SOPD Voltage Control & System Reliability 2 — Questions and Answers
Question 1: A system operator observes a sudden voltage collapse on a transmission corridor. What is the FIRST corrective action to take?
- Shed load in the affected area
- Trip the transmission line to isolate the fault
- Insert reactive power support such as capacitor banks or SVCs (Correct answer)
- Reduce active power generation on all units
Correct answer: Insert reactive power support such as capacitor banks or SVCs
Voltage collapse is primarily a reactive power deficiency; inserting reactive support (capacitor banks, SVCs) is the first corrective action.
Question 2: What does the term 'voltage stability margin' represent in power system operations?
- The difference between current voltage and the emergency low-voltage limit
- The distance in MW or MVAR loading from the current operating point to the voltage collapse point (Correct answer)
- The amount of reactive reserve available on generators
- The voltage deviation from nominal expressed as a percentage
Correct answer: The distance in MW or MVAR loading from the current operating point to the voltage collapse point
Voltage stability margin is the MW or MVAR distance from the current operating point to the nose point (collapse point) on the P-V or Q-V curve.
Question 3: Under NERC Reliability Standards, which entity is primarily responsible for maintaining voltage within acceptable limits on the bulk electric system?
- Balancing Authority
- Transmission Operator (TOP) (Correct answer)
- Distribution Provider
- Resource Coordinator
Correct answer: Transmission Operator (TOP)
The Transmission Operator (TOP) is responsible for maintaining transmission voltages within limits specified in their Operating Procedures.
Question 4: A generator is operating at rated MVA with a lagging power factor. To raise terminal voltage, the operator should:
- Decrease field excitation
- Increase field excitation (Correct answer)
- Reduce active power output
- Open the generator breaker
Correct answer: Increase field excitation
Increasing field excitation raises the generator's internal EMF, which increases terminal voltage and causes the machine to supply more reactive power.
Question 5: Which phenomenon describes a situation where voltage actually rises as load increases, indicating a potential instability condition?
- Ferroresonance
- Voltage inversion (Correct answer)
- Load tap changer (LTC) hunting
- Capacitive overcompensation
Correct answer: Voltage inversion
Voltage inversion occurs when a lightly loaded long line with shunt capacitance raises receiving-end voltage above sending-end voltage, indicating an unstable operating region.
Question 6: What is the primary purpose of a Static Var Compensator (SVC) in voltage control?
- To regulate active power flow on a transmission line
- To provide fast-acting continuous reactive power support to maintain bus voltage (Correct answer)
- To protect transmission lines from overvoltage during switching
- To reduce harmonic distortion in the power system
Correct answer: To provide fast-acting continuous reactive power support to maintain bus voltage
An SVC provides fast, continuous reactive power compensation (capacitive or inductive) to regulate bus voltage dynamically.
Question 7: During a high-load summer afternoon, reactive reserves are critically low. Which action would MOST effectively restore reactive reserve margin?
- Reduce transmission line loading by rescheduling generation
- Switch in shunt capacitor banks and bring additional generators online for reactive support (Correct answer)
- Increase transformer tap positions to raise voltage
- Reduce load through voluntary conservation requests only
Correct answer: Switch in shunt capacitor banks and bring additional generators online for reactive support
Energizing shunt capacitors and bringing reactive-capable generators online directly increases available reactive reserve to prevent voltage collapse.
SOPD Voltage Control & System Reliability 2
A system operator observes a sudden voltage collapse on a transmission corridor.
What is the FIRST corrective action to take?