Stator Cooling(CE)

Question 1

What’re two separate subsystems for stator cooling ?

Answer 1

-Stator cooling water
-Isophase Bus Duct Cooling

Question 2

What does Stator Cooling Water cool ?

Answer 2

-Cools Main Generator windings
-Cools Main Generator 24kv high voltage bushings

Question 3

What does the Isophase Bus Duct Cooling do ?

Answer 3

Cools enclosed 24kv buses from Main Generator High Voltage bushing to the Main Transformers & Unit Aux. Transformer

Question 4

What flow rates do the Stator Cooling Pump provide for each component ?

Answer 4

Stator windings: 660gpm
High Voltage Bushing:75gpm
Connection Ring Flow: 97gpm

Question 5

What capacity is each Stator Cooling Pump? What is each pump powered by ?

Answer 5

-Each pump 100% capacity
-480VAC Load Center (NG)

Question 6

When will standby Stator Cooling Pump automatically start?

Answer 6

-Starts if I’m service discharge pressure decreases below setpoint

Question 7

What’re the low discharge setpoints for stator cooling water pumps ?

Answer 7

Pump discharge LO: 581gpm
Pump Discharge LO-LO: 549gpm

Question 8

Where are the 2 test pushbuttons located for the Stator Cooling Pumps ?

Answer 8

Located in control room & on local Control Panel

Question 9

How do the test pushbuttons work for the stator cooling pumps?

Answer 9

-Solenoid energizes that repositions three-way test valve that redirects discharge pressure away from running pump away from LP Switches

Question 10

When standby pump auto starts when do they turn off ?

Answer 10

They will remain running until stopped manually

Question 11

Where are the Stator Cooling Pumps powered from ?

Answer 11

Powered from 480VAC Load Center(NG)

Question 12

What capacity are the Stator Cooling Coolers capacity ? How are the Coolers aligned

Answer 12

-80% capacity
-shell side is series (stator cooling)
-Tube side is aligned in parallel(Turbine Cooling

Question 13

Which cooling water can be isolated from the Stator Cooling Water Coolers ?

Answer 13

Turbine cooling water has isolation capabilities

Question 14

How do the Generator Inlet Duplex Strainers work ? When do they strainers need to be swapped ?

Answer 14

-one strainer is in service & other strainer in standby, can be swapped without interrupting operation
-Strainers need to be swapped when high DP across strainer is sensed

Question 15

Who swaps the duplex strainers? Who cleans the duplex strainers ?

Answer 15

-Operations perform swap
-Maintenance performs cleaning

Question 16

What does stator cooling water tank do ?

Answer 16

-Accommodates changes in volume due to temperature changes
-Provides NPSH for pumps
-Provides means of detecting leakage into or out of system

Question 17

What is Stator Cooling Water Tank makeup water ?

Answer 17

DW supplies makeup water to tank

Question 18

What is Instrument Air used for inside the Stator Cooling Water Tank ?

Answer 18

-Stator Leak Monitoring system supplies instrument air as cover gas to maintain oxygen concentration of water above minimum level

Question 19

Why is instrument air cover gas necessary ?

Answer 19

-Forms protective oxide layer on copper stator bars to minimize erosion & Leakage
-Can also be used to purge hydrogen out the tanks vent

Question 20

What is the Stator Cooling Water Tank vent used for ? What is the vent monitored by ?

Answer 20

-Used to vent off hydrogen via instrument air
-Monitored by Stator Leak Monitoring System to detect hydrogen
-Vent is directed to Turbine Building Roof

Question 21

Why must you be careful when filling Stator cooling water tank ?

Answer 21

Be careful not to overfill & flood sampling line

Question 22

What does the Stator Leak Monitoring system do ?

Answer 22

Identifies Stator Cooling leak inside the generator casing while it’s operating

Question 23

How does Stator Leak Monitoring system work ?

Answer 23

-Monitors stator cooling Water tank vent
-Identifies hydrogen leakage trends, which can identify stator bar leak before insulation is damaged

Question 24

What oxygen concentration can corrosion occur at in stator bars ?

Answer 24

When Stator Cooling Water drops below 0.5ppm oxygen

Question 25

What is the normal oxygen concentration of water in stator cooling water tank ? How does Hydrogen leakage blankets stator cooling water ?

Answer 25

-Normally between 2 & 8ppm -since leakage of hydrogen blankets stator cooling water surface from atmosphere it’ll decrease oxygen concentration

Question 26

What’re the Stator Cooling Filters & Deionizer do ?

Answer 26

Filters & deionizes are to purify water

Question 27

What’re the 3 filters in the system used for ?

Answer 27

-Generator inlet filter, filters water to Generator Stator -Rectifier Inlet Filter, filters water going to Generator High Voltage Bushings -Makeup Water filter that filters DW used as makeup for Stator Cooling Tank

Question 28

What is the Mixed Bed Deminerlizer ?

Answer 28

-Continuously removes dissolved mineral salts in system to low electrical conductivity -Throttle valve maintains 100gpm through deionizer

Question 29

What does the pressure control valve (PV-34) do ?

Answer 29

-Controls stator cooling water pressure supplied to main generator @60psig -Valve locked in throttled position

Question 30

What does FCV-12 do ?

