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Block 1 > Main Power Distribution > Flashcards

Main Power Distribution Flashcards

1
Q

Per 0-AOP-53.04 Reduced Offsite Transmission Capacity, what must be done if only one transmission line is available and BOTH units are online? (include time limit)

A

One unit is required to be tripped within 4 minutes

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2
Q

Per 0-AOP-53.04 Reduced Offsite Transmission Capacity, why must one unit be tripped within 4 minutes if only one transmission line is available?

A

Failure or delay in tripping the selected unit with two units on-line with one transmission line in service beyond the values specified in 0-AOP-53.04 Attachment 1, (4 minutes) may result in a LOOP and permanent damage to the transmission line.

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3
Q

What is min/max switchyard voltage with no SUTs in service?

A

Low limit - 230KV, High Limit - 244 KV

Low operability limit does not apply in Modes 5 & 6 because the unit load is minimal and a valid SIAS is not considered credible.

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4
Q

What is min/max switchyard voltage with SUTs in service?

A

Low limit - 230KV, High Limit - 241 KV

Low operability limit does not apply in Modes 5 & 6 because the unit load is minimal and a valid SIAS is not considered credible.

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5
Q

Per 0-AOP-53.02, Low SWYD Voltage, what actions are required with switchyard voltage <230KV?

A
  1. Both offsite sources (SUT’s) are declared inoperable
  2. Refer to T/S 3.8.1 for required actions – shutdown required if not corrected w/in 24 hours
  3. NRC notification required w/in 8 hours per LI-AA-102-1001, Regulatory Reporting
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6
Q

Per 0-AOP-53.03, High SWYD Voltage, what actions are required with switchyard voltage greater than limits?

A
  1. Ensure Main Generator is operating w/in the limits of the Generator Capability Curves
  2. Contact System to coordinate reducing VARS to lower switchyard voltage
  3. Monitor 6900V, 4160V and 480V bus voltages. Monitor for equipment damage.
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7
Q

State the loads powered from A1 and B1 buses.

A

MFW pumps, RCPs

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8
Q

State the non-safety related 4160V buses.

A

A2, B2

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9
Q

State the safety related 4160V buses.

A

A3, B3, AB

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10
Q

State the non-safety related 480V load centers.

A

A1, B1

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11
Q

State the safety related 480V load centers.

A

A2, B2 [A2, A5, B2, B5]

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12
Q

State the Unit 1 non-safety related MCCs.

A

A1, A2, A3, A4,
B1, B2, B3, B4, B10
B9 (SGBTF U1 feed)
1C

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13
Q

State the Unit 2 non-safety related MCCs.

A

A1, A2, A3, A10, A11,
B1, B2, B3, B10
B9 (SGBTF Unit 2 Feed)
2C

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14
Q

State the safety related MCCs.

A

A5, A6, A7, A8,
B5, B6, B7, B8,
AB

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15
Q

What supplies control power to 1A1 and 1B1 busses?

A

1A1 - 125V DC Bus ‘A’
1B1 - 125V DC Bus ‘B’

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16
Q

What supplies control power to 2A1 and 2B1 busses?

A

2A1 - 125V DC Bus ‘A’
2B1 - 125V DC Bus ‘B’

Note ** - SU XFMR Feeder Breakers to 6.9 KV Buses are opposite train powered
2A SUT feeder to 6.9 KV Bus 2A1 - 125V DC Bus ‘B’
2B SUT feeder to 6.9 KV Bus 2B1 - 125V DC Bus ‘A’

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17
Q

What supplies control power to 1[2]A2/B2 busses?

A

1[2]A2 - 125V DC Bus ‘A’
1[2]B2 - 125V DC Bus ‘B’

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18
Q

What supplies control power to 1[2]A3/1[2]B3 busses?

A

1[2]A3 - 125V DC Bus ‘A’
1[2]B3 - 125V DC Bus ‘B’

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19
Q

What supplies control power to 2A4/2B4 busses?

A

2A4 - 125V DC Bus ‘1C’ OR ‘2C’
2B4 - 125V DC Bus ‘1C’ OR ‘2C’

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20
Q

What supplies control power to 480V Load Centers?

A

All ‘A’ Train - 125V DC Bus ‘A’
All ‘B’ Train - 125V DC Bus ‘B’
1[2]AB - 125V DC Bus ‘AB’

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21
Q

Describe Fast Dead Bus Transfer?

A

On a plant trip, a primary and secondary lockout is generated, resulting in the switchyard east and mid breakers opening.
This requires control power to the switchyard breakers so they can open.
These lockouts initiate a power supply swap of the 6900V & 4160V buses from the Auxiliary Transformers to the Startup Transformers.
The Startup Transformer pick up load in such a quick time (usually ~ 3 cycles), that none of the loads trip.
If the bus transfer does not take place w/in 10 cycles (0.17 sec), then the fast dead bus transfer is locked out from occurring.
This results in an under-voltage condition on the A3 / B3 4160V buses.

22
Q

State the Unit 1 UV or DV Relay coincidence to cause an EDG auto start.

