GH- Generator Hydrogen

Question 1

Why was Hydrogen gas chosen as a cooling medium for the Generator?

Answer 1

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

Question 2

What do we use the Carbon Dioxide for?

Answer 2

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

Question 3

How do we determine how much Hydrogen or Carbon Dioxide is in the Generator?

Answer 3

Gas analyzer

determines in percentages the mixtures of the three possible gases in the generator depending on the operation in progress

Question 4

What is the general flow path of the Hydrogen in the Generator?

Answer 4

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

Question 5

What are the general steps in establishing a hydrogen atmosphere in the Generator?

Answer 5

Purge air from the Generator using CO2

Purge CO2 from the Generator with hydrogen to achieve a high percentage of hydrogen atmosphere

Question 6

What are the general steps in establishing an air atmosphere in the Generator?

Answer 6

Purge Hydrogen from the generator using CO2

Purge the CO2 from the generator with air to achieve a safe atmosphere for maintenance activities

Question 7

Where is the CO2 distribution tube located in the Generator? What other gas uses this same tube?

Answer 7

Bottom of the Generator

service air

Question 8

Where is the Hydrogen distribution tube located in the Generator? What else can it be used for?

Answer 8

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

Question 9

Where are main generator Purge operations controlled from?

Answer 9

Hydrogen Purge Station in the Turbine Building 140’ east end

Question 10

What system provides the CO2 to the main generator?

Answer 10

Fire protection vaporizer (cardox unit)

Question 11

What system provides the Hydrogen to the main generator?

Answer 11

Service Gases

Question 12

What system supplies dry air for purging carbon dioxide from the main generator?

Answer 12

Service Air

Question 13

In the Generator Hydrogen gas Coolers, what flows through the tubes?

Answer 13

Turbine Cooling Water

flow controlled by a temperature control valve and temp controller

Question 14

Where are the Generator Hydrogen Coolers located?

Answer 14

In the top of the Generator casing

Question 15

How do we prevent cross connecting hydrogen and CO2 at the manifold? During normal operations, where is this piece lined up to?

Answer 15

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

Question 16

What is the generator hydrogen pressure regulated at?

Answer 16

75 psig during normal operations

Question 17

What is the purpose of the Dryer Moisture Remover and where is it located?

Answer 17

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

Question 18

How does the Dryer Moisture Remover perform its function? What must be done to the dryer if the alumina changes to a pink color?

Answer 18

Contains activated alumina drying agent and removes moisture from the hydrogen flowing through it

Moisture must be removed by reactivation of the dryer

Question 19

What drives the Hydrogen through the Dryer Moisture Remover?

Answer 19

D/P developed by the shaft mounted fans in the generator

Question 20

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?

Answer 20

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

Question 21

What is the purpose of the GH Hydrogen Control Cabinet? Location?

Answer 21

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)

Question 22

What is the purpose of the GH Hydrogen Gas Analyzer? Location?

Answer 22

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

Question 23

What does a hydrogen purity of 75% correspond to in the GH system?

Answer 23

The upper explosive limit of the mixture

hydrogen must be purged before reaching this point

Question 24

What is the purpose of the GH Core Monitor?

Answer 24

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

Question 25

Where is the GH Core Monitor located? Where is the remote readout located? Major components of this system?

Answer 25

176’ Turbine Building

Remote Readout: control room, behind the horse shoe

gas control system, ion chamber, amplifier/power supply, meter and recorder

Question 26

What is the purpose of the Pyrolysate Collector in the GH system?

Answer 26

A device containing filter assemblies for obtaining pyrolysates from the generator hydrogen

Will start to sample when the core monitor goes into alarm

Question 27

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?

Answer 27

15 minutes

176’ Turbine Building

Question 28

What hydrogen purity band do we normally maintain in the main Generator?

Answer 28

90-100% (normally 99% or greater)

Question 29

What happens if we can’t keep Generator hydrogen purity above 80%?

Answer 29

The Generator must be shutdown and the hydrogen removed from the casing with carbon dioxide prior to reaching the explosive limit of 75%

Question 30

What is the maximum inlet hydrogen gas temperature to the main generator?

Answer 30

48C, ensures adequate cooling of the generator

Question 31

What is the minimum hydrogen gas pressure for which main generator operation is procedurally allowable?

Answer 31

30 psig, ensuring adequate gas density for proper cooling

Question 32

How can I get rid of the Hydrogen in the Generator if CO2 is lost?

Answer 32

Vented from the Generator

Question 33

What must be done if TC is lost to the GH coolers?

Answer 33

Main Generator must be tripped

Question 34

In the GH system what is the purpose of the 3-way valve?

Answer 34

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.

Question 35

Concerning the GH system, when the core monitor alarms, what happens for five to ten seconds prior to the pyrolysate collector sampling?

Answer 35

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