Stator & Isophase Bus Cooling (CE)

Question 1

What is the purpose of these systems?

Answer 1

Stator Cooling: To provide cooling for the 
  main generator stator windings, 
  generator bushings, the rectifier 
  excitation system and the generator 
  lower frame extension

Isophase Bus Cooling: provides cooling 
  for the electrical buses from the main 
  generator terminals to the main power 
  transformer and the Unit Aux 
  Transformer

Question 2

What is the cooling medium for the stator cooling water heat exchangers?

Answer 2

TC

Question 3

What system supplies makeup water to stator cooling system?

Answer 3

DW

Question 4

What system provides cooling to the collector housing heat exchanger?

Answer 4

WC

Question 5

What is the capacity of the Stator Cooling Water pumps? Power source?

Answer 5

100% capacity pumps each

NG

Question 6

What would cause the standby Stator Cooling Water Pump to auto start?

Answer 6

In-service pump’s discharge pressure decreases below its low discharge set point

Question 7

What is the capacity of each Stator cooling cooler?

Answer 7

80% capacity

Question 8

What flows through the tubes of the cooler?

Answer 8

TC

Question 9

Where is the Stator Cooling Storage Tank located?

Answer 9

140’ Turbine Building

Question 10

What is the capacity of the tank?

Answer 10

1070 gallons

Question 11

What is the purpose of the deionizer?

Answer 11

Maintain low electrical conductivity by continuous removal of dissolve mineral salts

Question 12

How much of the Stator Cooling Water flow stream is directed through the deionizer?

Answer 12

~ 10%

Question 13

Where are the two test pushbuttons for the auto start of the standby pump?

Answer 13

Locally and in the Control Room

Question 14

While the plant is operating, the in-service discharge pressure drops low enough to start the standby pump. Pressure is returned to normal. What is the status of the standby pump?

Answer 14

Still running, it will need to be secured manually

Unless there’s a turbine trip of course

Question 15

What pressure is the stator cooling water being supplied to the main generator maintained at?

Answer 15

60 psig (the valve is locked in this throttle position)

Question 16

What temperature is stator cooling water maintained at prior to entering the generator inlet?

Answer 16

42 C

Question 17

How does the temperature control valve, TV-33, fail upon a loss of air?

Answer 17

Fails to the full cooling position

Question 18

What is the cooling medium for the Isophase Bus Cooling Coils?

Answer 18

TC

Question 19

What is the capacity of the Isophase Cooling Air Blowers?

Answer 19

100% capacity, both still operate at the same time however

Question 20

What powers these blowers?

Answer 20

NG

Question 21

What cools the collector housing?

Answer 21

A fan, attached to the main shaft of the generator, circulates air over the heat exchanger and through the exciter unit by the fan due to turbine rotation

Question 22

Where is the Stator Leak Monitoring System located?

Answer 22

At the Stator Cooling Water Skid

Question 23

What is the purpose of the SLMS?

Answer 23

To identify a stator bar leak as early as possible while the generator is in operation to allow enough time to plan for repair during the next outage

This is accomplished by monitoring the head tank vent for evidence of hydrogen

Question 24

What alarm signals are included on the new SLMS panel?

Answer 24

Hydrogen concentration >1.5%

Low air flow

Oxygen < 2ppm

Question 25

What happens upon a loss of Stator Cooling?

Answer 25

Will cause a turbine and generator trip that will cause entry into the load rejection procedure. The primary sensor for each trip initiates a 70 second time delay relay. When this relay is energized, the local and control room alarms are actuated. Unless the primary sensor returns to normal within the 70 second time frame, the turbine will trip

Question 26

How long may rated current be maintained for upon a loss of Isophase Bus Cooling?

Answer 26

30 min