MCQs on Power Systems

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01․ Reheat cycle in thermal power plant is used to
reduce loss of heat.
utilize heat of flue gases.
increase thermal efficiency.
improve condenser performance.

In the reheat cycle, the steam, is extracted from the suitable point in the turbine and is reheated with the help of the flue gases in the boiler furnace. The main purpose of reheating is to increase the dryness of the steam of passing through lower stages of the turbine. The increase in the thermal efficiency due to the reheat depends upon the thermal efficiency due to the reheat depends upon the ratio of reheat pressure to original pressure steam.

02․ Maximum efficiency of modern coal fired steam raising thermal power plants is restricted to about 035 (a low value), mainly because of
low steam turbine mechanical efficiency.
high energy loss in boiler.
low alternative efficiency.
high energy loss from turbine exhaust to condenser.

Overall efficiency is depends on turbine boiler and alternator efficiency. When the steam is entering the turbine, then heat rejected to the condenser and this loss is unavoidable as heat energy cannot be converter into mechanical energy without drop in temperature.

03․ The modern trend in electric power generation
to have large size thermal plant located near coal fields.
to have large number of small size thermal plants located at different places.
to have large size thermal plants near load centre.
none of above.

The steam power plant is located near the coal fields in order to reduce the transportation charges. In case the plant is located near a coal pit, transportation cost by rail, road, sea or river is avoided. If a coal mine is very near, sometimes aerial rope ways are employed to carry coal to the site. Thus the generating cost is reduced. Thereby the modern trend in electric power generation is to have large size thermal plant located near coal fields.

04․ Deaerative heating is done to
heat the feed water.
heat the steam.
remove dissolved.
remove dissolved gases in water.

The steam coming out of the turbine is condensed and the condensate is extracted from the condenser by the condensate extraction pump and is forced to low pressure feed water heater where its temperature is raised by the heat from bled steam (extracted from the lowest pressure extraction point of turbine). Then the feed water is pumped through deaerator to high pressure heaters. The function of deaerative heating is to reduce the dissolved oxygen.

05․ In a steam power plant, the feed water coming to the economizer is heated plant the feed water coming to the economizer is heated using
HP steam.
flue gas.
LP steam.
direct heat in the furnace.

The feed water is pumped into boiler through economizer in which it is further heated by the heat of flue gases passing through it on the way to chimney.

06․ Pipes carrying steam are generally of
cast iron.

Generally steam pipe are made of steel.

07․ Carnot cycle comprises of
two isentropic process and two constant pressure process.
two isentropic process and two constant volume process.
two isothermal process and two constant pressure process.
none of above.

The Carnot cycle is thermodynamic cycle that can be shown the most efficient cycle for converting a given amount of thermal energy into work pressure of system is constant.

08․ Which of following power plants is free from environmental problem
Diesel engine.

In hydroelectric power plant, there is not combustion of coal or diesel and no problem of handling and disposal of ash. It is very neat and clean because no smoke or ash is produced. It is not needed nuclear fission process. For this reason, hydroelectric plant is free from environmental problem.

09․ Gas turbine power plants for maximum efficient may have
Heat exchangers.
Multistage compression.
All of above.

The reheating uitilize the heat of exhaust gases to heat the compressed air before it is sent to the combustion chamber, reduces the fuel consumption of the plant and improve efficeiency to maximum. For multistage compression, the inlet temeperature of turbine and pressure rate increases, the heat supplied as well as the heat heat rejected are reduce. But the rate of change of heat supplied as well as the heat supplied is not same as the rate of change heat rejected. As a consequence, there exist an otimum pressure ratio producting maximum efficiency for a given turbine inlet temperature.

10․ Which of the following plants has the maximum eapital cost
Diesel plants.
Nuclear plants.
Steam plants.

Nuclear plans need very high capital because of huge investment on building a nuclear reactor.