GH- Generator Hydrogen Flashcards
Why was Hydrogen gas chosen as a cooling medium for the Generator?
It has a high thermal conductivity and, because of its small molecular size, provides a low friction environment between the gas and the moving parts of the generator
rotor is cooled by a flow of hydrogen gas between the rotor and stator and
through the ventilation passages in the rotor body and through the stator components
What do we use the Carbon Dioxide for?
Used as an intermediate gas when performing operations involving the initial establishment of a hydrogen atmosphere or the venting off of a hydrogen atmosphere from the generator
How do we determine how much Hydrogen or Carbon Dioxide is in the Generator?
Gas analyzer
determines in percentages the mixtures of the three possible gases in the generator depending on the operation in progress
What is the general flow path of the Hydrogen in the Generator?
Flows between the rotor and stator and through the ventilation passages in the rotor body
Internal components of the main generator excitation system are located in the flow path of the hydrogen and thus are cooled by the hydrogen
Hydrogen is then cooled by a cooler, which the heat sink is TC, and is then circulated through a gas dryer to remove moisture
A portion of the flow also passes through a core monitor and a pyrolysate collector to monitor the generator for over-heating
What are the general steps in establishing a hydrogen atmosphere in the Generator?
Purge air from the Generator using CO2
Purge CO2 from the Generator with hydrogen to achieve a high percentage of hydrogen atmosphere
What are the general steps in establishing an air atmosphere in the Generator?
Purge Hydrogen from the generator using CO2
Purge the CO2 from the generator with air to achieve a safe atmosphere for maintenance activities
Where is the CO2 distribution tube located in the Generator? What other gas uses this same tube?
Bottom of the Generator
service air
Where is the Hydrogen distribution tube located in the Generator? What else can it be used for?
Top of the generator
Can be the exit point for hydrogen, carbon dioxide, or air depending on the purge operation that is in progress at the time
Where are main generator Purge operations controlled from?
Hydrogen Purge Station in the Turbine Building 140’ east end
What system provides the CO2 to the main generator?
Fire protection vaporizer (cardox unit)
What system provides the Hydrogen to the main generator?
Service Gases
What system supplies dry air for purging carbon dioxide from the main generator?
Service Air
In the Generator Hydrogen gas Coolers, what flows through the tubes?
Turbine Cooling Water
flow controlled by a temperature control valve and temp controller
Where are the Generator Hydrogen Coolers located?
In the top of the Generator casing
How do we prevent cross connecting hydrogen and CO2 at the manifold? During normal operations, where is this piece lined up to?
One moveable spool piece that must be installed in either the hydrogen supply piping or the CO2 supply piping to the generator
To supply hydrogen to the generator
What is the generator hydrogen pressure regulated at?
75 psig during normal operations
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, same platform as SO hydrogen detraining section float valve
How does the Dryer Moisture Remover perform its function? What must be done to the dryer if the alumina changes to a pink color?
Contains activated alumina drying agent and removes moisture from the hydrogen flowing through it
Moisture must be removed by reactivation of the dryer
What drives the Hydrogen through the Dryer Moisture Remover?
D/P developed by the shaft mounted fans in the generator
Concerning the GH dryer moisture remover, how is Reactivation performed? Why is it important that the air flow path is established prior to energizing the heater? How would I know that the Reactivation is complete?
Isolating the dryer from the generator, aligning it to the suction of the Seal Oil system’s vacuum pump and aligning an air inlet, then energizing a heater, contained in the Dryer Moisture Remover unit
To prevent damage to the alumina crystals
When the blue color returns to the crystals
What is the purpose of the GH Hydrogen Control Cabinet? Location?
Provides the operator with the ability to monitor the GH associated generator parameters and provide alarms to warn the operator of possible problems
140’ turbine building
(shares cabinet with CE and SO)
What is the purpose of the GH Hydrogen Gas Analyzer? Location?
To monitor and provide indication of the generator’s 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
on the GH hydrogen control cabinet
What does a hydrogen purity of 75% correspond to in the GH system?
The upper explosive limit of the mixture
hydrogen must be purged before reaching this point
What is the purpose of the GH Core Monitor?
A sensitive instrument designed to provide immediate warning of local overheating in a gas cooled generator before extensive damage can result to the machine
The monitor detects thermal decomposition of a small amount of organic material used in the generator.
This decomposition produces a large number of small particles, which are detected by the core monitor much the same way that a smoke detector detects smoke
Where is the GH Core Monitor located? Where is the remote readout located? Major components of this system?
176’ Turbine Building
Remote Readout: control room, behind the horse shoe
gas control system, ion chamber, amplifier/power supply, meter and recorder
What is the purpose of the Pyrolysate Collector in the GH system?
A device containing filter assemblies for obtaining pyrolysates from the generator hydrogen
Will start to sample when the core monitor goes into alarm
Concerning the GH system pyrolysate collector, what is the nominal sample time for the generator at 75 psig? Where is the GH Pyrolysate Collector located?
15 minutes
176’ Turbine Building
What hydrogen purity band do we normally maintain in the main Generator?
90-100% (normally 99% or greater)
What happens if we can’t keep Generator hydrogen purity above 80%?
The Generator must be shutdown and the hydrogen removed from the casing with carbon dioxide prior to reaching the explosive limit of 75%
What is the maximum inlet hydrogen gas temperature to the main generator?
48C, ensures adequate cooling of the generator
What is the minimum hydrogen gas pressure for which main generator operation is procedurally allowable?
30 psig, ensuring adequate gas density for proper cooling
How can I get rid of the Hydrogen in the Generator if CO2 is lost?
Vented from the Generator
What must be done if TC is lost to the GH coolers?
Main Generator must be tripped
In the GH system what is the purpose of the 3-way valve?
to select whether the CO2 distribution tube in the generator is aligned to receive either air or CO2, or is aligned to the section of piping used to vent the system to atmosphere.
Concerning the GH system, when the core monitor alarms, what happens for five to ten seconds prior to the pyrolysate collector sampling?
gas from the generator is passed through the inlet lines and to the vent to atmosphere to purge the lines of dust, dirt and oxide that might contaminate the sample
