NC RfG

Question 1

Req’d ROCOF of STG.

Answer 1

2 Hz/sec

Question 2

FRT for 0% voltage

Answer 2

150 msec

Question 3

FRT for 50% voltage

Answer 3

450 msec

Question 4

FRT for 85% voltage

Answer 4

1.5 sec

Question 5

Is there any difference between FRT for symmetrical vs asymmetrical faults?

Answer 5

No

Question 6

What is the basis for 150 msec fault clearing time?

Answer 6

Entsoe Implementation Guideline

Question 7

What is the basis for 250 msec clearance time?

Answer 7

150 mesc Entsoe guideline and assuming a breaker failure.

Question 8

How does the PLU work?

Answer 8

Difference between turbine exhaust steam pressure and generator current. > setpoint, it closes the steam valves to prevent overspeed.

Question 9

What is the meaning of Critical Fault Clearing Time?

Answer 9

Clearing time during which the generator is not out-of-step (i.e. - it’s OK)

Question 10

How does Critical FCT vary with grid SC availability?

Answer 10

Lower SC = lower critical FCT.

Question 11

IEC standard continuous allowable frequency variation?

Answer 11

+ / - 2% = 49 to 51 Hz

Question 12

What is the POI voltage range?

Answer 12

87.5% to 110%

Question 13

Does Poland AP1000 have to abide by 250 Msec FCT?

Answer 13

According to the NCRfG, it is only 150 msec.