Power Systems Questions and Answers – Efficiency of Steam Power Plant

This set of Power Systems Multiple Choice Questions & Answers (MCQs) focuses on “Efficiency of Steam Power Plant”.

1. Which part of thermal power plant causes maximum energy losses?
a) Boiler
b) Alternator
c) Condenser
d) Ash and unburnt carbon

Explanation: About 54% of energy losses occurs in condenser. Losses in boiler and alternator are about 1% and 16% because of such high losses overall efficiency of thermal power plant reduces to 29% for normal old thermal power plant and 50% for modern super critical pressure steam power plant which employs many heat saving devices.

2. What is the effect of increasing steam pressure on efficiency of steam power plant?
a) Increases linearly
b) Increases nonlinearly
c) Decreases linearly
d) Does not changes

Explanation: The thermal efficiency of steam power plant depends upon the steam pressure. The efficiency increases with increasing steam pressure nonlinearly up to a level. After that level increase in efficiency becomes very low with respect to increasing pressure.

3. What is the effect of increasing steam temperature of thermal power plant on its thermal efficiency?
a) Increases linearly
b) Decreases
c) It does not depends on temperature
d) Increases nonlinearly

Explanation: Thermal efficiency of steam power plant increases with increase in steam temperature linearly. Increas in temperature of steam also causes its effect on cost. So temperature of steam is increased only upto a level at which it is economical.

4. Overall efficiency of thermal power plant is equal to ___________
a) Thermal efficiency
b) Generation efficiency
c) Multiplication of thermal and generation efficiency
d) Ratio of thermal and generation efficiency

Explanation: Thermal efficiency of steam power plant is the ratio of the heat equivalent of mechanical energy transmitted to the turbine shaft and the heat of the combustion. Thermal efficiency is generally quite low about 30%. Efficiency of generator is called generation efficiency.

5. In supercritical pressure steam power plant temperature of steam is __________
a) 480°C
b) 240°C
c) 600°C
d) 150°C

Explanation: At a temperature about 600°C water enters in supercritical phase and has property between those of liquid and gas. advantage of such plant are that low grade fossil fuel (lignite) can be used. Efficiency of such plants may be reached up to 50%.

6. For increasing the thermal efficiency of thermal power plant pressure in condenser should be:
a) Reduced upto 0.04 kg/cm2
b) Kept above 2.45 kg/cm2
c) As high as boiler pressure
d) Same as atmospheric pressure

Explanation: The thermal efficiency can be effectively increased by decreasing the pressure in the condenser. Pressure in condenser is kept very low usually 0.04 kg/cm2 .

7. Economisers are necessary to use for pressure of 70 kg/cm2 or more.
a) True
b) False

Explanation: High cost of fuel consumption, high load factor and high pressure and temperature conditions, all justify the use of economiser. Installation of economiser involves extra cost of installation, maintenance and regular cleaning and additional requirement of space. By considering above points it has been found that use of economiser becomes necessary for pressure above 70 kg/cm2.

8. Supercritical pressure boiler scan produce steam at the rate of _________
a) less than 1,500 kg/hr
b) less than 340,000 kg/hr
c) less than 80,000 kg/hr
d) upto 1,000,000 kg/hr

Explanation: Modern supercritical pressure boiler with pressures as high as 350 atm temperature 600°C and capacity 1,000,000 kg/hour are available now days. Fire tube boiler can produce steam at the rate of 15,000 kg/hr. Water tube boiler can produce 340,000 kg of steam per hour.

Sanfoundry Global Education & Learning Series – Power Systems.