A steam power plant belongs to a class of power plants that generate electrical power from the heat energy of coal combustion. Like any other power plant, on the bigger picture components of the steam power plant are a prime move, an alternator, and a source for turning the prime mover. Electrical Engineering Online shares the top 10 most important Multiple Choice Questions on Steam Power plants with brief explanatory answers.
Also see: Complete list of Electrical Engineering Online MCQ Questions
Coal is Pulverised in the coal and ash handling section so as to
Coal is Pulverised in the coal and ash handling section so as to:
- Increase the surface exposure
- Allow rapid combustion of coal
- Carry combustion process in a small quantity of air
- All of above
Correct answer: 4. All of above
Explanation: The term pulverization in reference to coal power stations implies the crushing of coal into smaller pieces. In a steam power station, coal is not directly used, rather it is pulverized into smaller pieces. Such a practice provides three major benefits. It increases the surface exposure of coal while allowing the rapid combustion process in a limited amount of air.
In the case of Steam Turbines, the Reheat factor is dependent on which of following factors
In the case of Steam Turbines, the Reheat factor is dependent on which of the following factors:
- Exit pressure only
- Initial pressures and temperature
- Stage efficiency only
- All of above
Correct answer: 2. Initial pressures and temperature
Explanation: By definition, the reheat factor is defined as the ratio of the cumulative heat to the adiabatic drop from the initial condition to exhaust pressure. The reheat factor of steam turbines is dependent on Initial pressures and temperature.
Superheater employed in Steam Power Plants has a major advantage that
Superheater employed in Steam Power Plants has a major advantage that:
- It boosts the overall efficiency of the power plant
- Condensation is reduced
- It increases the life of blades
- All of these
Correct answer: 4. All of these
Explanation: The superheater in steam power station is used for raising the temperature of steam generated in the boiler. As a result of superheating the overall efficiency of is increased. Apart from an increase in overall efficiency, the condensation in the last stages of turbine is reduced which could have been too much in case of absence of a superheater. Another major advantage linked with the reduction of condensation is the aversion to blade corroision. As a result of reduction in condensation the life of blades inturn increases.
Steam turbines normally used in steam power stations are of
Steam turbines normally used in steam power stations are of
- Condensing type
- Non-condensing type
- Both of these
- None of these
Correct answer: 1. Condensing type
Explanation: Steam turbines are generally categorized into two types, which include condensing and noncondensing type turbines. Condensing type of steam turbines are flexible turbines wherein the output can be regulated as per the requirement, and these can be employed for the generation of bulk amounts of electricity.
The major disadvantage associated with a non-condensing turbine that discourages its use is its inflexibility to meet the demand of variable loads.
The effect of considering friction in steam nozzles for same pressure ratio leads to
The effect of considering friction in steam nozzles for same pressure ratio leads to
- Decrease in dryness fraction of exit steam
- Decrease or increase of dryness fraction of exit steam depending upon inlet quality
- Increase in dryness fraction of exit steam
- No change in the quality of exit steam
Correct answer: 3. Increase in dryness fraction of exit steam
Rankine cycle efficiency of a good steam power plant may be in the range of
Rankine cycle efficiency of a good steam power plant may be in the range of
- 15 to 19.3 percent
- 35.8 to 42 percent
- 69.52 to 78.6 percent
- 90.2 to 95 percent
Correct answer: 2. 35.8 to 42 percent
Example: The working principle of the steam power station is based on the Rankine cycle. The efficiency of the Rankine cycle is reduced because of the high heat of vaporization of working fluid and the Ranking cycle efficiency of good steam power plants can be in the range of 35.8 to 42 percent.
Steam expands completely in stationery nozzles in case of which type of turbine
Steam expands completely in stationery nozzles in case of which type of turbine
- Impulse turbines
- Impulse-reaction turbines
- Reaction turbines
- None of these
Correct answer: 1. Impulse turbines
Explanation:
Steam turbines are broadly classified into two types. This classification is based on the action of steam on moving blades. The two types are known as impulse turbines and reaction turbines. In the case of impulse turbines steam expands completely in stationary nozzles. While on the other hand, in the case of a reaction turbine, steam is partially expanded in the stationary nozzles. The remaining expansion occurs while steam is passing over the moving blades.
Economizer in steam power plants improve boiler efficiency as much as
Economizers in steam power plants improve boiler efficiency as much as
- 1 to 5%
- 10 to 12%
- 4 to 10%
- 8 to 12%
Correct answer: 3. 4 to 10%
The boiler efficiency and turbine efficiency of a thermal power station is 87% and 89% respectively. The thermal efficiency of station will be
The boiler efficiency and turbine efficiency of a thermal power station is 87% and 89% respectively. The thermal efficiency of station will be:
- 88.5%
- 77.43%
- 89.87%
- 72.33%
Correct answer: 2. 77.43%
Explanation:
From the formula: Thermal Efficiency = Boiler Efficiency * Turbine Efficiency
Thermal Efficiency = 0.87 * 0.89 = 0.7743 = 77.43%
Softening of Water in Steam Power Plant
One of the parts of modern steam power plants is the water treatment plant. The purpose of such a plant is to soften the water which is vital for the longer life of the plant. The aforementioned statement is:
- Correct
- Incorrect
Correct answer: 1. Correct
Explanation: One of the most important parts of the steam power plant is the water treatment portion. The boiler of a steam power plant requires clean water for the long life of the plant. The boiler feed water is obtained from rivers and usually, it has impurities. If such water is directly fed to the boiler it will reduce efficiency as well as will reduce the useful life span of the boiler. If is therefore purified and then softened by removing hardness in water.