250+ TOP MCQs on Efficiencies in a Steam Power Plant – 2 and Answers

Power Plant Engineering Multiple Choice Questions on “Efficiencies in a Steam Power Plant – 2”.

1. The steam power plant is a bulk energy converter where fuel energy is converted to?
a) heat energy
b) electrical energy
c) chemical energy
d) none of the mentioned
Answer: b
Clarification: Energy conversion in a steam power plant is as below
Fuel energy to Electricity.

2. Rate of energy released by the combustion of the fuel is given by?
a) Fuel burning rate x Calorific Value of the fuel
b) Fuel burning rate / Calorific Value of the fuel
c) Fuel burning rate + Calorific Value of the fuel
d) Fuel burning rate – Calorific Value of the fuel
Answer: a
Clarification: Rate of energy released by the combustion of the fuel is given by,
Fuel burning rate x Calorific Value of the fuel.

3. The overall efficiency n_overall of a steam power plant is given by?
a) n_overall = (power available at the generator terminals / (Fuel burning rate x Calorific Value of the fuel))
b) n_overall = (power available at the generator terminals + (Fuel burning rate x Calorific Value of the fuel))
c) n_overall = (power available at the generator terminals – (Fuel burning rate x Calorific Value of the fuel))
d) none of the mentioned
Answer: a
Clarification: The overall efficiency n_overall of a steam power plant is given by,
n_overall = (power available at the generator terminals / (Fuel burning rate x Calorific Value of the fuel)).

4. Which of the following shows the correct relation? (n_boiler denotes efficiency of a boiler)
a) n_boiler = (rate of energy absorption by water to form steam / rate of energy released by the combustion of fuel)
b) n_boiler = (rate of energy absorption by water to form steam + rate of energy released by the combustion of fuel)
c) n_boiler = (rate of energy absorption by water to form steam – rate of energy released by the combustion of fuel)
d) n_boiler = (rate of energy absorption by water to form steam x rate of energy released by the combustion of fuel)
Answer: a
Clarification: The efficiency of a boiler is given by the following expression,
n_boiler = (rate of energy absorption by water to form steam / rate of energy released by the combustion of fuel).

5. The mechanical efficiency of a turbine is given by? (n_tm denotes the mechanical efficiency)
a) n_tm = (brake output of the turbine x internal output of the turbine)
b) n_tm = (internal output of the turbine / break output of the turbine)
c) n_tm = (brake output of the turbine / internal output of the turbine)
d) n_tm = (brake output of the turbine – internal output of the turbine)
Answer: c
Clarification: The expression for the turbine mechanical efficiency is given by,
n_tm = (brake output of the turbine / internal output of the turbine).

6. If Q₁ represents the rate of heat addition to the cycle and W_net represents net cycle work output, the expression for net cycle heat rate is?
a) Q₁ + W_net
b) Q₁ / W_net
c) Q₁ / (1/W_net)
d) Q₁ x W_net
Answer: b
Clarification: The expression for the net cycle heat rate is given by,
Net cycle heat rate(HR) = Q₁ / W_net.

7. The generator efficiency n of the electric alternator is?
a) n = (electrical output at generator terminals / Brake output of the turbine)
b) n = (electrical output at generator terminals x Brake output of the turbine)
c) n = (electrical output at generator terminals / (1/ Brake output of the turbine))
d) none of the mentioned
Answer: a
Clarification: The generator efficiency of the electric alternator is defined as the ratio of electrical output at generator terminals to the brake output of the turbine.

8. Which of these is not an auxiliary equipment in a power plant?
a) Fans
b) Crushers
c) Galvanisers
d) Conveyors
Answer: c
Clarification: The auxiliary equipment in a power plant are those equipment which are driven by the electricity taken from the generated power of the plant.

9. Which of these shows the formula for the efficiencies of the auxiliaries n₁?
a) n₁ = (net power transmitted by the generator x gross power produced by the plant)
b) n₁ = (net power transmitted by the generator / gross power input to the plant)
c) n₁ = (net power transmitted by the generator / gross power produced by the plant)
d) n₁ = (net power transmitted by the generator / gross power transferred by the plant)
Answer: c
Clarification: The auxiliary equipment or auxiliaries in a power plant are those equipment which are driven by the electricity taken from the generated power of the plant. Their efficiency is given by,
n₁ = (net power transmitted by the generator / gross power produced by the plant).

10. What approximate percentage of energy in the fuel is converted to electricity?
a) 55%
b) 45%
c) 35%
d) 25%
Answer: c
Clarification: Only 34% of the energy stored in the fuel is converted to electricity & 66% is lost. The maximum loss of energy takes place in the condenser where heat is rejected to cooling water.

11. Heat rejection in a condenser is to?
a) cooled water
b) coolant
c) cooling water
d) none of the mentioned
Answer: c
Clarification: The maximum loss of energy takes place in the condenser where heat is rejected to cooling water. This is the loss due to heat to work energy conversion in the cycle or the loss due to second law.

12. Heat rate indicates?
a) heat added per unit volume
b) heat added per unit of work produced
c) heat added per unit of mass stored
d) heat added per unit area
Answer: b
Clarification: The parameter which readily affects the fuel economy is the heat rate which is inversely proportional to the efficiency, and hence the lower its value the better. It broadly indicates the heat added per unit of work produced.

13. Which of the following parameters affects the fuel economy?
a) heat constant
b) specific heat
c) heat rate
d) heat consumption
Answer: c
Clarification: The parameter which readily affects the fuel economy is the heat rate which is inversely proportional to the efficiency, and hence the lower its value the better. It broadly indicates the heat added per unit of work produced.

14. Gross cycle heat rate is equal to?
a) (rate of heat addition / turbine output)
b) (rate of heat rejection / turbine input)
c) (heat rejected / turbine output)
d) none of the mentioned
Answer: a
Clarification: The gross cycle heat rate is given by,
Gross cycle heat rate = (rate of heat addition / turbine output).

15. The relation between heat rate & efficiency is?
a) both are directly proportional
b) both are inversely proportional
c) they are independent of each other
d) heat rate is also called efficiency
Answer: b
Clarification: The parameter which readily affects the fuel economy is the heat rate which is inversely proportional to the efficiency, and hence the lower its value the better. It broadly indicates the heat added per unit of work produced.