BEE Power System 2 — Questions and Answers
Question 1: What is the purpose of a surge arrester in a power system?
- To regulate voltage frequency
- To protect equipment from transient overvoltages (Correct answer)
- To increase power factor
- To reduce line resistance
Correct answer: To protect equipment from transient overvoltages
Surge arresters clamp transient overvoltages caused by lightning or switching surges, protecting insulation of connected equipment.
Question 2: Which fault type is the most common in overhead transmission lines?
- Three-phase balanced fault
- Line-to-line fault
- Single line-to-ground fault (Correct answer)
- Double line-to-ground fault
Correct answer: Single line-to-ground fault
Single line-to-ground faults account for approximately 70–80% of all faults on overhead transmission lines due to insulator flashovers or conductor contact with ground.
Question 3: What does the term 'infinite bus' represent in power system analysis?
- A bus with zero impedance to ground
- A bus with constant voltage and frequency regardless of load (Correct answer)
- A bus with maximum short-circuit capacity
- A bus connected to multiple generators
Correct answer: A bus with constant voltage and frequency regardless of load
An infinite bus is an idealized source with constant voltage magnitude and frequency, used as a reference in stability studies.
Question 4: The Ferranti effect in a transmission line occurs when:
- The line is heavily loaded
- The line is lightly loaded or open-circuited at the receiving end (Correct answer)
- The line operates at leading power factor
- Harmonics exceed the fundamental frequency
Correct answer: The line is lightly loaded or open-circuited at the receiving end
Under light or no-load conditions, the charging current of the line causes the receiving-end voltage to exceed the sending-end voltage.
Question 5: In a power system, the term 'spinning reserve' refers to:
- Generators that are shut down but can start quickly
- Generating capacity online and synchronized but not fully loaded (Correct answer)
- Excess reactive power available in the system
- Transformer tap positions held in reserve
Correct answer: Generating capacity online and synchronized but not fully loaded
Spinning reserve is online generating capacity that can immediately respond to sudden load increases or generation loss.
Question 6: What is the skin effect in transmission line conductors?
- Increase in conductor resistance at high frequencies due to current crowding near the surface (Correct answer)
- Reduction of insulation resistance with temperature
- Increase in capacitance between conductors
- Corona discharge along the conductor surface
Correct answer: Increase in conductor resistance at high frequencies due to current crowding near the surface
At higher frequencies, eddy currents push current toward the conductor surface, effectively reducing the cross-sectional area and increasing resistance.
Question 7: The base impedance in a per-unit system is defined as:
- Base voltage divided by base current
- Base power multiplied by base voltage
- Base current multiplied by base power
- Base voltage squared divided by base MVA (Correct answer)
Correct answer: Base voltage squared divided by base MVA
Base impedance equals (base kV)² / base MVA, derived from Ohm's law applied to the chosen base voltage and power.
BEE Power System 2
What is the purpose of a surge arrester in a power system?