The settling time of a second-order underdamped system is approximately given by:

The correct answer is A: ts ≈ 4/(ζωₙ). For 2% criteria, settling time ts ≈ 4/(ζωₙ). This is the standard formula for second-order systems.

In a 3-phase synchronous generator, the pitch factor (or coil span factor) accounts for:

The correct answer is B: Span of the coil not covering all poles. Pitch factor (Kp) accounts for the reduction in EMF when the coil span is less than the pole pitch (full pitch), representing incomplete flux linkage.

In a three-level diode-clamped inverter (Neutral Point Clamped), the advantage over two-level inverter is:

The correct answer is B: Lower dv/dt and reduced EMI. Three-level inverter generates three voltage levels, reducing the step size and dv/dt compared to two-level inverter, thus reducing EMI and stress on motor windings.

What is the effect of increasing system frequency above nominal value in a power system?

The correct answer is C: Increases inductive reactance (X = 2πfL) and reduces capacitive reactance. Since inductive reactance X_L = 2πfL and capacitive reactance X_C = 1/(2πfC), increasing frequency increases X_L and decreases X_C.

For a system with open-loop transfer function G(s)H(s) = K/[s(s+1)(s+2)], the number of asymptotes in root locus is:

The correct answer is B: 2. Number of asymptotes = n - m = 3 - 1 = 2, where n=3 (poles) and m=1 (zeros).

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Electrical Engg (EEE)
Electrical Machines

Electrical machines, power systems, circuits

27 Q 7 Topics Take Mock Test

Difficulty: All Easy Medium Hard 21–27 of 27

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 Easy Electrical Machines

A 3-phase induction motor has 4 poles and is connected to a 50 Hz supply. What is the synchronous speed?

A 1500 rpm

B 1000 rpm

C 3000 rpm

D 750 rpm

Correct Answer: A. 1500 rpm

EXPLANATION

Synchronous speed Ns = 120f/P = 120×50/4 = 1500 rpm

Test

Q.22 Easy Electrical Machines

In a transformer, the turns ratio k = N2/N1. If k > 1, the transformer is:

A Step-down transformer

B Step-up transformer

C Isolation transformer

D Auto transformer

Correct Answer: B. Step-up transformer

EXPLANATION

When secondary turns are greater than primary turns (k > 1), voltage is stepped up.

Test

Q.23 Easy Electrical Machines

The slip of an induction motor is defined as:

A (Ns - Nr)/Ns

B (Nr - Ns)/Nr

C Ns/Nr

D (Ns - Nr)/Nr

Correct Answer: A. (Ns - Nr)/Ns

EXPLANATION

Slip s = (Ns - Nr)/Ns, where Ns is synchronous speed and Nr is rotor speed.

Test

Q.24 Easy Electrical Machines

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

A 1500 rpm

B 3000 rpm

C 750 rpm

D 1000 rpm

Correct Answer: A. 1500 rpm

EXPLANATION

Synchronous speed Ns = 120f/P = (120 × 50)/4 = 1500 rpm.

Test

Q.25 Easy Electrical Machines

In a three-phase induction motor, the rotating magnetic field is produced by:

A Rotor current alone

B Three-phase stator currents with 120° phase difference

C DC excitation in stator

D Permanent magnets in rotor

Correct Answer: B. Three-phase stator currents with 120° phase difference

EXPLANATION

Three-phase currents 120° apart create a rotating magnetic field that rotates at synchronous speed Ns = 120f/P.

Test

Q.26 Easy Electrical Machines

The back EMF in a DC motor is given by the expression?

A E = PφZN/60

B E = PφZN/120

C E = φZN/60

D E = 2PφZN/60

Correct Answer: B. E = PφZN/120

EXPLANATION

Back EMF in DC motor: Eb = PφZN/120 where P = poles, φ = flux, Z = conductors, N = speed in rpm.

Test

Q.27 Easy Electrical Machines

Which of the following is the primary function of a commutator in a DC machine?

A To convert AC to DC

B To reverse the direction of current in armature conductors

C To reduce iron losses

D To increase flux density

Correct Answer: B. To reverse the direction of current in armature conductors

EXPLANATION

The commutator reverses the direction of current in armature conductors as they move from one pole to another, ensuring unidirectional torque production.

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