Stator Cooling(CE) Flashcards
What’re two separate subsystems for stator cooling ?
-Stator cooling water
-Isophase Bus Duct Cooling
What does Stator Cooling Water cool ?
-Cools Main Generator windings
-Cools Main Generator 24kv high voltage bushings
What does the Isophase Bus Duct Cooling do ?
Cools enclosed 24kv buses from Main Generator High Voltage bushing to the Main Transformers & Unit Aux. Transformer
What flow rates do the Stator Cooling Pump provide for each component ?
Stator windings: 660gpm
High Voltage Bushing:75gpm
Connection Ring Flow: 97gpm
What capacity is each Stator Cooling Pump? What is each pump powered by ?
-Each pump 100% capacity
-480VAC Load Center (NG)
When will standby Stator Cooling Pump automatically start?
-Starts if I’m service discharge pressure decreases below setpoint
What’re the low discharge setpoints for stator cooling water pumps ?
Pump discharge LO: 581gpm
Pump Discharge LO-LO: 549gpm
Where are the 2 test pushbuttons located for the Stator Cooling Pumps ?
Located in control room & on local Control Panel
How do the test pushbuttons work for the stator cooling pumps?
-Solenoid energizes that repositions three-way test valve that redirects discharge pressure away from running pump away from LP Switches
When standby pump auto starts when do they turn off ?
They will remain running until stopped manually
Where are the Stator Cooling Pumps powered from ?
Powered from 480VAC Load Center(NG)
What capacity are the Stator Cooling Coolers capacity ? How are the Coolers aligned
-80% capacity
-shell side is series (stator cooling)
-Tube side is aligned in parallel(Turbine Cooling
Which cooling water can be isolated from the Stator Cooling Water Coolers ?
Turbine cooling water has isolation capabilities
How do the Generator Inlet Duplex Strainers work ? When do they strainers need to be swapped ?
-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
Who swaps the duplex strainers? Who cleans the duplex strainers ?
-Operations perform swap
-Maintenance performs cleaning
What does stator cooling water tank do ?
-Accommodates changes in volume due to temperature changes
-Provides NPSH for pumps
-Provides means of detecting leakage into or out of system
What is Stator Cooling Water Tank makeup water ?
DW supplies makeup water to tank
What is Instrument Air used for inside the Stator Cooling Water Tank ?
-Stator Leak Monitoring system supplies instrument air as cover gas to maintain oxygen concentration of water above minimum level
Why is instrument air cover gas necessary ?
-Forms protective oxide layer on copper stator bars to minimize erosion & Leakage
-Can also be used to purge hydrogen out the tanks vent
What is the Stator Cooling Water Tank vent used for ? What is the vent monitored by ?
-Used to vent off hydrogen via instrument air
-Monitored by Stator Leak Monitoring System to detect hydrogen
-Vent is directed to Turbine Building Roof
Why must you be careful when filling Stator cooling water tank ?
Be careful not to overfill & flood sampling line
What does the Stator Leak Monitoring system do ?
Identifies Stator Cooling leak inside the generator casing while it’s operating
How does Stator Leak Monitoring system work ?
-Monitors stator cooling Water tank vent
-Identifies hydrogen leakage trends, which can identify stator bar leak before insulation is damaged
What oxygen concentration can corrosion occur at in stator bars ?
When Stator Cooling Water drops below 0.5ppm oxygen
What is the normal oxygen concentration of water in stator cooling water tank ? How does Hydrogen leakage blankets stator cooling water ?
-Normally between 2 & 8ppm
-since leakage of hydrogen blankets stator cooling water surface from atmosphere it’ll decrease oxygen concentration
What’re the Stator Cooling Filters & Deionizer do ?
Filters & deionizes are to purify water
What’re the 3 filters in the system used for ?
-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
What is the Mixed Bed Deminerlizer ?
-Continuously removes dissolved mineral salts in system to low electrical conductivity
-Throttle valve maintains 100gpm through deionizer
What does the pressure control valve (PV-34) do ?
-Controls stator cooling water pressure supplied to main generator @60psig
-Valve locked in throttled position
What does FCV-12 do ?
