Generator Hydrogen and CO2 Flashcards
Why was hydrogen gas chosen as a cooling medium for generator?
it has a high thermal conductivity and because of its small size it provides low friction between the gas and moving parts of the generator
what do we use the carbon dioxide for?
purging oxygen and hydrogen
how do we determine how much hydrogen or carbon dioxide is in the generator?
Gas analyzer
Flow path of hydrogen in the generator?
1) flows between rotor and stator and thru the rotor body
2) internal components of the main gen excitation system
3)hydrogen cooled by cooler with TC and then circulated thru the gas dryer
4) a portion of flow passes thru core monitor and pyrolysate collector to monitor the generator for overheating
what are the general steps in establishing a hydrogen/air atmosphere in the generator?
purge air with CO2 and purge CO2 with Hydrogen
purge hydrogen with C02 and then air
Where is the CO2 distribution tube located in the generator?
bottom of the generator
Where is the hydrogen distribution tube located in the generator and what else can it be used for?
Top of the generator
can be the exit point for hydrogen, C02 or air depending on the purge operation
Where are purge operations controlled from
hydrogen purge station in the turbine 140’
What system supplies the purging air?
Service air
What cooling water is used for hydrogen cooler?
TC
Where is the hydrogen cooler located?
top of the generator
how do we prevent cross connecting the hydrogen and C02?
spool piece
What is the generator hydrogen pressure regulated at?
75 psig
What is the purpose of the dryer moisture remover and where is it located?
to help prevent damage to the generator system from corrosion due to moisture
located above the 140’ east turbine building
how does the dryer moisture remover perform its function?
activated alumina
What drives the hydrogen thru the dryer moisture remover?
DP developed by the shaft mounted fans in the generator
what must be done to the dryer if the alumina changes to a pink color?
moisture must be removed by reactivation of the dryer
How is reactivation performed?
isolating the dryer from the generator, aligning it to the suction of the seal oil systems vacuum pump and aligning an air inlet, then energizing a heater, contained in the dryer moisture remover unit
Why is it important that air flow is established prior to energizing the heater?
to prevent damage to the alumina crystal
How do you know the alumina is reactivated?
it is blue
what is the purpose of the hydrogen control cabinet?
provides ability to monitor the GH associated generator parameters and provide alarms to warn the operator of possible problems
What is the purpose of the hydrogen gas analyzer?
to monitor and provide indication of the generators hydrogen purity
purity must be maintained above 90% for effective cooling in the generator and if purity is allowed to lower to 80% the generator must be shut down
What does a hydrogen purity of 75% correspond to?
Upper explosive limit
What is the purpose of the core monitor?
provides immediate warning of local overheating in a gas cooled generator before extensive damage can result to the machine
The monitor detects thermal decomp of a small amount of material to see what component is wearing
Where is the remote readout for the core monitor located?
control room behind the horse shoe
What is the purpose of the pyrolysate collector?
a device containing filter assemblies for obtaining pyrolsates from the generator hydrogen
will start to sample when the core monitor goes into alarm
what is the nominal sample time for the generator at 75psig
15 mins
What hydrogen purity band do we normally maintain in the generator?
90-100% (normally 99%)
What is the sample flow rate of the core monitor?
500 standard cubic centimeters per minute
What happens if we cant keep hydrogen purity above 80%?
must shutdown and the hydrogen removed from the casing with C02 prior to reaching explosive limit of 75%
What is the max inlet hydrogen gas temp?
48C
What is minimum hydrogen pressure for which main generator operation is procedurally allowable?
30psig
how can I rid the hydrogen if C02 is not available?
vent to atmosphere
What must be done if TC is lost?
trip main gen
