Generator Hydrogen & CO2

Question 0

How is the hydrogen circulated in the generator?

Answer 0

There are two axial fans mounted one on each end of the generator rotor.

Question 1

State the purpose of the generator h2 system and CO2 system.

Answer 1

H2 cools the rotor and stator and the components of generator excitation.
CO2 provides a safe means of purging the main generator of H2 for either the establishment of a hydrogen atmosphere or purging the generator of hydrogen.

Question 2

Why is H2 used?

Answer 2

High thermal conductivity and small molecular size. This provides a low friction environment.

Question 3

Where is the CO2 distribution tube located in the generator?

Answer 3

Bottom of the generator

Question 4

Where is the H2 distribution tube located in the generator?

Answer 4

In the top of the generator.

Question 5

Where are purge operations controlled from?

Answer 5

The hydrogen purge station in the turbine building on the 140’.

Question 6

How many spool piece locations are there and why are they there?

Answer 6

2 locations, one spool piece. Blank flanges are put in the spot without the spool pieces. They are used to provide integrity and establish boundaries for flow paths.

Question 7

Where does the CO2 come from?

Answer 7

From the cardox unit in the fire protection system.

Question 9

Where does the H2 or air that’s being purged exit the generator?

Answer 9

Exits through the hydrogen distribution tube in the top of the generator and out to the purge station.

Question 10

Where does the CO2 that is purged with H2 exit the generator?

Answer 10

exits via the CO2 distribution header and is aligned to vent to atmosphere.

Question 11

What is needed to purge the generator of CO2 using H2?

Answer 11

there must be sufficient H2 available in the hydrogen banks of the service gas system.

Question 12

Where does the air come from that is used to purge the generator of CO2?

Answer 12

IA

Question 13

How is H2 temperature maintained in the generator?

Answer 13

a temperature instrument senses H2 temperature and sends a signal to a temperature control valve that regulates TC flow through the coolers to control temperature.

Question 14

Where is H2 added during normal operations to make up for losses?

Answer 14

to the H2 distribution tube located in the upper part of the generator casing

Question 15

What is generator H2 pressure regulated to during normal operation?

Answer 15

75 psig

Question 16

Why is the dryer moisture remover provided?

Answer 16

to prevent damage to the generator from corrosion due to moisture

Question 17

How is the dryer reactivated?

Answer 17

by isolating it from the generator and aligning it to the seal oil system’s vacuum pump, then energizing a heater in the dryer.

Question 18

What is located in the cabinet assembly with the stator cooling water controls and indications?

Answer 18

the hydrogen control cabinet and the seal oil controls and indications

Question 19

What can be monitored from the hydrogen control cabinet?

Answer 19

Generator gas pressure
Gas Hydrogen Purity
Generator Fan D/P
Generator gas Temp.

Question 20

What alarms are associated with the GH system?

Answer 20

Gas pressure High-Low
Gas Purity Low
Gas Temp High
Casing Liquid Detector Full

Question 21

What must H2 purity be maintained at?

Answer 21

above 90%, usually stays about 99%

Question 22

At what H2 purity must the generator be shut down?

Answer 22

80%. 75% is when it becomes explosive in contact with air and H2 must be purged from the generator before it gets to this purity

Question 23

What does the core monitor do?

Answer 23

provide immediate warning of local over heating in a gas cooled generator before extensive damage can result to the machine by detecting thermal decomposition of organic material used in the generator

Question 24

What does the pyrolysate collector do and what starts it?

Answer 24

it starts when the core monitor goes into alarm mode. It will collect H2 samples from the Generator for analysis via a generator 15 minute sample time.

Question 25

What is the sample flow rate through the core monitor?

Answer 25

5000 standard cubic centimeters per minute

Question 26

What is the maximum H2 inlet gas temperature?

Answer 26

48C to ensure adequate cooling of the generator

Question 27

What must be done if H2 purity can’t be maintained above 80%?

Answer 27

the generator must be shut down. A purge must be complete before purity reaches 75%

Question 28

What is the minimum H2 gas pressure in the generator?

Answer 28

30 psig must be maintained in order to operate.

Question 29

What must be done if TC is lost to the generator?

Answer 29

it must be tripped. If cooling is simply degraded, operation may continue, but at a reduced loading.

Question 30

Can we vent H2 from the generator without CO2 purging?

Answer 30

yes, but only in an emergency. it is vented from the generator only if there is a loss of CO2 along with an emergency need to remove the H2 from the generator.

Question 31

What happens on a loss of seal oil?

Answer 31

the generator is shutdown, shaft stopped, and hydrogen purged with CO2 if it is available.