Main Generator (MA) and Excitation

Question 1

When does the Gas Generator Monitoring System (GGMS) monitor and take samples?

Answer 1

Continuous monitor
Sample is taken when a generator overheating event is validated, the Pyrolysate Collector (located in Turbine Bldg, at 176’ elevation, adjacent to the Core Monitor) will collect a sample of the particulate.

Question 2

When do the main generator transformer fans start?

Answer 2

• The first group will start when the transformer is energized.
• The second and third groups will start when the transformer winding temperature reaches 70°C and 75°C respectively.

Question 3

How long do you have to downpower if isophase bus cooling is lost?

Answer 3

If the Isolated Phase Bus cooling is lost, rated (forced cooling) current may be maintained for 30 minutes. The Main Transformer bus section has a self-cooled rating of 23,000 amperes.

Question 4

What is stratification (in regards to the main transformers)?

Answer 4

Excessive circulation of cold oil can lead to a condition known as electric stratification. This condition can lead to large potentials within the transform tank. This potential difference eventually discharges, leading to damage. To prevent this condition the cooling pumps are **automatically tripped whenever a transformer is tripped **or current is removed from the transformer.

Question 5

What conditions are required for a coastdown trip?

Answer 5

• Turbine Trip
• Reverse Power condition
• Loss of power on NANS03 and/or NANS04
• Reactor Trip

The Main Generator stays connected to NANS01 and NANS02 until one of the following conditions is satisfied:
* 20 second timer times out
* NANS01 or NANS02 voltage reaches 80%