MCQs on Power Systems

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01․ In which power plant, the thermal efficiency is quite low
Diesel power plant.
Steam power plant.
Hydro power plant.
Nuclear power plant.

Because a steam power station, more than 50 % of total heat of combustion is lost as heat rejected to the condenser and the loss is unavoidable as heat energy can be convert into mechanical energy without a drop in temperature and the steam in condenser at the lower temperature.

02․ Which cooling is preferred for large turbine generator
Oxygen cooling.
Hydrogen cooling.
Nitrogen cooling.
None of these.

Hydrogen cooling is preferred because of following reasons - 1. It reduces windage losses to about one teeth of its value in air. 2. It provides better cooling. 3. It reduces the oxidation of the insulation and fire hazards. 4. It reduces the windage noise.

03․ A steam power generation has an overall efficiency of 20 %. 0.6 Kg of coal is burnt per kWh of electrical energy generated. Calculated the calorific value of fuel
7166.67 KCal / Kg.
7000 KCal / Kg.
7562 KCal / Kg.
7268.45 KCal / Kg.

Let x cal / Kg be the calorific value of fuel. Heat produce by 0.6 kg of coal= 0.6x Kcal. Heat equivalent of 1 KWh = 860 KCal. \

04․ What will be the thermal efficiency of a 240 V, 1000 W electric kettle if it brings 2 liters of water at 15° C to boiling point 15 Minutes
74.56 %.
78.96 %.
79.33 %.
80.25 %.


05․ Mechanical energy is supplied to a DC generator at the rate of 4200 J / S. The generator delivers 32.2 Amp at 120 V. How much energy is cost per minute of operation
20060 J.
20160 J.
23060 J.
25060 J.


06․ A diesel power station has fuel consumption of 0.28 Kg per kWh. The calorific value of fuel is being 10000 KCal / kg. Determine the overall efficiency
30.26 %.
30.7 %.
40 %.
40.85 %.

Heat produce by 0.28 Kg of oil = 10000 × 0.28 = 2800 KCal. Heat produced equivalent of 1 KWh = 860 KCal. \

07․ Example of base load stations are
both A and B.
gas turbine.

Base load stations installed of the capacity of unvarying load known as base load which is normally required for the whole day.

08․ The time taken by the turbine to fall to 0 rpm speed from 3000 rpm is called
settling time.
coasting time.
stopping time.
damping time.

The time taken by the turbine to fall to 0 rpm speed from 3000 rpm is called coasting time (technically called) and it is generally 40 min.

09․ Load frequency control is achieved by properly matching the individual machines
turbine inputs.
reactive powers.
generator ratings.
generated voltages.

The load frequency control of 2 machines can be achieved by matching both turbine inputs.

10․ Uses of diesel power stations
peak load plant.
emergency plants.
standby plants.
all of the above.

Diesel power station is an example of peak load station which is installed to share the peak load of the base load station during peak load hours.