SOPD Voltage Control & System Reliability 4

Question 1

An operator notices that reactive power is flowing FROM the high-voltage transmission system INTO a generator's stator. What does this indicate?

Accepted Answer

The generator is under-excited and absorbing reactive power from the system

Answer

When reactive power flows into a generator, the machine is operating under-excited (absorbing VARs), which can risk loss of synchronism at the generator's stability limit.

Question 2

Which condition is most likely to cause a cascading voltage collapse on an interconnected power system?

Accepted Answer

Multiple contingencies depleting reactive reserves faster than they can be restored

Answer

Cascading voltage collapse typically results from successive contingencies that cumulatively exhaust reactive reserves, leaving no margin to sustain voltage.

Question 3

What is 'reactive power zoning' in the context of voltage control?

Accepted Answer

Dividing the grid into areas where reactive power flow between zones is minimized to keep reactive support local

Answer

Reactive power zoning partitions the system into areas to minimize long-distance reactive transfer, since reactive power is best controlled locally to avoid excessive losses.

Question 4

A system operator is directed to maintain a 5% reactive reserve margin. If total reactive capability is 2,000 MVAR, what is the minimum reactive reserve required?

Accepted Answer

100 MVAR

Answer

5% of 2,000 MVAR = 100 MVAR minimum reactive reserve required to maintain the specified margin.

Question 5

Which generator parameter directly limits the maximum reactive power (leading) that a synchronous generator can absorb?

Accepted Answer

Minimum excitation limit (under-excitation limiter)

Answer

The under-excitation limiter (UEL) protects the generator from operating too far under-excited, which risks loss of synchronism due to insufficient rotor field current.

(SOPD) System Operator/Power Dispatching Practice Test

(SOPD) System Operator/Power Dispatching Practice Test

SOPD Voltage Control & System Reliability 4