MCQs on Power Systems

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01․ Calorific value of solid fuel is expressed as
KCal / gm.
Cal / gm.
KCal / lt.
Cal / lt.

Calorific value is amount of heat produced by complete combustion of a unit of weight of fuel. It is expressed as Cal / gm or KCal / kg.

02․ Percentage of carbon is highest in
anthracite coal.
bituminous coal.
lignite coal.
coal gas.

Percentage of carbon C is highest in anthracite coal about of 90 %.

03․ Cheapest plant in operation and maintenance is
steam power.
diesel power.

Hydroelectricity eliminates the flue gas emissions from fossil fuel combustion, including pollutants such as sulfur dioxide, nitric oxide, carbon monoxide, dust, and mercury in the coal. Hydroelectricity also avoids the hazards of coal mining and the indirect health effects of coal emissions. Compared to nuclear power, hydroelectricity generates no nuclear waste, has none of the dangers associated with uranium mining, nor nuclear leaks. Unlike uranium, hydroelectricity is also a renewable energy source. Compared to wind farms, hydroelectricity power plants have a more predictable load factor. If the project has a storage reservoir, it can generate power when needed. Hydroelectric plants can be easily regulated to follow variations in power demand.

04․ The positive sequence reactance will be equal to negative sequence if the equipment is
transformer and transmission lines.
none of these.

Transformer and transmission lines have no rotational part so positive and negative sequence reactance will be equal.

05․ The sequence components of the fault current are as follows : Ipositive = j1.5 pu, Inegative = − j0.5 pu, Izero = − j pu Which fault is this?

Only LLG fault current has a unique property that the sum of all sequence components of the fault current is zero.

06․ On a power system network the load is increasing represents the value of impedance
remains constant.
none of above.

Normally 70 % of loads are inductive in nature. If at all load is increasing then inductor in parallel is increasing. Hence inductive reactance will decrease. As we know that, Z = R + j ( XL - XC ). Hence impedance will decease.

07․ If a fault occurs on any feeder, the fault current is
much higher than with unsectional bus bar.
much lower than with unsectional bus bar.
equal to unsectional bus bar.
none of these.

The fault current is much lower than with unsectionalized bus bar because a feeder fault is fed from one section.

08․ A loss less transmission line having surge impedance loading (SIL) of 2280 MW is provided with a uniformly distributed series capacitive compensation of 30 %. Then SIL of compensated transmission line will be
2280 MW.
1835 MW.
3257 MW.
2725 MW.

There will not be any effect on active power capacitive compensation. ⇒ SIL = 2280 MW.

09․ When a neutral point of 3 - Φ system is directly connected to earth then it has what type of grounding?
Peterson coil.

A neutral point of a 3 phase system is directly connected to earth through a wire of negligible resistance and reactance. It is said to be solid or effective grounding.

10․ In a three-phase system, when the loads are perfectly balanced, the neutral current is
one - third of maximum.
one - third of minimum.
two - thirds of maximum.

Under perfectly balanced condition current through the 3 different phases are equal and no current flows through the neutral.