Stator Core Cooling Water

Question 1

What are the four combinations of conditions that SCCW can give you a Unit Trip ?

Answer 1

low/very low flow + 5 sec time delay - amps > 15% power + run back for 135 second - amps > 15% power + no run back for 45 sec - very low flow 1 hour - hi cond > 1.5 micro-seimans for 175 sec

Question 2

What pressure must be kept above SCCW pressure always?

What must be done before filling SCCW after an outage?

What could pump manipulations at power cause inadvertantly?

Answer 2

• SCCW Press < H2 Press at all times
• Generator must be pressurized with H2 before filling SCCW
• pump manipulations at power may result in turbine runback

Question 3

why is there a 5 second time delay on SCCW run Back? Conditions for runback?

Answer 3

Allows time for stby pump to start Low/very low flow, 5 sec TD, > 15% phase B amps => 532 MW/min-> 125 MW (122 sec)

Question 4

Describe SCCW alignment and normal flowpath

Answer 4

One pump running/other in stby Suction from H2 pressurized head tank Discharge to two hx in series (100%)(one hx 75%) Through either; - filter, stator coils, head tank - demin, head tank

Question 5

Demineralizer configuration for each unit of SCCW ?

Answer 5

U-1 One H-OH demin normally in service for water purity. One Na-OH demin that automatically gets put into process stream when conductivity gets to low, this increases theoretical pH to minimize copper corrosion U-2 Two H-OH demins one in service/other in stby to maintain low conductivity so stator bars don’t pass current through water. (Never was air leak that led to copper corrosion)

Question 6

How are copper stator bars connected to SCCW system without conducting current from Generator?

Answer 6

-Conductivity of water is kept very low so water isn’t conductive -SCCW connects to stator bars through teflon tubes (insulator)

Question 7

Auto starts for SCCW pumps

Answer 7

• low pump d/p on other pump (20 psig)
• other pump contactor de-energized