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Power plant engineering: board exam questions with solutions

On the REE exam under Electrical Engineering Professional Subjects. Try each question before you open its solution, then practise with fresh numbers below: 2 computed question types on this topic.

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Questions

1. The load factor of a power plant over a period is defined as:

  1. Average load divided by peak (maximum) load
  2. Peak load divided by installed capacity
  3. Energy generated divided by installed capacity × hours
  4. Maximum demand divided by connected load
Show the answer and solution

Answer: A. Average load divided by peak (maximum) load

Load factor = average load/peak load for the same period. Energy over capacity × hours is the capacity factor, and maximum demand over connected load is the demand factor.

2. A plant generates 4800 kWh in a day and its peak load that day is 400 kW. What is the daily load factor?

  1. 83%
  2. 50%
  3. 12%
  4. 200%
Show the answer and solution

Answer: B. 50%

Average load = 4800/24 = 200 kW. Load factor = 200/400 = 0.50 = 50%.

3. A 100 MW plant produces 438 000 MWh in a (non-leap) year. What is its annual capacity factor?

  1. 44%
  2. 60%
  3. 50%
  4. 25%
Show the answer and solution

Answer: C. 50%

CF = energy/(capacity × hours) = 438 000/(100 × 8760) = 0.50 = 50%.

4. A thermal plant has a net heat rate of 10 000 kJ/kWh. What is its overall thermal efficiency?

  1. 10%
  2. 28%
  3. 100%
  4. 36%
Show the answer and solution

Answer: D. 36%

1 kWh = 3600 kJ, so η = 3600/heat rate = 3600/10 000 = 0.36 = 36%.

5. A 50 MW coal plant operates at full load with a heat rate of 11 000 kJ/kWh. The coal has a heating value of 25 000 kJ/kg. How much coal does it burn per hour?

  1. 22 t/h
  2. 114 t/h
  3. 7.2 t/h
  4. 2.2 t/h
Show the answer and solution

Answer: A. 22 t/h

Heat input = 50 000 kWh/h × 11 000 kJ/kWh = 5.5 × 10⁸ kJ/h. Coal = 5.5 × 10⁸/25 000 = 22000 kg/h = 22 t/h.

6. Which type of plant is best suited to serve short daily peak loads because it can start and reach full load quickly?

  1. Nuclear plant
  2. Open-cycle gas turbine plant
  3. Coal-fired steam plant
  4. Geothermal plant
Show the answer and solution

Answer: B. Open-cycle gas turbine plant

Open-cycle gas turbines start in minutes and have low capital cost, making them suitable for peaking duty. Nuclear, coal and geothermal plants are run as base load.

7. A building has a connected load of 500 kW and a measured maximum demand of 300 kW. What is the demand factor?

  1. 1.67
  2. 0.40
  3. 0.60
  4. 0.30
Show the answer and solution

Answer: C. 0.60

Demand factor = maximum demand/connected load = 300/500 = 0.60.

8. A hydro plant has a net head of 50 m, a flow of 20 m³/s, and an overall efficiency of 85%. What is its electrical output?

  1. 9.81 MW
  2. 7.09 MW
  3. 83.38 MW
  4. 8.34 MW
Show the answer and solution

Answer: D. 8.34 MW

P = ρ g Q H η = 1000 × 9.81 × 20 × 50 × 0.85 = 8338500 W ≈ 8.34 MW.

Worked examples with computed numbers

These numbers are fixed on this page; in practice they change every time.

9. A plant generates 6480 MWh in a 30-day month and its peak demand is 20 MW. What is its load factor?

  1. 45%
  2. 56.3%
  3. 22.2%
  4. 3.7%
Show the answer and solution

Answer: A. 45%

Average demand = 6480 MWh/(30 × 24 h) = 9 MW; load factor = average/peak = 9/20 = 45%.

10. A 100 W appliance runs 6 hours a day for 30 days at ₱11.5/kWh. What does it cost?

  1. ₱207
  2. ₱29.57
  3. ₱6.9
  4. ₱2070
Show the answer and solution

Answer: A. ₱207

100 W × 6 h × 30 days = 18 kWh; × ₱11.5 = ₱207.

Other topics in the same subjects

DC circuits · AC circuits · Three-phase systems · Transients (RC, RL, RLC) · Semiconductors and diodes · Power electronics · Instrumentation and measurement · Control systems · Transformers · DC machines · Induction motors · Synchronous machines · Power systems and transmission · Protection: fuses, breakers, relays · Illumination · PEC: branch circuits, ampacity and protection

An independent, free reviewer: not affiliated with the PRC or the Boards. Subject weights and passing rules are from the PRC examination programs and the laws (RA 9292, RA 7920); check the current PRC program before you file. Code questions follow the Philippine Electrical Code 2017 Part 1; check them against your own copy of the Code.