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Systems > Stator Cooling(CE) > Flashcards

Stator Cooling(CE) Flashcards

1
Q

What’re two separate subsystems for stator cooling ?

A

-Stator cooling water
-Isophase Bus Duct Cooling

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2
Q

What does Stator Cooling Water cool ?

A

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

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3
Q

What does the Isophase Bus Duct Cooling do ?

A

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

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4
Q

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

A

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

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5
Q

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

A

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

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6
Q

When will standby Stator Cooling Pump automatically start?

A

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

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7
Q

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

A

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

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8
Q

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

A

Located in control room & on local Control Panel

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9
Q

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

A

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

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10
Q

When standby pump auto starts when do they turn off ?

A

They will remain running until stopped manually

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11
Q

Where are the Stator Cooling Pumps powered from ?

A

Powered from 480VAC Load Center(NG)

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12
Q

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

A

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

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13
Q

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

A

Turbine cooling water has isolation capabilities

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14
Q

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

A

-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

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15
Q

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

A

-Operations perform swap
-Maintenance performs cleaning

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16
Q

What does stator cooling water tank do ?

A

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

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17
Q

What is Stator Cooling Water Tank makeup water ?

A

DW supplies makeup water to tank

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18
Q

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

A

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

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19
Q

Why is instrument air cover gas necessary ?

A

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

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20
Q

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

A

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

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21
Q

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

A

Be careful not to overfill & flood sampling line

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22
Q

What does the Stator Leak Monitoring system do ?

A

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

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23
Q

How does Stator Leak Monitoring system work ?

A

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

24
Q

What oxygen concentration can corrosion occur at in stator bars ?

A

When Stator Cooling Water drops below 0.5ppm oxygen

25
Q

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

A

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

26
Q

What’re the Stator Cooling Filters & Deionizer do ?

A

Filters & deionizes are to purify water

27
Q

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

A

-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

28
Q

What is the Mixed Bed Deminerlizer ?

A

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

29
Q

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

A

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

30
Q

What does FCV-12 do ?

A

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

31
Q

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

A

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

32
Q

What position will the TV-33 fail to?

A

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

33
Q

Where are the Stator Cooling Pump started from ?

A

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

34
Q

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

A

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

35
Q

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

A

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

36
Q

What does the Isophase Bus Ducts cool ?

A

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

37
Q

How many Isophase Bus Duct Blowers are in service normally ?

A

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

38
Q

Where are Isophase Bus Duct Blowers operated from ?

A

Operated locally by opening or closing their load center

39
Q

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

A

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

40
Q

What’s main purpose for Isophase Bus Ducts ?

A

Cools Isophase conductors

41
Q

Where do the Isophase bus duct blowers draw air from ?

A

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

42
Q

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

A

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

43
Q

Why is humidity sensor installed into the isophase blower housing ?

A

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

44
Q

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

A

Supplied makeup air from turbine building through makeup air filter

45
Q

What does Isophase Bus Duct Hydrogen Detection system ?

A

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

46
Q

What does the Isophase Bus Duct Hydrogen detection use ?

A

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

47
Q

How does the Isophase Bus Duct Hydrogen Detection work?

A

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

48
Q

Whatre the two sections the instrument Control Module divided into ?

A

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

49
Q

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

A

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

50
Q

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

A

Displays %LFL for hydrogen concentration in air for selected channel

51
Q

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

A

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

52
Q

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

A

-Warn
-Alarm
-Fail

53
Q

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

A

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

54
Q

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

A

-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

55
Q

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

A

-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

56
Q

What does the Main Generator Collector Housing Cooling Unit do ?

A

Provides cooling to Main Generator Collector Housing

57
Q

How does the Main Generator Collector Housing Cooling unit operate ?

A

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

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