-Adjusts coolant flow to Generator High Voltage Bushings
-Valve set based on percentage of total available flow required by each section
What does the Temperature Control Valve (TCV-33) do ?
Temperature controller causes TV-33 to control bypass flow around Stator Cooling HEX to maintain 42C at Generator Inlet
What position will the TV-33 fail to?
Fails to full cooling through Stator Cooling HEX on loss of air signal
Where are the Stator Cooling Pump started from ?
-One pump started from Control Room
-Second pump placed in standby
If any of the pressure switches activates due to Low Flow to the Stator, Connection Ring, & high voltage bushings what happens ?
-Initiates 70second delay to trip Main Turbine
-If flow returns above setpoint before 70 seconds, than timer will reset
Where do the two Isophase Bus Duct Cooler Blowers discharge to ? Where does common header discharge to ?
-Discharge into separate ducts & then combine into a common header
-Common header discharges to ‘B’ phase bud duct
What does the Isophase Bus Ducts cool ?
It cools:
- ‘A’ ‘B’ ‘C’ high voltage bushings
-Main Transformer
-Aux. Transformer
-Generator Potential Transformers
How many Isophase Bus Duct Blowers are in service normally ?
They’re both 100% capacity
-Both fans operate together since one blower cause low flow alarms
Where are Isophase Bus Duct Blowers operated from ?
Operated locally by opening or closing their load center
How is the air that passes through Isophase Bus Ducts cooled ?
It cooled by HEX at suction of blower that has Turbine Cooling water passing through it
What’s main purpose for Isophase Bus Ducts ?
Cools Isophase conductors
Where do the Isophase bus duct blowers draw air from ?
Draws air from turbine building & mixes with returning air, then gets cooled by HEX & discharges back into Isophase Bus Ducts
How do the discharge dampers operate for the Isophase Bus Duct Blowers ?
-Dampers open up when blower starts
-When blower is not operating, damper will close to prevent back flow from other blower
Why is humidity sensor installed into the isophase blower housing ?
-Excessive makeup to system due to excessive leakage
-Cooler leakage
Where is makeup air supplied to the Isophase bus ducts from ?
Supplied makeup air from turbine building through makeup air filter
What does Isophase Bus Duct Hydrogen Detection system ?
Monitors Isophase bus ducts for hydrogen leakage from Main Generator through high voltage bushings
What does the Isophase Bus Duct Hydrogen detection use ?
Uses Quadraflex Digital Multi-Channel Gas Detection consists instrument control module & detectors/transmitter
How does the Isophase Bus Duct Hydrogen Detection work?
Takes sample for hydrogen in Isophase bus ducts near each High Voltage Bushings & at Generator neutral bus enclosure
Whatre the two sections the instrument Control Module divided into ?
Divided into:
-Digital Display & Command Section
-Analogue Alarm Display
What is the Max/Auto switch users for on the Digital Display & Command Section?
-“Max” maintains chan & %LFL displays on highest value channel
-“Auto” cycles through each of channels every three seconds
What does %LFL do on the Digital Display & command Section ?
Displays %LFL for hydrogen concentration in air for selected channel
What does the Digital Display & Command Section, Norm/Hold/Advance switch used for ?
-“Norm” permits “Auto” operation of Max/Auto switch
-“Hold” maintains displays of single display
-“Adv” manually selects next channel for display
What’re the 3 status LEDs provided for each channel on Analogue Alarm Display Section?
-Warn
-Alarm
-Fail
When would the Fail LED flash ? How is it reset ?
-Power failure
-Sensor/Transmitter failure
-Initial Startup
Reset pushbuttons will reset any analogue alarm display section flashing lights
What happens if Isophase Bus Hydrogen Gas reaches 25% Lower Flammability Limit ?
-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
What happens on loss of one Isophase Bus Duct Blower? What happens if you lose both blowers ?
-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
What does the Main Generator Collector Housing Cooling Unit do ?
Provides cooling to Main Generator Collector Housing
How does the Main Generator Collector Housing Cooling unit operate ?
There is a normal chilled HEX & shaft mounted fan circulates through HEX
