The synchronous speed of a 4-pole, 50 Hz induction motor is:

The correct answer is A: 1500 rpm. Synchronous speed Ns = 120f/P = (120 × 50)/4 = 1500 rpm.

In a 400 kV transmission line in India's western grid, if the series reactance is 0.35 Ω/km and the line length is 250 km, what is the total series reactance of the transmission line?

The correct answer is A: 87.5 Ω. Total series reactance = 0.35 Ω/km × 250 km = 87.5 Ω. This is a fundamental calculation for transmission line parameters commonly tested in GATE and ESE.

In a synchronous motor, the pull-out torque depends on:

The correct answer is C: Supply voltage and field excitation. Pull-out torque τmax = 1.5(PΦIf)/(ωs), depends on pole flux and field current (excitation) and supply voltage.

What is the primary purpose of shunt capacitors in power systems?

The correct answer is B: To improve voltage profile and reduce reactive power demand. Shunt capacitors supply reactive power locally, improving voltage profile and reducing the burden on generators and transmission lines to supply reactive power.

In a priority encoder, what determines which input is encoded when multiple inputs are active?

The correct answer is B: The input with highest priority (typically MSB or LSB). Priority encoders are designed with built-in priority logic where the highest priority input (usually MSB) is encoded when multiple inputs are active.

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Electrical Engg (EEE)
Electrical Machines

Electrical machines, power systems, circuits

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Difficulty: All Easy Medium Hard 21–23 of 23

Topics in Electrical Engg (EEE)

All Circuit Analysis 100 Electrical Machines 100 Power Systems 100 Control Systems 100 Power Electronics 100 Electrical Measurements 40 Digital Electronics 100

Q.21 Hard Electrical Machines

In a DC machine, armature reaction causes:

A Increase in output torque

B Distortion of main flux and reduction in net flux density

C Increase in efficiency

D Decrease in back EMF in generator mode

Correct Answer: B. Distortion of main flux and reduction in net flux density

EXPLANATION

Armature reaction is caused by armature MMF which distorts the main magnetic field, reduces net flux, and causes commutation issues. Compensation is needed through commutating poles.

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Q.22 Hard Electrical Machines

An 8-pole induction motor running at 720 rpm with 50 Hz supply has a slip of approximately:

A 0.04 or 4%

B 0.06 or 6%

C 0.08 or 8%

D 0.10 or 10%

Correct Answer: A. 0.04 or 4%

EXPLANATION

Ns = 120×50/8 = 750 rpm. Slip s = (750-720)/750 = 30/750 = 0.04 or 4%.

Test

Q.23 Hard Electrical Machines

The torque developed in a 3-phase induction motor is maximum at a slip of:

A 0 (synchronous speed)

B 1 (standstill)

C s = R2/X2 (rotor resistance/reactance ratio)

D 0.5

Correct Answer: C. s = R2/X2 (rotor resistance/reactance ratio)

EXPLANATION

Maximum torque occurs at slip sm = R2/X2. This is crucial for motor design and performance analysis.

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Electrical Engg (EEE) Electrical Machines

Electrical Engg (EEE)
Electrical Machines