Main Power Distribution

Question 1

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)

Answer 1

One unit is required to be tripped within 4 minutes

Question 2

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?

Answer 2

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.

Question 3

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

Answer 3

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.

Question 4

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

Answer 4

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.

Question 5

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

Answer 5

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

Question 6

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

Answer 6

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.

Question 7

State the loads powered from A1 and B1 buses.

Answer 7

MFW pumps, RCPs

Question 8

State the non-safety related 4160V buses.

Answer 8

A2, B2

Question 9

State the safety related 4160V buses.

Answer 9

A3, B3, AB

Question 10

State the non-safety related 480V load centers.

Answer 10

A1, B1

Question 11

State the safety related 480V load centers.

Answer 11

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

Question 12

State the Unit 1 non-safety related MCCs.

Answer 12

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

Question 13

State the Unit 2 non-safety related MCCs.

Answer 13

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

Question 14

State the safety related MCCs.

Answer 14

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

Question 15

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

Answer 15

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

Question 16

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

Answer 16

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’

Question 17

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

Answer 17

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

Question 18

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

Answer 18

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

Question 19

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

Answer 19

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

Question 20

What supplies control power to 480V Load Centers?

Answer 20

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

Question 21

Describe Fast Dead Bus Transfer?

Answer 21

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.

Question 22

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

Answer 22

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

Question 23

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

Answer 23

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

Question 24

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

Answer 24

• 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

Question 25

Discuss Bus Differential Current Fault Relays.

Answer 25

* 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.

Question 26

Discuss Bus Ground Sensing Devices.

Answer 26

* 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

Question 27

Discuss Station Blackout X-Tie Breakers 4160V .

Answer 27

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.

Question 28

State Station Blackout X-Tie Breakers current limit.

Answer 28

550 amps (per procedure)

Question 29

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

Answer 29

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

Question 30

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

Answer 30

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

Question 31

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

Answer 31

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

Question 32

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

Answer 32

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

Question 33

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

Answer 33

NOT lit means Grounds are indicated

Question 34

What does a breaker cubicle amber light indicate?

Answer 34

Charging springs are charged and closing fuse is good.

Question 35

What does a breaker cubicle green light indicate?

Answer 35

Breaker is open and tripping power available.

Question 36

What does a breaker cubicle red light indicate?

Answer 36

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

Question 37

State the indications of SF6 low gas pressure.

Answer 37

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

Question 38

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

Answer 38

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

Question 39

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

Answer 39

Generator will trip.

Question 40

What is the maximum transformer gas concentration for safe approach?

Answer 40

200cc is MAX for safe approach.

Question 41

Describe Main Transformers.

Answer 41

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

Question 42

Describe Auxiliary Transformers.

Answer 42

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.

Question 43

Describe Startup Tranformers.

Answer 43

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

Question 44

Describe how to swap Aux/Startup Transformers.

Answer 44

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

Question 45

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

Answer 45

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

Question 46

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

Answer 46

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

Question 47

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

Answer 47

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

Question 48

Discuss Open Phase Detection System.

Answer 48

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.

Question 49

Discuss Potential Transformers.

Answer 49

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.

Question 50

Discuss Thermal Overloads.

Answer 50

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

Question 51

Discuss Normal/Isolate Switches

Answer 51

(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

Question 52

What are the potential power supplies to the SGBTF?

Answer 52

1B2 or 2A2 4160V