A

A3/B3 - 4160V Bus Relays:
* D/V – 2/2
* U/V – 2/2

A2/B2 - 480 V Relays
* D/V – 2/2 w SIAS / CIAS / MSIS
* NO U/V relays

23
Q

State the Unit 2 UV or DV Relay coincidence to cause an EDG auto start.

A

A3/B3 - 4160V Bus Relays:
* D/V – 2/3 w SIAS
* U/V – 2/2

A2/A5/B2/B5 - 480 V Relays
* D/V – 2/3
* U/V – 2/3

24
Q

What happens when UV or DV relays sense an UV or DV condition?

A
  • 3-2 & 2-3 tie breakers open
  • Loads shed – All breakers except Chg Pumps, BAM Pumps and CCW Pumps
    (Note: 1C Charging pump bkr opens and loads on 18 second load block)
  • EDG starts in isochronous / unity mode
  • EDG Output breaker close permissive (if no faults) once EDG at rated speed & voltage
  • Loads sequence on based on accident
25
Q

Discuss Bus Differential Current Fault Relays.

A
  • High Differential Current will actuate the “Lockout Relays” that will trip the Bus Supply Breakers.
  • Breakers cannot be closed until the problem is resolved and the Lockout Relays are reset.
  • Resetting is done locally at the bus. Blue light will flash if lockout has actuated.
  • Found on the A1/B1, A2/B2, A3/B3, A4/B4, & 1AB/2AB buses.
26
Q

Discuss Bus Ground Sensing Devices.

A
  • 50G relay used for ground detection. Senses differential current across all three phases
  • Grounds are indicated by the ground white light going out on the breaker cubicle
  • Grounds generally result in all breakers closest to the ground to trip open, and lockout. Requires resetting the 86 lock-out device before breakers can be reclosed
27
Q

Discuss Station Blackout X-Tie Breakers 4160V .

A

Both units have 3 position key switches - Trip/Normal/Close
* Connect 4160V buses 1AB and 2AB. Used to supply power to opposite unit in the event of SBO.
* 72 hour admin limit to restore inoperable breaker per ADM-11.1 & ADM-17.16
* One EDG is capable of supplying emergency power for safe shutdown to both Units
Max 550 amps due to A3/B3 to AB bus connection.
* Upper lights – Red and Green for other Unit’s breaker
* Lower lights – Red, Amber, Green for that Unit’s breaker
* Breakers are interlocked such that the Unit in SBO closes their breaker first – Ex: U1 is in SBO, then 1AB X-tie is closed 1st, to allow 2AB X-tie to be closed.

28
Q

State Station Blackout X-Tie Breakers current limit.

A

550 amps (per procedure)

29
Q

Pertaining to Station Blackout X-Tie Breakers, what is the weakest link?

A

Weak link in system is the AB 4.16 kV tie to A3 or B3 4.16 kV bus cabling.
Cables rated at 600 amps for 100 hours continuous use, but limited to 550 amps in procedure for a safety margin. (Instrument errors, etc.)
This limit is for running currents; short time starting amps ok to go above 550, up to 745 amps. Use supplying unit’s amp meter for limit.
The supplying unit AB ammeter will show all current sent to the other unit and any loads on the supplying units AB bus, while the receiving unit AB ammeter will only show current sent to the receiving units A3 or B3 bus, not the current used for any loads on the other units AB bus.

Example: Unit 1 is the unit in SBO. Assuming no Unit 2 loads on the EDG used for cross-tie. Unit 1 has 300 amps on its A3 bus which is tied to its AB bus and has 100 amps going to the 1C CCW pump from the Unit 1 AB bus. The Unit 2 AB ammeter will read 400 amps while the Unit 1 AB ammeter will read 300 amps. If the supplying unit has loads on its AB bus, this takes away from the 550 amps available for the receiving unit

30
Q

Discuss X-Tie Breakers for 4160V AB Buses and 480V AB Load Centers.

A

Unit 1 - Has plain hand switches
Unit 2 - Key Lock switches

Breakers are Electrically Interlocked thru RTGB switches to prevent simultaneous closure
Inside breakers open on undervoltage, requiring a specific sequence when swapping AB bus supplies from one train to the other - (Inside bkr opened, Outside bkr opened, Outside bkr closed, Inside bkr closed)
Dead Bus Transfer when swapping AB Bus power sources

31
Q

Discuss MCC 1C (MCC 2C) Automatic Transfer.

A

Connected to normal 480 V Load Center 1A1 & 1B1 through an ABT
Normal Seeking ABT - Transfers to alternate on loss of power, then when the normally selected bus regains power, ABT transfers back

32
Q

Discuss Normal 480V LC 1A1 & 1B1 (2A1 & 2B1) X-Tie.

A

Interlocked such that at least one of the LC A1 or B1 supply breakers must be open to allow x-tie breaker closure
480V LC supply breakers open on U/V if 4160V XFMR feeders breakers are open

33
Q

What is the condition of the Ground Detection Lights on a breaker cubicle if a ground is detected?

A

NOT lit means Grounds are indicated

34
Q

What does a breaker cubicle amber light indicate?

A

Charging springs are charged and closing fuse is good.

