BEE BEE Bachelor of Electrical Engineering Power Systems Engineering Questions and Answers 2 — Questions and Answers
Question 1: A 345 kV transmission line has a surge impedance of 400 ohms. What is the surge impedance loading (SIL) of the line?
- 297.6 MW (Correct answer)
- 172.5 MW
- 400 MW
- 245.3 MW
Correct answer: 297.6 MW
SIL equals V² divided by the surge impedance, so (345,000)² / 400 = 297.6 MW.
Question 2: In a power system, what is the primary purpose of a bus coupler breaker?
- To transfer load between two bus sections without interruption (Correct answer)
- To protect transformers from overvoltage
- To isolate faulty generators
- To regulate voltage at the distribution level
Correct answer: To transfer load between two bus sections without interruption
A bus coupler breaker connects two bus sections and allows load transfer between them without service interruption.
Question 3: Which type of fault in a three-phase power system typically produces the highest fault current?
- Three-phase bolted fault (Correct answer)
- Single line-to-ground fault
- Line-to-line fault
- Double line-to-ground fault
Correct answer: Three-phase bolted fault
A three-phase bolted fault produces the highest symmetrical fault current because it has the lowest impedance path.
Question 4: What does the equal area criterion determine in power system transient stability analysis?
- Whether a synchronous machine will remain in synchronism after a disturbance (Correct answer)
- The steady-state power transfer limit of a transmission line
- The optimal load dispatch between generators
- The voltage regulation of a transformer under load
Correct answer: Whether a synchronous machine will remain in synchronism after a disturbance
The equal area criterion compares accelerating and decelerating energy areas on the power-angle curve to determine if a generator maintains synchronism.
Question 5: A generator has a transient reactance of 0.25 per unit and delivers 1.0 per unit power at unity power factor. What is the internal voltage behind transient reactance?
- 1.03 per unit (Correct answer)
- 1.25 per unit
- 0.75 per unit
- 1.50 per unit
Correct answer: 1.03 per unit
The internal voltage is calculated as √(Vt² + (Xd'·I)²) = √(1² + 0.25²) ≈ 1.03 per unit at unity power factor.
Question 6: In economic load dispatch, what condition must be satisfied for optimal generation allocation among multiple units?
- The incremental cost of all participating units must be equal (Correct answer)
- Each unit must operate at its maximum efficiency point
- Total generation must equal total losses
- All units must share load equally
Correct answer: The incremental cost of all participating units must be equal
Optimal economic dispatch requires that all generating units operate at the same incremental fuel cost (lambda).
BEE BEE Bachelor of Electrical Engineering Power Systems Engineering Questions and Answers 2
A 345 kV transmission line has a surge impedance of 400 ohms.
What is the surge impedance loading (SIL) of the line?