EE MCQ

SSC JE Electrical 2019 with solution SET-1
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The average value of a sinusoidal wave is:

The average value of the sine wave over one complete cycle is actually zero. Hence, for a sine wave, the average value is defined over half the period. The average value expressed in terms of peak value is given by

Average value = 0.637 × peak value

Related Question

SSC JE Electrical 2019 with solution SET-1
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An alternator has 9 slots/pole. What is the value of the pitch factor if each coil spans 8 slot pitches

Coil Span = 8

Pole Pitch = 9 slots/pole

Slot angle (α) = 180° / Pole Pitch = 180°/9 = 20°

Pitch Factor = cos(α/2) = cos (20/2)

Pitch Factor = cos 10°

SSC JE Electrical 2019 with solution SET-1
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The law that explains about the economic size of a conductor is:

In transmission lines, a large amount of power is transmitted over a long distance. So, voltage regulation is not important because in some lines, 40% regulation is considered satisfactory. In such cases, only the economy is important. The cost of the conductor is the main part which decides the total cost of the transmission line. Hence, the selection of the proper size of the conductor for a particular line is most important.

The most economical area of the conductor is that for which the total annual cost of the transmission line is minimum. This is known as Kelvin’s law and was given by Lord Kelvin in the year 1881.

It states that the most economical cross-section of a conductor is the value at which the annual cost of the electric energy wasted in the conductor, and annual cost of the interest and depreciation on the capital cost of the conductor are equal. Thus, the total annual charge on an overhead transmission line can be expressed as :

Total annual charge =P1 + P2α or Variable part of the energy charge = Annual cost of energy wasted.

where

P1 and P2 are constants

α is the area of the X-section of the conductor.

SSC JE Electrical 2019 with solution SET-1
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The Norton’s current in the circuit shown below is

According to the Norton theorem, to find the Norton current, first remove the load resistance RL from the network terminals AB. Short circuit the terminals AB as shown in Figure calculate the current ISc or IN through the short circuit.

Now resistance of 150Ω will not show any effect in the circuit. So only resistance of 30Ω will be effective.

Norton current IN = 360/30

IN = 12 A

SSC JE Electrical 2019 with solution SET-1
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Find the mutual inductance between two ideally coupled coils of 2H and 8H

Mutual inductance between the two coils is K = √L1.L2

K = √2 × 8

k = √16

k = 4 H