Stator Cooling/Isophase bus cooling

Question 1

What does the stator cooling system do?

Answer 1

Provides cooling for the stator windings, terminal bushings, excitation rectifiers and connection rings.

Question 2

Where does stator cooling enter and leave the main generator?

Answer 2

At the top of the generator to prevent uncovering the stator bars on a loss of system flow.

Question 3

What pressure is stator cooling coolant leaving the generator maintained at? Why?

Answer 3

ATM pressure to help remove H2 picked up by the coolant.

Question 4

Where is the H2 removed from the coolant and where does it go?

Answer 4

It is removed at the storage tank and is vented to the roof

Question 5

Explain the cooling mechanism for the CE system.

Answer 5

2 series HX cooled by TCW

Question 6

What is the CE supply temperature maintained at?

Answer 6

Approx. 42 degrees C

Question 7

Can CE flow be isolated to a cooler? Can TCW?

Answer 7

CE flow can not be isolated. TCW can be. The main generators output will have to be reduced to approx. 80 percent.

Question 8

What valve maintains pressure of the coolant going to the Main Generator?

Answer 8

PCV-34 at around 22-28 psig

Question 9

Explain the Stator cooling pumps

Answer 9

2 pumps. 1 normally running and one in standby.
Powered from NGN-L14 and L15
Standby pump starts at CE lo flow 581 GPM.
Both pumps receive another start signal at a lo-lo flow of 549 gpm.

Question 10

If the standby CE pump autostarts; what indication does the control room see?

Answer 10

Amber light

Question 11

What are the CE pump trips?

Answer 11

• Gen differential
• Stator Ground
• Unit differential lock

Question 12

What provides cooling to the isophase and stator cooling coolers?

Answer 12

TCW

Question 13

What provides makeup to the CE system?

Answer 13

DW

Question 14

How is conductivity maintained in the CE system?

Answer 14

10 percent of system flow goes thru a deionizer (resin) to remove impurities.

Question 15

When do we need to change the resin in the deionizer?

Answer 15

delta-P greater than 15 psid

conductivity greater than 0.5 micro uhmo/cm

Question 16

What does the stator leak monitoring system (SLMS) do for us?

Answer 16

Detects H2 concentration in storage tank

Helps find leaks early which help prevent insulation damage and electrical malfunctions.

Question 17

What are the CE malfunctions that cause a MT trip?

Answer 17

All CE trips have a 70 second time delay

• Low inlet water pressure (549 gpm)
• High outlet temperature (85 degrees F)
• Stator in flow (549 gpm)
• Connection ring flow (90 gpm)
• Gen. Bushing flow (64 gpm)
• Rectifier flow (54 gpm)

Question 18

What is the isophase bus temperature limit?

Answer 18

105 degrees C

Question 19

What is the enclosure temperature limit?

Answer 19

80 degrees C

Question 20

How many fans are in the Isophase system?

Answer 20

2 100 percent capacity fans powered from L15 and L14

Question 21

What does the H2 gas detector in the isophase system do?

Answer 21

Alarms in control room on hi or hi hi. Indicative of a Bushing failure.

Question 22

What do the operators need to do on a Hi H2 alarm in the isophase bus system?

Answer 22

On a Hi alarm the H2 pressure needs to be reduced.

Question 23

What do the operators need to do on a hi-hi H2 alarm in the isophase bus system?

Answer 23

The generator needs to be removed from service and the bushings repaired.