# 3 Phase Synchronous MCQ Questions & Answers

3 Phase Synchronous MCQs : This section focuses on the "3 Phase Synchronous". These Multiple Choice Questions (MCQs) should be practiced to improve the 3 Phase Synchronous skills required for various interviews (campus interview, walk-in interview, company interview), placement, entrance exam and other competitive examinations.

Question 1

A 3-phase induction motor runs at almost 1500 rpm at no load and 900 rpm at full load when supplied with power from a 50 Hz, 3-phase supply. What is the corresponding speed of the rotor field with respect to the rotor?

A. 300 revolution per minute
B. 400 revolution per minute
C. 600 revolution per minute
D. 500 revolution per minute

Question 2

A 4-pole, 3-phase, 60 Hz induction motor is operating at a speed of 1500 rpm. The frequency of the rotor current of the motor in Hz is __________

A. 5
B. 4
C. 2
D. 7

Question 3

Calculate the active power in an 8 ? resistor with 8 A current flowing through it.

A. 512 W
B. 514 W
C. 512 W
D. 518 W

Question 4

Calculate the phase angle of the sinusoidal waveform z(t)=8cos(45t+2?÷15).

A. 2?÷39
B. 2?÷15
C. ?÷4
D. 2?÷44

Question 5

For a practical synchronous motor, the pull-out torque will occur when the torque angle is nearly equal to ________

A. 0°
B. 30°
C. 45°
D. 75°

Question 6

In a synchronous machine, the phase sequence can be reversed by reversing the _________

A. Rotor direction
B. Field polarities
C. Armature terminal
D. Rotor direction and armature terminal

Question 7

In an induction motor, when the number of stator slots is not equal to an integral number of rotor slots _________

A. There may be a discontinuity in torque slip characteristics
B. A high starting torque will be available
C. The machine performs better
D. The machine may fail to start

Question 8

The direct axis is taken along ________

A. Inter-polar axis
B. Rotor pole axis
C. In between inter polar and rotor axis
D. Parallel to interpolar axis

Question 9

The hunting phenomenon in a synchronous motor is also referred to as _________

A. Surging
B. Phase swinging
C. Cogging
D. Surging and phase swinging

Question 10

The slope of the V-I curve is 7°. Calculate the value of resistance. Assume the relationship between voltage and current is a straight line.

A. .122 ?
B. .360 ?
C. .377 ?
D. .578 ?

Question 11

Which of the following are used in preventing the hunting phenomenon in synchronous generators?

A. Damper bars
B. Short pitch chords
C. Distributed winding
D. Damper bars and short pitch chords

Question 12

Calculate the active power in an 8 Ω resistor with 8 A current flowing through it.

A. 512 W
B. 514 W
C. 512 W
D. 518 W

Question 13

Calculate the phase angle of the sinusoidal waveform z(t)=8cos(45t+2π÷15).

A. 2π÷39
B. 2π÷15
C. π÷4
D. 2π÷44