve control power sources for Bus 25?

A

Main: 2A-2; Reserve: 2B-2

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20
Q

What are the main and reserve control power sources for Bus 26?

A

Main: 2B-2; Reserve: 2A-2

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21
Q

What are the main and reserve control power sources for Bus 27?

A

Main: 2B-2; Reserve: 2A-2=

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22
Q

If there is a loss of high side power (undervoltage) to TR-22, what will be power source to Bus 22 and 24?

A

None. ONLY A LOSS OF POWER TO TR-22 will not cause 4-kV breakers to trip and consequently will not cause fast transfer.

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23
Q

What are the main and reserve control power for Bus 20?

A

Main 2B-2; No Reserve

24
Q

What normally supplies the feed power to TR 22?

A

138kV via TR86 from 345kV Bus 3. Alt is 138kV Bus 1 (unqualified)

25
Q

What are the trip and lockout signals for the UAT and RAT?

A

Sudden Pressure
Differential Current
Neutral Overcurrent

26
Q

What breakers will open following trip of RAT?

A

U2 (TR22 trip) - Breakers feeding 4kV buses; TR86 (or 138kV) breakers to isolate feed bus.
U3 (TR32 Trip) - (Fed from Bus 8) - trips breakers 4-8, 8-9, and 8-15 to isolate load.

27
Q 
Dash Busses:
Numbers?
Locations?
Primary Loads?
Feeds?
A

23-1, 24-1
RB 545
Primarily feed ECCS systems
Fed by TR 21 and 22 (normally; can be fed by other as alternate)

28
Q

What is the logic for the 4kV-1 feed breakers?

A

2 breakers between 4kV and 4kV-1 buses (feed breaker and Main feed breaker):
MFB is slaved to the FB on closing: MFB waits for FB to close and will open anytime FB opens.

29
Q

What happens if 4kV-1 main feed breaker opens on own transient?

A

Feed breaker opens on undervoltage and causes EDG autostart.

30
Q

What is the logic between 4kV/4kV-1 feed breakers and Main Feed Breakers and the EDG Auto-start?

A 
Main Feed (4kV-1)- tied to EDG auto Start - when breaker opens on trip, EDG autostart.
Feed - (4kV) - EDG output breaker auto-closure tied to them.
31
Q

Where do the Unit Aux cross-ties connect and are there any limitations?

A

At the 4kV-1 buses from other unit. Both cross-ties cannot be connected simultaneously (admin) if source unit is on single aux transformer.

32
Q

What are the associated 480V Buses and their divisions?

A

Div I: 25, 28(ESS)

Div II: 20, 26, 27, 29(ESS)

33
Q

What operational tie for 480V bus low and high side breakers?

A

Low side slaved to high side. High side closes and opens first.

34
Q

What protection is available to the 480V Bus Breakers?

A

High side has overcurrent device.

Low side has RMS-9 Device Overload Device.

35
Q

What is an RMS-9 device?

A

It is an overload device that does not require 125vDC control power. It is independent from breaker control power and uses line current to control.

36
Q

What are the 4kV Interlock protections?

A 
4kV-1 Degraded Voltage
4kV Bus Undervoltage
4kV-1 Bus Undervoltage
4kV Bus Fast Transfer
Automatic Transfer Interlock Relay
Reserve Feed Undervoltage Relay
37
Q

What is the logic and setpoints for 4kV-1 degraded voltage protection?

A
  • Set at 93% of 4160v; reset at 3893v (SECOND LEVEL UV)
  • Rated voltage less than 93% for 7 seconds, MCR alarm and 5 min timer starts
    - Auto reset on condition clear prior to 5 minutes
  • 5 min. timer times out - First Level UV relays actuate
  • **IF ECCS SIGNAL INITIATION DURING 5 minutes - first level UV relays actuated. Degraded voltage logic bypassed and EDG closed onto bus.
38
Q

What is logic and setpoint for 4kV Bus undervoltage protection?

A

Setpoint - 70% rated voltage; auto reset at 93%

Upon initiation - 4kV-1 feed breakers also trip so EDG only picks up 4kV-1 bus

4kV bus UV relays also send autostart signal to EDG, but EDG breaker WILL NOT CLOSE unless feed breaker at 4kV buses open.

39
Q

4kV-1 Bus Undervoltage logic and setpoint?

A

Set - 70% rated voltage will actuate load shedding (first level relays) - Resets at 93% rated

All loads will shed except 480V ESS Buses, 2A/B RBCCW Pps and Main feed breaker on 4kV-1 bus (ECCS loads shed off and require manual reload)
All feed breakers except EDG output trip open.
Auto start signal to Division EDG.

