13.8KV Normal Auxiliary Power System(EPM)

Question 1

What is the purpose of the 13.8KV Normal Auxiliary Power System?

Answer 1

The 13.8KV Normal Auxiliary Power System provides power to each Unit’s:

1. Auxiliary Electric Boiler(AEB)
2. Cooling Tower(CT) Fan Transformers

Question 2

What is the configuration of the 13.8KV Normal Auxiliary Power System?

Answer 2

Power is provided by the Main Generator, or the 230KV Switchyard as a backup, through the Isolated Phase Bus to a 22K/13.8K Auxiliary Transformer, 1ATE(2ATE). Power is supplied from the transformer to bus 1HTA(2HTA).

Question 3

What is the 13.8KV Normal Auxiliary Power System designator?

Answer 3

EPM

Question 4

What type of protective relaying do the 22KV/13.8KV ATE Transformers have?

Answer 4

1. The ATE transformers have the same protective relaying as the 22KV/6.9KV Unit Auxiliary Transformers.
2. The Protective Relaying provides a Zone A Lockout on:
   A. Neutral Ground
   B. Fault Pressure
   C. Liquid Level
   D. Transformer Differential

Question 5

What is type of design is the 22KV/13.8KV Auxiliary Transformers?

Answer 5

1. The design is similar to the Main and Unit Auxiliary Transformers.
2. There are 2 Cooling Banks of fans on each side of the transformers.
3. Isolation valves are provided for isolation to perform maintenance.
4. Fans and pumps cycle automatically as needed, or they can be started manually from the transformer control cabinet.

Question 6

What are the ATE Transformers rated for?

Answer 6

1. The ATE transformers are rated for 40MWe which can be a combination of the Auxiliary Boiler and the Cooling Tower Fans.
2. Procedurally we automatically limit the load to 36MWe at the Auxiliary Boiler A(B) Control Panel where this electrical load can be read.

Question 7

Which Buses are supplied by their respective ATE Transformers, and what are the loads on each?

Answer 7

1. 1ATE supplies bus 1HTA
2. 1HTA loads are:
   A. Auxiliary Electric Boiler A
   B. Transformers for Cooling Tower Fans 1A, 2A, 1C, and 2C
3. 2ATE supplies bus 2HTA
4. 2HTA loads are:
   A. Auxiliary Electric Boiler B
   B. Transformers for Cooling Tower Fans 1B, 2B, 1C, and 2C

Question 8

What are the Cooling Tower Fan Transformer designators?

Answer 8

1HTA:

1. 1TXJ
2. 2TXJ

2HTA:

1. 1TXK
2. 2TXK

Can be supplied by either bus:

1. 1TXL
2. 2TXL

Question 9

How many 600V MCCs are fed from the 6 Cooling Tower Fan Transformers?

Answer 9

There are eighteen total 600V MCCs, three to a transformer.

Question 10

What is checked at the transformers during operator rounds?

Answer 10

1. Liquid Temperature

2. Winding Temperature

Question 11

Why is nitrogen used in the Cooling Tower Fan Transformers, and what is checked on rounds?

Answer 11

1. There is a slight nitrogen overpressure on the transformers to prevent air or moisture intrusion which could lead to corrosion or decrease the electrical insulating value of the oil.
2. The transformer pressure gauge is checked to ensure pressure is greater than 0psig.

Question 12

What is the interlock associated with the 1C and 2C Cooling Tower Fans?

Answer 12

1. The 1C and 2C Cooling Tower Fans have an automatic swap feature since they can be powered from either 1HTA or 2HTA.
2. The purpose of the auto transfer is to ensure at least two groups of Cooling Tower fans per Unit will always have power.

Question 13

What controls the interlock associated with the 1C and 2C Cooling Tower Fans, and where is it operated from?

Answer 13

1. The 1HTA/2HTA Mode Select Switch(referred to as the AUTO/MAN Switch)
2. 2MC-11 in the Control Room

Question 14

What is required for an automatic transfer of the 1C and 2C Cooling Tower Fans to occur?

Answer 14

1. AUTO/MAN Switch in AUTO
2. Tie Breaker is OPEN
3. Undervoltage on the bus currently supplying the C Cooling Towers caused by something other than a lockout on the bus(no 86 relay)
4. Sources in sync(6 second time delay if not)

Question 15

What is required for a Manual transfer of the 1C and 2C Cooling Tower Fans to occur?

Answer 15

1. AUTO/MAN Switch in MAN
2. Depress CLOSE on the alternate feeder
3. The normal feeder will open, and the alternate will close
4. If sources are in sync a fast swap will occur
5. If not in sync the swap will occur after a 6 second delay

Question 16

What is the system interrelation with the Main Power Distribution System(EPA)?

Answer 16

The Main Power Distribution System provides 22KV power to the 1(2)ATE Transformers so that power can be provided to the Auxiliary Electric Boilers and the Cooling Tower Fans.

Question 17

What is the system interrelation with the Condenser Circulating Water System(RC)?

Answer 17

The Cooling Tower Fans remove heat from the Circulating Water which helps to maintain cycle efficiency and condenser vacuum. Without adequate heat removal Unit output may have to be reduced.

Question 18

What type of logic is there between the two normal feeder breakers and the tie breaker between 1HTA and 2HTA?

Answer 18

Only 2 out of 3 breakers can be closed at a time. If both normal feeder breakers are closed than there is a constant trip signal sent to the tie breaker.

Question 19

What is the affect of placing the 1HTA/2HTA Mode Select Switch(AUTO/MAN Switch) in MAN?

Answer 19

The automatic transfer of the 1C and 2C Cooling Tower Fans is defeated.

Question 20

When is it possible to close the HTA Tie Breaker?

Answer 20

The HTA Tie Breaker can be closed whether in AUTO or MAN provided no lockout relays are actuated and at least one of the 13.8KV normal feeder breakers are open.