35
Q

What does a breaker cubicle green light indicate?

A

Breaker is open and tripping power available.

36
Q

What does a breaker cubicle red light indicate?

A

Tripping circuit has power, continuity exists through trip coil, and breaker is closed.

37
Q

State the indications of SF6 low gas pressure.

A

Low Gas Pressure alarm (34.3 psig)
Amber light on door - OFF
Breaker failure alarm in control room (RTGB)

38
Q

State the indications of SF6 breaker low-low gas pressure.

A

Low – Low Gas Pressure (28.6 psig)
Amber light on breaker - OFF

39
Q

State the consequence of opening a potential transformer compartment door with the generator on line.

A

Generator will trip.

40
Q

What is the maximum transformer gas concentration for safe approach?

A

200cc is MAX for safe approach.

41
Q

Describe Main Transformers.

A

Main Transformers (2) - Step up power from 22KV to 230 KV.
* Forced oil & air cooling [oil directed, air forced]. Alternate & Lead Group selector switches. All components stop on Deluge activation
* Delta Current and Ground Current Relays cause Bus Lockout, & trips Main Generator Primary and Secondary lockout relays.
* Gas Detector – Mounted on XFMR. 200 cc is MAX for safe approach
* Serveron Gas Monitor – Analyzes for gases caused by insulation breakdown

42
Q

Describe Auxiliary Transformers.

A

Auxiliary Transformers - Step down power from 22 KV to 6900V and 4160V.
* Differential current relay actuation will actuate a main generator trip via the primary generator lockout relay located on the back of the RTGB.
* Fault pressure relay actuation will actuate a main generator trip via the secondary generator lockout relay located on the back of the RTGB.

43
Q

Describe Startup Tranformers.

A

Startup Transformer (SUT) - Step down power from 230 KV to 6900V and 4160V when Main Generator not on-line.
* Bus Lockout from Diff Current and Fault Pressure trips primary and secondary breakers to Startup Transformers. There is no turbine trip from this.
* Ground Overcurrent trips primary side bkrs, Phase Overcurrent trips secondary side bkrs.
* If a SUT is not available the Units can be cross connected to supply power from the other Unit’s SUT by physically removing the unavailable SUT breaker from its cubicle and installing it in the Bus X-Tie Cubicle
* Control the number of breakers (2 bkrs for 3 bkr cubicles) to prevent cross-tying SUT’s

44
Q

Describe how to swap Aux/Startup Transformers.

A
  1. SUTs placed in-service ~30% during down-power, Removed from service ~20% during up-power
  2. Aux Transformers placed in-service ~20% during up-power, Removed from service ~30% during down-power
  3. Swap performed by:
    a. Place sync plug in position aligning with XFMR to be placed in-service.
    Expect Incoming and Running voltage to be ~ matched.
    b. Close desired XFMR supply breaker & verify breaker closes
    c. Slowly release the switch and verify off-going XFMR breaker opens
    d. Restore sync plug to OFF
45
Q

What are the actions if an Aux Transformer is on fire?

A

Per 1(2)-AOP-53.02, Aux Transformer, remove XFMR from service per ATT 1

46
Q

What are the actions if a Main Transformer is on fire?

A

Per 1(2)-AOP-53.03, Main Transformer, Trip RX (if Main Generator breakers are closed)

47
Q

What are the actions if a Startup Transformer is on fire?

A

Per 1(2)-AOP-53.04, Startup Transformer, Isolate XFMR per Att 2

48
Q

Discuss Open Phase Detection System.

A

Utilizes a 2/3 logic to detect an open condition on any SUT phase. Intended use was to generate a Transformer lockout if detected. Currently the plant decision is to make this an alarm only feature.

49
Q

Discuss Potential Transformers.

A

Potential Transformers
* Used primarily for measuring voltage for metering indication and Relay purposes. However a blown fuse can result in a Unit trip, making the plant think that a bus is dead.
* If the compartment doors are opened with the generator on-line the generator will trip.
* A mechanical linkage disconnects the fuses when the door is opened and is automatically grounded.
* The Main generator potential fuses are located on the mezzanine level of the turbine building just behind the west side of the isophase bus duct coolers.
* The 6.9 kV and 4.16 kV potential fuses are located on top of their respective breakers in the turbine switch gear room.

50
Q

Discuss Thermal Overloads.

A

Thermal Overload Bypass Switch: Normal/Bypass or Maint/Test
Normally is kept in the Normal/Bypass position so that tripping by Thermal Overload is disabled [required by TS on Unit 2], Indicating Lights are still on even after trip. T/S 3.8.4 applies when switches are placed in Maintenance/Test

51
Q

Discuss Normal/Isolate Switches

A

(Appendix “R” Required)
* These switches cut out the wiring and control switches in the Control Room
* Normal - the Control room switches are active but the local switches are still in the circuit too
* Isolate - the only control is local at the breaker with the switch on the breaker cubicle door
* Causes an alarm in the Control room for the Appendix “R” related equipment

52
Q

What are the potential power supplies to the SGBTF?

A

1B2 or 2A2 4160V

Block 1 (4 decks)

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