Class Load Centers & MCC’s (PG/PH)

Question 1

How many MCC’s on each train ?

Answer 1

Four 480VAC MCCS & two non class SIAS load shed MCC on each train

Question 2

How many class load centers(PG) on the class bus(PB) ?

Answer 2

3 480VAC Load centers on each train

Question 3

How are PGA/PGB L33,35,34,36 load centers cools ?

Answer 3

They’re cooled by natural circulation and rated at 750KVA

Question 4

How’re PGA/PGB L31&32 cooled ?

Answer 4

They’re cooled by natural air circulation,until 180 degrees Celsius set point and then it’s forced air & they’re rated at 1000KVA

Question 5

How’re the cooling fans controlled on L31 & L32?

Answer 5

Theyre controlled by a Electronic Temperature Monitor that is power by transformer stepping 480V-> 240V

Question 6

What’re the indications on the Electronic Temperature Monitor?

Answer 6

Green light: When AC power is available
Yellow light : lights up when fans are turned on (180 degrees Celsius )
Red Light : When temp. Reaches 200 degrees Celsius and will alarm control room

Question 7

What is the bell alarm switch for on 480VAC class load centers ?

Answer 7

It is to provide local indication that the breaker has tripped on overcurrent, white reset button must be reset to recluse breaker

Question 8

What’re the MCC interlocks built onto the class cabinet ?

Answer 8

Operating mechanism and compartment door are interlocked to prevent opening of the door while breaker is in “on” position

Question 9

Why is there disconnect switch’s on ‘B’ train ?

Answer 9

It’s to disconnect power from control room during a fire in control room

Question 10

What’re SIAS load shed centers for ?

Answer 10

During a LOCA the loads are not need so they’re tripped open from a SIAS signal to prevent generator from overload

Question 11

How do you override a SIAS load shed signal ?

Answer 11

You push trip button on load center breaker, then a white override light will come on indicating that the breaker can now be closed locally