BEE FREE Bachelor of Electrical Engineering Power System Questions and Answers 2 — Questions and Answers
Question 1: What is the primary purpose of a bus bar in a power system substation?
- To collect and distribute electrical power to multiple circuits (Correct answer)
- To convert AC power to DC power
- To store electrical energy during peak demand
- To regulate voltage at the consumer end
Correct answer: To collect and distribute electrical power to multiple circuits
A bus bar serves as a common electrical junction point that collects power from incoming feeders and distributes it to outgoing feeders in a substation.
Question 2: In a three-phase power system, what happens to the line voltage relative to the phase voltage in a delta-connected generator?
- Line voltage equals phase voltage (Correct answer)
- Line voltage is √3 times phase voltage
- Line voltage is half the phase voltage
- Line voltage is twice the phase voltage
Correct answer: Line voltage equals phase voltage
In a delta connection, each line is connected across one phase winding, so the line voltage equals the phase voltage.
Question 3: Which type of fault in a power system is generally the most severe in terms of fault current magnitude?
- Three-phase symmetrical fault (Correct answer)
- Single line-to-ground fault
- Line-to-line fault
- Double line-to-ground fault
Correct answer: Three-phase symmetrical fault
A three-phase symmetrical fault produces the highest fault current because all three phases are short-circuited simultaneously, presenting the lowest impedance path.
Question 4: What does the term 'power factor correction' primarily aim to achieve in an industrial power system?
- Reduce reactive power demand and minimize current drawn from the supply (Correct answer)
- Increase the total active power consumed by loads
- Eliminate harmonic distortion in the supply voltage
- Boost the supply voltage at the point of common coupling
Correct answer: Reduce reactive power demand and minimize current drawn from the supply
Power factor correction reduces reactive power demand by adding capacitors or synchronous condensers, thereby minimizing the current drawn for the same active power load.
Question 5: In the per-unit system used for power system analysis, what is the per-unit value of a quantity equal to its base value?
- 1.0 per unit (Correct answer)
- 0 per unit
- 100 per unit
- It depends on the system voltage level
Correct answer: 1.0 per unit
By definition, when a quantity equals its chosen base value, the per-unit representation is exactly 1.0.
Question 6: What is the main advantage of using HVDC transmission over HVAC for very long distance power transfer?
- Lower transmission losses due to absence of reactive power losses and skin effect (Correct answer)
- Easier voltage transformation at substations
- Simpler protection and switchgear requirements
- Lower initial installation cost for all distances
Correct answer: Lower transmission losses due to absence of reactive power losses and skin effect
HVDC transmission eliminates reactive power losses and skin effect present in AC systems, making it more efficient for very long distance power transfer.
BEE FREE Bachelor of Electrical Engineering Power System Questions and Answers 2
What is the primary purpose of a bus bar in a power system substation?