Stator & Isophase Cooling Water

Question 1

What is the purpose of CE?

Answer 1

Stator cooling provides cooling for:
  main generator stator windings
  generator bushings
  rectifier excitation system
  generator lower frame extension
Isophase bus cooling:
  independent cooling for electrical buses from main generator terminals to the main power transformer and aux transformer

Question 2

What is the pump and heat exchanger configuration in the stator cooling system?

Answer 2

2- 100% capacity pumps in parallel

2 - coolers in series

Question 3

What cools the stator cooling heat exchangers?

Answer 3

TC

Question 4

How is TC run through the heat exchangers?

Answer 4

it is run in parallel so that TC can be isolated to one HX and the other still be in service.

Question 5

Describe the Isophase cooling system.

Answer 5

motor driven fan, air to water HX, and an air plenum to force air cool the isophase bus.
two units with a common air plenum, both operating at the same time.

Question 6

What supplies makeup water to the stator cooling system?

Answer 6

DW

Question 7

What cools the collector housing heat exchanger?

Answer 7

WC

Question 8

What will cause the standby stator cooling pump to trip?

Answer 8

the in service pump’s discharge pressure falling below its low discharge setpoint. There is 2/3 logic for this.

Question 9

What are the power supplies for the stator cooling water pumps?

Answer 9

NG

Question 10

What is the capacity of the stator water coolers?

Answer 10

Each is 80% capacity, so if TC is removed from one of the coolers, generator load must be reduced to at least 80%

Question 11

How does the stator cooling water temp control valve fail?

Answer 11

through the cooler

Question 12

What is the purpose of the stator cooling storage tank?

Answer 12

NPSH for the pumps & to compensate for variations in water volume due to temperature and the presence of gases in the water.

Question 13

What does the deionizer do?

Answer 13

maintain stator cooling water at a low conductivity by continuous removal of dissolved mineral salts in the mixed bed deionizer. It continuously deionizes 10% of the stator cooling flow stream.

Question 14

Where can the automatic function of the standby stator cooling water pump be tested from?

Answer 14

control room or at the local control panel.

Question 15

What happens to a pump that was auto started if the original pump returns to service?

Answer 15

it will continue to run until it is manually shutdown and returned to standby

Question 16

What pressure is stator cooling water supplied to the generator at and how is it controlled?

Answer 16

60 psig and it is controlled by using the pressure control valve PV-34 (normally locked throttled)

Question 17

How is flow controlled to the generator bushings and rectifier excitation system?

Answer 17

manually using FCV-12 & FCv-13

Question 18

What stator cooling water temperature does TV-33 maintain at the generator inlet?

Answer 18

42C

Question 19

How is cooling flow to the isophase bus controlled?

Answer 19

manually by throttling the cooler outlet valve

Question 20

Where are the isophase bus fans controlled from?

Answer 20

locally at the load center supply breakers (NG)

Question 21

How is the main generator collector housing cooled?

Answer 21

by a fan attached to the main shaft of the generator that circulates are over a heat exchanger that has WC flowing through it and then through the exciter unit.

Question 22

How does the stator leak monitoring system work?

Answer 22

it monitors the head tank vent for the presence of hydrogen.

Question 23

What else does the SLMS system do?

Answer 23

it provides a method of increasing stator cooling water O2 level by allowing for air injection into the system head tank.

Question 24

How long after a stator cooling water trouble alarm do you have to reset it or fix the problem before the turbine trips?

Answer 24

70 seconds.

Question 25

What must be done if isophase bus cooling is lost?

Answer 25

normal 34,000 amps may be maintained for up to 30 minutes, but after that, you must reduce to 23,000 amps for the unit to be as self sustaining cooling.