All Free Electrical Engineering MCQs with Answers

• A. less
• B. more
• C. same
• D. not predictable

Explanation: An induced-draught fan handles hot flue gases, whose volume is larger than that of the relatively cool air handled by a forced-draught fan…

• A. forced fan
• B. chimney
• C. steam jet
• D. only motion of locomotive

Explanation: Locomotive boilers commonly use the exhaust steam jet in the smokebox to draw flue gases through the firebox and boiler tubes.

• A. to produce draught to accelerate the combustion of fuel
• B. to discharge gases high up in the atmosphere to avoid hazard
• C. to reduce the temperature of the hot gases discharged
• D. none of the above

Explanation: With forced draught, the fan supplies the combustion air, so the chimney is not primarily needed to create draught.

• A. less
• B. more
• C. same
• D. may be more or less

Explanation: For equal height, a steel chimney generally produces more draught because it heats up quickly and maintains hotter gases, while its smooth…

• A. decreases if the chimney gas temperature increases
• B. increases if the chimney gas temperature increases
• C. remains same irrespective of chimney gas temperature
• D. may increase or decrease

Explanation: Chimney draught increases when the chimney gases become hotter because their density falls, increasing the pressure difference between the…

• A. decreases with increase in outside air temperature
• B. increases with increase in outside air temperature
• C. remains the same irrespective of outside air temperature
• D. may increase or decrease with increase in outside air temperature

Explanation: Draught depends on the density difference between outside air and chimney gases.

• A. induced draught
• B. natural draught
• C. forced draught
• D. balanced draught

Explanation: A chimney creates draught naturally through the density difference between hot flue gases and cooler outside air, without a fan.

• A. impulse turbines
• B. reaction turbines
• C. impulse-reaction turbines
• D. none of the above

Explanation: Most modern steam turbines use impulse-reaction stages, combining pressure drop in fixed and moving blades.

• A. air
• B. feed water
• C. flue gases
• D. all above

Explanation: An economiser recovers heat from flue gases to preheat the boiler feed water before it enters the boiler.

• A. equal to diesel power station
• B. more than diesel power station
• C. less than diesel power station

Explanation: A steam station needs boilers, turbines, condensers, cooling equipment, coal-handling systems and often ash-handling plant.

• A. increase the performance of the condenser
• B. increase the efficiency of the plant
• C. increase efficiency of the turbine

Explanation: A binary vapour cycle uses two working fluids so that heat addition and rejection can better match the available temperature ranges.

• A. higher critical temperature and pressure
• B. higher saturation temperature than other fluids
• C. relatively low vapourisation pressure
• D. all above

Explanation: Mercury has a high critical temperature, high saturation temperature and relatively low vapour pressure, making it suitable as the topping…

• A. utilise heat of flue gases
• B. increase thermal efficiency
• C. improve condenser performance
• D. reduce loss of heat

Explanation: Reheating expands steam in stages and returns it to the boiler for reheating between stages, raising the average temperature of heat…

• A. exhaust gases
• B. heaters
• C. draining steam from the turbine
• D. all above

Explanation: Regenerative heating uses steam bled or drained from intermediate turbine stages to heat the feedwater in feed heaters.

• A. increases with number of feed heaters increasing
• B. decreases with number of feed heaters increasing
• C. remains same unaffected by number of feed heaters
• D. none of the above

Explanation: Adding feed heaters raises the average temperature at which heat is supplied, so the maximum efficiency gain increases as more heaters are…

• A. when steam is extracted from only one suitable point of steam turbine
• B. when steam is extracted from several places in different stages of steam turbine
• C. when steam is extracted only from the last stage of steam turbine
• D. when steam is extracted only from the first stage of steam turbine

Explanation: Several extraction points heat the feedwater in stages, matching the water temperature more closely to the turbine expansion temperatures.

• A. decreases with increase in Rankine cycle efficiency
• B. increases with increase in Rankine cycle efficiency
• C. is unaffected by increase in Rankine cycle efficiency
• D. none of the above

Explanation: As the basic Rankine cycle becomes more efficient, the optimum regenerative arrangement generally uses a larger fraction of extracted…

• A. is always greater than simple Rankine thermal efficiency
• B. is greater than simple Rankine cycle thermal efficiency only when steam is bled at particular pressure
• C. is same as simple Rankine cycle thermal efficiency
• D. is always less than simple Rankine cycle thermal efficiency

Explanation: Regeneration increases the mean temperature of heat addition and therefore raises thermal efficiency compared with the corresponding…

• A. change of internal energy between inlet and outlet
• B. change of enthaply between inlet and outlet
• C. change of entropy between inlet and outlet
• D. change of temperature between inlet and outlet

Explanation: For steady, adiabatic turbine flow with negligible changes in kinetic and potential energy, turbine specific work equals the enthalpy…

• A. improves in summer as compared to that in winter
• B. improves in winter as compared to that in summer
• C. is unaffected by climatic conditions
• D. none of the above

Explanation: Cooler winter conditions lower the condenser cooling-water temperature and improve the condenser vacuum.