Voltage Control & System Reliability Flashcards
7 cards from real SOPD practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Voltage Control & System Reliability flashcards as text
An operator notices that reactive power is flowing FROM the high-voltage transmission system INTO a generator's stator. What does this indicate?
Answer: The generator is under-excited and absorbing reactive power from the system
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.
Which condition is most likely to cause a cascading voltage collapse on an interconnected power system?
Answer: Multiple contingencies depleting reactive reserves faster than they can be restored
Cascading voltage collapse typically results from successive contingencies that cumulatively exhaust reactive reserves, leaving no margin to sustain voltage.
What is 'reactive power zoning' in the context of voltage control?
Answer: Dividing the grid into areas where reactive power flow between zones is minimized to keep reactive support local
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.
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?
Answer: 100 MVAR
5% of 2,000 MVAR = 100 MVAR minimum reactive reserve required to maintain the specified margin.
Which generator parameter directly limits the maximum reactive power (leading) that a synchronous generator can absorb?
Answer: Minimum excitation limit (under-excitation limiter)
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.
During a voltage emergency, a Transmission Operator issues a Transmission Emergency instruction to reduce load. Under NERC EOP-011, this action is considered:
Answer: A mandatory directive that the Balancing Authority must follow
NERC EOP-011 establishes that emergency operating instructions issued by the TOP must be followed by the Balancing Authority to mitigate reliability emergencies.
What is the voltage effect of energizing a long, unloaded 345 kV transmission line?
Answer: The receiving-end voltage rises above sending-end voltage due to the Ferranti effect
The Ferranti effect causes the receiving-end voltage of an open-circuited (unloaded) line to rise above the sending-end voltage due to distributed line capacitance.