Free Power Systems MCQs with Answers

• A. reduce the flame length
• B. increase the flame length
• C. transport and dry the coal
• D. provide air around burners for get¬ting optimum combustion

Explanation: Primary air carries pulverised coal from the mill to the burners and also dries it during transport.

• A. burn completely
• B. burn freely
• C. do not form ash
• D. form lumps or masses of coke

Explanation: Caking coal softens and fuses when heated, producing coherent lumps or masses of coke.

• A. 20 to 100 MW
• B. 50 to 300 MW
• C. 70 to 400 MW
• D. 100 to 650 MW

Explanation: In the conventional classification used for power-station equipment, large turbo-generators generally have ratings from about 50 to 300…

• A. 1 to 5%
• B. 4 to 10%
• C. 10 to 12%

Explanation: An economiser transfers heat from boiler flue gases to the feedwater, reducing the fuel required to produce steam.

• A. 20 kgf/cm2
• B. 50 kgf/cm2
• C. 100 kgf/cm2
• D. 150 kgf/cm2

Explanation: Modern steam-station boilers operate at high pressures, commonly of the order of 150 kgf/cm² in the textbook context of this question.

• A. center of coal fields
• B. center of maximum load of equipments
• C. center of gravity of electrical system

Explanation: The load centre is the electrical equivalent of the centre of gravity of the system, determined from the distribution of loads.

• A. 25 to 30%
• B. 40 to 50%
• C. 65 to 70%
• D. 85 to 90%

Explanation: With coal combustion plus heat-recovery equipment such as economisers, air preheaters and superheaters, modern boiler efficiency is…

• A. 30 metres
• B. 40 metres
• C. 60 metres
• D. 100 metres

Explanation: A screw conveyor is suitable for relatively short coal-handling runs because friction, power demand and alignment problems increase with…

• A. 30°
• B. 60°
• C. 80°
• D. 90°

Explanation: A conventional belt conveyor can transport coal on inclines up to approximately 30 degrees, although the practical angle depends on belt…

• A. condensing type
• B. non-condensing type
• C. none of the above

Explanation: Steam power stations commonly use condensing turbines because exhaust steam is condensed and returned as feedwater, while the vacuum at…

• A. four
• B. three
• C. two
• D. one

Explanation: Two safety valves provide protection against excessive boiler pressure, while allowing one valve to remain effective if the other requires…

• A. steel
• B. cast iron
• C. copper
• D. aluminium

Explanation: Steel withstands the high temperature and pressure of steam and has better mechanical strength than cast iron or aluminium.

• A. steam in pipes surrounded by water
• B. water in pipes surrounded by steam
• C. either A. or (b)
• D. none of the above

Explanation: In an evaporative condenser, steam flows inside tubes while water is sprayed over their outer surfaces and evaporates to remove heat.

• A. there is one pump to remove air and condensate
• B. there are two pumps to remove air and condensate
• C. there are three pumps to remove air, vapour and condensate
• D. there is no pump, the condensate gets removed by gravity

Explanation: A regenerative surface condenser uses separate pumps because air and condensate have different functions and are withdrawn separately.

• A. to maintain pressure below atmospheric to increase work output from the primemover
• B. to receive large volumes of steam exhausted from steam prime mover
• C. to condense large volumes of steam to water which may be used again in boiler
• D. all of the above

Explanation: A condenser receives turbine exhaust steam, maintains a vacuum to increase turbine work, and converts the steam back into reusable…

• A. removes air and also vapour from condenser
• B. removes only air from condenser
• C. removes only un-condensed vapour from condenser
• D. removes air alongwith vapour and also the condensed water from condenser

Explanation: An Edward's air pump is a wet air pump that removes air together with uncondensed vapour and condensate from the condenser.

• A. increases the quantity of vapour extracted along with air
• B. reduces the quantity of vapour extracted along with air
• C. does not affect vapour quantity extracted but reduces pump capacity of air extraction pump
• D. none of the above

Explanation: The cooling section condenses much of the vapour mixed with the extracted air before it reaches the air pump.

• A. fall in absolute pressure maintained in condenser
• B. rise in absolute pressure maintained in condenser
• C. no change in absolute pressure in the condenser
• D. rise in temperature of condensed steam

Explanation: Air entering a condenser raises its partial pressure and opposes condensation; removing it lowers the total absolute pressure and improves…

• A. steam and cooling water mix to give the condensate
• B. cooling water passes through the tubes and steam surrounds them
• C. steam passes through the cooling tubes and cooling water surrounds them
• D. all of the above varying with situation

Explanation: A shell-and-tube surface condenser keeps the fluids separate: cooling water flows inside the tubes and exhaust steam surrounds the tubes…

• A. cooling water passes through tubes and steam surrounds them
• B. steam passes through tubes and cooling water surrounds them
• C. steam and cooling water mix
• D. steam and cooling water do not mix

Explanation: Jet condensers are direct-contact condensers, so cooling water comes into direct contact and mixes with the exhaust steam.