SOPD Voltage Regulation 2 — Questions and Answers
Question 1: A transmission line experiences a sudden load increase. What is the FIRST control action a system operator should take to restore voltage?
- Trip the overloaded line
- Dispatch reactive power from nearby generators or capacitor banks (Correct answer)
- Reduce active power generation
- Increase transformer turns ratio manually
Correct answer: Dispatch reactive power from nearby generators or capacitor banks
Reactive power support from generators or switched capacitor banks is the primary and fastest method to restore depressed voltage from load increases.
Question 2: What does a negative voltage regulation value indicate about a transmission line?
- The line is overloaded
- Receiving-end voltage is higher than sending-end voltage (Correct answer)
- Reactive power losses are excessive
- The line is operating below rated capacity
Correct answer: Receiving-end voltage is higher than sending-end voltage
Negative voltage regulation occurs on lightly loaded or capacitive lines where the Ferranti effect raises receiving-end voltage above the sending-end value.
Question 3: Which reactive power device provides continuously variable voltage support without introducing harmonics?
- Fixed shunt capacitor bank
- Mechanically switched reactor
- Static VAR Compensator (SVC) (Correct answer)
- Synchronous condenser
Correct answer: Static VAR Compensator (SVC)
An SVC uses thyristor-controlled reactors and thyristor-switched capacitors to provide stepless, rapid reactive power control with minimal harmonic injection (filters included).
Question 4: Under which condition is the Ferranti effect most pronounced on a high-voltage transmission line?
- Full load, lagging power factor
- Light load or open-circuit at the receiving end (Correct answer)
- Heavy inductive load at the receiving end
- Balanced three-phase fault at midpoint
Correct answer: Light load or open-circuit at the receiving end
The Ferranti effect is caused by line charging capacitance; with little or no load, there is no inductive current to offset the capacitive charging, so receiving-end voltage rises above sending-end voltage.
Question 5: A generator is operating at rated MW output. The operator increases excitation. What happens to the generator's reactive power output and terminal voltage?
- Reactive power decreases; terminal voltage drops
- Reactive power increases; terminal voltage tends to rise (Correct answer)
- Reactive power stays constant; terminal voltage rises
- Reactive power decreases; terminal voltage stays constant
Correct answer: Reactive power increases; terminal voltage tends to rise
Increasing field excitation raises internal EMF, which pushes more reactive power (MVAR) out of the generator and supports higher terminal voltage.
Question 6: What is the purpose of a load tap changer (LTC) deadband setting on a transformer?
- Prevents the transformer from energizing under fault conditions
- Avoids unnecessary tap operations for small voltage deviations within an acceptable range (Correct answer)
- Sets the maximum allowable tap position during peak load
- Limits fault current through the transformer windings
Correct answer: Avoids unnecessary tap operations for small voltage deviations within an acceptable range
The deadband prevents hunting (rapid repeated tap changes) by requiring voltage to deviate beyond a defined band before a tap operation is initiated.
Question 7: During a regional voltage emergency, the system operator issues a Conservative Operations instruction. Which of the following actions is consistent with that instruction?
- Increasing load transfers across the affected area
- Reducing voltage set points on generation to save fuel
- Arming additional reactive reserves and avoiding further reactive resource commitment (Correct answer)
- De-energizing all shunt reactors in the affected zone
Correct answer: Arming additional reactive reserves and avoiding further reactive resource commitment
Conservative Operations calls for preserving reactive reserves and limiting conditions that could worsen voltage collapse risk, including holding reactive resources in reserve.
SOPD Voltage Regulation 2
A transmission line experiences a sudden load increase.
What is the FIRST control action a system operator should take to restore voltage?