Free Power Systems MCQs with Answers
334 Power Systems MCQs from Electrical Engineering, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
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334 questions · page 8 of 17
- A. increased business activity
- B. increased water supply
- C. increased use of fans and air conditioners
- D. none of the above
Explanation: Summer demand rises mainly because fans and air conditioners operate more frequently and for longer periods.
Correct answer: increased use of fans and air conditioners- A. Steam
- B. Diesel
- C. Hydroelectric
- D. Any of the above
Explanation: Hydroelectric plants usually have the longest service life because their main civil structures, such as dams and waterways, can remain…
Correct answer: Hydroelectric- A. fuel cells
- B. solar cells
- C. MHD generators
- D. none of the above
Explanation: An MHD generator converts the thermal energy of a hot, electrically conducting gas directly into electricity without an intermediate…
Correct answer: MHD generators- A. arc lamps
- B. induction motors
- C. fluorescent tubes
- D. incandescent lamp
Explanation: An incandescent lamp is mainly a resistive load, so its current and voltage are nearly in phase and its power factor is close to unity.
Correct answer: incandescent lamp- A. plant is used for stand by purpose only
- B. plant is under maintenance
- C. plant is used for base load only
- D. plant is used for peak load as well as base load
Explanation: Utilization factor is the ratio of maximum demand to plant capacity. A low value means much of the installed capacity remains unused, as…
Correct answer: plant is used for stand by purpose only- A. total installed capacity of the plant
- B. sizes of the generating units
- C. operating schedule of generating units
- D. all of the above
Explanation: A load curve shows demand variation with time, so it determines the required installed capacity, suitable generating-unit sizes, and their…
Correct answer: all of the above- A. sinking fund depreciation
- B. straight line depreciation
- C. reducing balances depreciation
- D. none of the above
Explanation: Under reducing-balance depreciation, the annual depreciation is calculated as a fixed percentage of the plant's diminishing book value, so…
Correct answer: reducing balances depreciation- A. zero slope
- B. positive slope
- C. negative slope
- D. All of these
Explanation: A load curve may rise, fall, or remain constant over different time intervals, giving positive, negative, or zero slope.
Correct answer: All of these- A. operating schedule of generating units
- B. sizes of generating units
- C. total installed capacity of the plant
- D. all of the above
Explanation: The load curve provides both the magnitude and time variation of demand, allowing engineers to select plant capacity, unit sizes, and the…
Correct answer: all of the above- A. fixed cost of unit generated
- B. running cost of unit generated
- C. both A. and B.
- D. neither A. nor B.
Explanation: A higher diversity factor reduces the combined maximum demand compared with the sum of individual demands, lowering required plant…
Correct answer: fixed cost of unit generated- A. average demand
- B. energy consumed
- C. maximum demand
- D. none of the above
Explanation: The area under a load-versus-time curve is load multiplied by time, which gives electrical energy consumed, usually in kWh.
Correct answer: energy consumed- A. 10 to 15%
- B. 30 to 40%
- C. 50 to 60%
- D. 60 to 70%
Explanation: Domestic appliances are used intermittently and their combined maximum demand is much higher than their average demand, so domestic load…
Correct answer: 10 to 15%- A. 15 years
- B. 30 years
- C. 60 years
- D. 100 years
Explanation: Hydroelectric stations have very long service lives because their turbines, generators and civil structures are robust and can be…
Correct answer: 100 years- A. Direct stroke on line conductor
- B. Indirect stroke on conductor
- C. Direct stroke on tower top
- D. Direct stroke on ground wire
Explanation: A direct stroke to a line conductor injects the lightning current directly into the electrical circuit, producing severe overvoltages and…
Correct answer: Direct stroke on line conductor- A. Easily damaged by high voltage
- B. Cannot be repaired
- C. Short service life
- D. All of the above
Explanation: Static capacitors can be damaged by overvoltage, and an individual unit is normally replaced rather than repaired; their service life is…
Correct answer: All of the above- A. peak load plant
- B. casual run plant
- C. either A. or (b)
- D. base load plant
Explanation: Efficiency matters least for a peak-load or casual-run plant because it operates for relatively few hours.
Correct answer: either A. or (b)157. The primary reason for low power factor is supply system is due to installation of____________?
- A. induction motors
- B. synchronous motors
- C. single phase motors
- D. d.c. motors
Explanation: Induction motors draw magnetising current and therefore consume substantial reactive power, causing a lagging power factor in supply…
Correct answer: induction motors- A. peak demand
- B. average demand
- C. diversified demand
- D. none of the above
Explanation: A load curve plots demand against time, so its highest ordinate is the maximum or peak demand reached during the period.
Correct answer: peak demand- A. peak load plants
- B. base load plants
- C. either A. or (b)
- D. none of the above
Explanation: Base-load plants operate for long periods, so their high capital cost is spread over many generated units and their superior efficiency…
Correct answer: base load plants- A. 25 to 50 percent full load
- B. 50 to 75 percent full load
- C. full load
- D. 25 percent overload
Explanation: Peak-load generators commonly achieve maximum efficiency below full load, typically around 50 to 75 percent of rated load.
Correct answer: 50 to 75 percent full load