40
Q

What is the Auto Transfer Interlock Relay?

A

Prevents automatic power transfer from RAT to UAT when UAT not available.

Cannot close MFB to 4kV bus from UAT unless main power transfer disconnects are closed and at least one main generator output CB is closed.
UAT is available: MPT disconnects closed; 1of2 gen. output breakers closed (ESSENTIALLY UNIT IS ONLY AND TIED TO GRID.

41
Q

What is Reserve Feed Undervoltage Relay Function?

A

Interlock that prevents closing 4kV bus Reserve Feed Breaker onto RAT if RAT secondary side goes undervoltage.

42
Q

What does the UV Relay on Bus 22 and 24 do in terms of the RAT?

A

Locks out the Reserve Feed Breaker for Bus 21/22 and Bus 23/24 respectively. Must be reset manually.

43
Q

How does the 4kv-1 Bus Tie interlock function?

A

Trip and block applied to both unit tie breakers upon differential current. (on U2 4kv-1 feed breakers)

Div I - interlock prevents tie breaker only on U2 from being closed if 2/3 EDG is closed onto either 23-1 or 33-1

Div II - U2 tie breker is tripped and blocked if both unit EDG output breakers are closed to prevent EDG paralleling.

44
Q

What is the purpose of Bus Tie Differential Current Protection?

A

Differential Current indicates a fault on the tie line by comparing current entering a cable with current leaving cable.
Trip and Block sent to both FB on 4kV and MFB on 4kv-1

45
Q

What interlocks occur on a 4kV bus Overcurrent?

A

If occurs on either MFB or RFB, trip and lockout signal sent to both breakers. MFB and RFB lockout devices on Bus 23 and 24 also trip and lockout feed breaker to 4kv-1 buses.
Feed from SBO lockedout.
Must be manually reset.

46
Q

Where are the 4kV Bus Overcurrent Resets?

A

Bus 21/22 - at Bus 22
Bus 23/24 at Bus 24
Bus 31/32 at Bus 31
Bus 33/34 at Bus 34

47
Q

What trips on 480V Bus UV( Non-ESS)?

A

UV Relay actuates - UV sends trip to 4kV feed breaker on supplying bus.
Resets automatically when bus re-energized

48
Q

480V Load Shedding for ESS Buses (NON ECCS)?

A 
Impacts Buses 28 & 29 (38 & 39):
DW Coolers do not trip
Loads tripped(shed) and locked out until reset (902-8 or locally):
FPC Pumps
RB Vent Fans
RB Exhaust Fan
S. TB Vent Fan
RWCU Aux Pp (28/38)
MCC 29-3, 29-5, 29-6, 29-8 (29)
49
Q

480V ECCS Load Shed (ESS Bus)?

A

ECCS Load shed uses Core Spray Logic and is independent from bus voltage:
S. TB Vent Fans
DW Coolers (U8 - A, B, F, G; U9 - C, D, E)
MCC U9-5, -6

LOADS CANNOT BE RESET WITHOU ECCS CLEAR or JUMPERED

50
Q

What is the 25 to 26/27 Crosstie logic?

A

25 can only be fed from 26 automatically, 27 manually.
25 will feed either 26 or 27 BUT NOT BOTH; Typically whichever receives signal first.
Once auto transfer occurs, but be reset manually.
Auto transfer is DUMB - will attempt even if bus tripped on overcurrent.

51
Q

How are Buses 28-7 and 29-7 normally lined up?

A

MCC 28-7 and 29-7 hard wired together; normally powered from Bus 29.

52
Q

What happens to MCC 28-7 and 29-7 upon loss of Bus 29?

A

Contact opens on 29-7 and starts 17 second timer.
Provides time for EDG to start, and close on 24-1.
If no power within 17 seconds, 29-7 feed breaker opens and 28-7 feed breaker closes (even if Bus 28 dead)
** Bus 29 feed also trips on unstable voltage/frequency**

53
Q

If Bus 28 is supplying MCC 28-7/29-7 and trips, what happens?

A

MCC 28-7 and 29-7 stay dead if does not repower - no auto transfer to Bus 29.

54
Q

How do you transfer MCC 28-7/29-7 back to Bus 29 if being powered by 28?

A

Hold Bus 28 Control in trip then close Bus 29 feed. Otherwise Bus 28 feed breaker will try to autoclose.

55
Q

TB 480V Overcurrent - What logic prevents auto cross tie operation?

A

4kV feed and main feed breakers trip open.

cross tie breakers will close and then trip open if fault still exists.

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