SSC JE 2014 Electrical question paper with solution(Morning-Shift)

By applying current division Rule

Air blast circuit breaker is small in size, because of the growth of dielectric strength is so rapid (which final contact gap needed for arc extinction is very small) so isolator is used to switch off the voltage.

Diversity factor = Sum of individual maximum demand/ Station maximum demand.

Diversity helps to improve the load factor and economic operation of the power plant.

Load factor = Average load/ Maximum Demand

Both load factor and diversity factors are inversely proportional to maximum demand. Higher load factor and diversity factor means steady consumption or supply which means less maximum demand thus the initial and running cost will be low. Therefore the cost per unit of power generation will be less.

The fixed or standing charge to cover the first cost is divided into all the units used during that period. The more units used (and the higher the load factor), the less will be the fixed cost per unit.

The voltage regulation of an alternator is defined as the change in its terminal voltage when the full load is removed, keeping field excitation and speed constant, to the rated terminal voltage.

Where Vph = Rated terminal voltage

Eph =No load-induced e.m.f

An increase in the load current in a pure resistive load causes a decrease in the output voltage. For an inductive load an increase in the load current causes a greater voltage drop as compared to the resistive load. Therefore for inductive and resistive load conditions there is always drop in the terminal voltage hence regulation values are always positive.

In the case of leading load which means capacitive load, the effect of armature flux on main field flux is magnetizing i.e, the armature flux is adding up with the main field flux. Since it is adding up, the total induced emf(Vph) will also be more than the induced emf at no load(Eph).Hence the regulation is negative

The highest transmission A.C voltage in India is 750 KV till now.

According to the latest report Power Grid Corporation of India (PGCIL) has operationalized its ultra-high voltage 1200 kV National Test Station (NTS) at Bina in Madhya Pradesh and it is the highest operational transmission voltage level (including ac and dc operational voltage level) in the world.

At the centre of a current-carrying coil, the magnetic field intensity is directly proportional to the current and inversely proportional to the radius of the coil.

The slots are not made parallel to each other but are bit skewed as the skewing prevents magnetic locking of stator and rotor teeth and makes the working of the motor more smooth and quieter.

The current flowing through the capacitor is given by

I(t) =Cdv(t)/dt

Where I(t) is instantaneous current

C = capacitance in farad

dv/dt =instanaeous rate of voltage changed

In series resonance circuit  Z = R = V/I_m

Half power frequency is the frequency when the magnitude of voltage or current is decreased by the factor of 1/√2 from its maximum value. (Also known as cut-off frequency)

Therefore at half power frequency

I = I_m/√2

Now impedance at half power frequency

= V/I_m/√2 = √2V/I_m =√2R

Then referring the RL =10Ω on the primary side for matching the source impedance 

Transformer ratio is given by general expression

(N2/N1)² = (V2/V1)

As we know, V = IR

(N2/N1)² = (I2.R2/I1.R1)

I1 = I2…..(as currents are equal)

(N₂/N₁)²=(R₂/R1)

R₂ =R₁(N₂/N₁)²

10 = 6250(N2/N1)²

(N2/N1)² = 625

(N2/N1) = 25