Answer 30

-Adjusts coolant flow to Generator High Voltage Bushings -Valve set based on percentage of total available flow required by each section

Question 31

What does the Temperature Control Valve (TCV-33) do ?

Answer 31

Temperature controller causes TV-33 to control bypass flow around Stator Cooling HEX to maintain 42C at Generator Inlet

Question 32

What position will the TV-33 fail to?

Answer 32

Fails to full cooling through Stator Cooling HEX on loss of air signal

Question 33

Where are the Stator Cooling Pump started from ?

Answer 33

-One pump started from Control Room -Second pump placed in standby

Question 34

If any of the pressure switches activates due to Low Flow to the Stator, Connection Ring, & high voltage bushings what happens ?

Answer 34

-Initiates 70second delay to trip Main Turbine -If flow returns above setpoint before 70 seconds, than timer will reset

Question 35

Where do the two Isophase Bus Duct Cooler Blowers discharge to ? Where does common header discharge to ?

Answer 35

-Discharge into separate ducts & then combine into a common header -Common header discharges to ‘B’ phase bud duct

Question 36

What does the Isophase Bus Ducts cool ?

Answer 36

It cools: - ‘A’ ‘B’ ‘C’ high voltage bushings -Main Transformer -Aux. Transformer -Generator Potential Transformers

Question 37

How many Isophase Bus Duct Blowers are in service normally ?

Answer 37

They’re both 100% capacity -Both fans operate together since one blower cause low flow alarms

Question 38

Where are Isophase Bus Duct Blowers operated from ?

Answer 38

Operated locally by opening or closing their load center

Question 39

How is the air that passes through Isophase Bus Ducts cooled ?

Answer 39

It cooled by HEX at suction of blower that has Turbine Cooling water passing through it

Question 40

What’s main purpose for Isophase Bus Ducts ?

Answer 40

Cools Isophase conductors

Question 41

Where do the Isophase bus duct blowers draw air from ?

Answer 41

Draws air from turbine building & mixes with returning air, then gets cooled by HEX & discharges back into Isophase Bus Ducts

Question 42

How do the discharge dampers operate for the Isophase Bus Duct Blowers ?

Answer 42

-Dampers open up when blower starts -When blower is not operating, damper will close to prevent back flow from other blower

Question 43

Why is humidity sensor installed into the isophase blower housing ?

Answer 43

-Excessive makeup to system due to excessive leakage -Cooler leakage

Question 44

Where is makeup air supplied to the Isophase bus ducts from ?

Answer 44

Supplied makeup air from turbine building through makeup air filter

Question 45

What does Isophase Bus Duct Hydrogen Detection system ?

Answer 45

Monitors Isophase bus ducts for hydrogen leakage from Main Generator through high voltage bushings

Question 46

What does the Isophase Bus Duct Hydrogen detection use ?

Answer 46

Uses Quadraflex Digital Multi-Channel Gas Detection consists instrument control module & detectors/transmitter

Question 47

How does the Isophase Bus Duct Hydrogen Detection work?

Answer 47

Takes sample for hydrogen in Isophase bus ducts near each High Voltage Bushings & at Generator neutral bus enclosure

Question 48

Whatre the two sections the instrument Control Module divided into ?

Answer 48

Divided into: -Digital Display & Command Section -Analogue Alarm Display

Question 49

What is the Max/Auto switch users for on the Digital Display & Command Section?

Answer 49

-“Max” maintains chan & %LFL displays on highest value channel -“Auto” cycles through each of channels every three seconds

Question 50

What does %LFL do on the Digital Display & command Section ?

Answer 50

Displays %LFL for hydrogen concentration in air for selected channel

Question 51

What does the Digital Display & Command Section, Norm/Hold/Advance switch used for ?

Answer 51

-“Norm” permits “Auto” operation of Max/Auto switch -“Hold” maintains displays of single display -“Adv” manually selects next channel for display

Question 52

What’re the 3 status LEDs provided for each channel on Analogue Alarm Display Section?

Answer 52

-Warn -Alarm -Fail

Question 53

When would the Fail LED flash ? How is it reset ?

Answer 53

-Power failure -Sensor/Transmitter failure -Initial Startup Reset pushbuttons will reset any analogue alarm display section flashing lights

Question 54

What happens if Isophase Bus Hydrogen Gas reaches 25% Lower Flammability Limit ?

Answer 54

-Generator hydrogen pressure will be lowered to slow leakage from Main Generator through High Voltage Bushings -Ultimately Main Generator will have to be taken offline to repair bushings

Question 55

What happens on loss of one Isophase Bus Duct Blower? What happens if you lose both blowers ?

Answer 55

-Loss of one blower won’t affect plant operation -Loss of second blower would leave Isophase bus duct to self cooling via natural convection -Generator loading would need to be reduced within 30 minutes on loss of both blowers

Question 56

What does the Main Generator Collector Housing Cooling Unit do ?

Answer 56

Provides cooling to Main Generator Collector Housing

Question 57

How does the Main Generator Collector Housing Cooling unit operate ?

Answer 57

There is a normal chilled HEX & shaft mounted fan circulates through HEX