Electrical Machine - II (3150910) MCQs

MCQs of Synchronous & Auto Synchronous Motors

Showing 21 to 30 out of 68 Questions
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21.

The main reason for embedding the damper winding in the pole face is to

(a)

Eliminate losses on account of air friction
(b)

Reduce bearing friction
(c)

Eliminate hunting and provide starting torque
(d)

Eliminate air friction
Answer:

Option (c)

22.

The maximum value of torque that a synchronous motor, can develop without losing its synchronism, is known as

(a)

Pull out Torque
(b)

Breaking Torque
(c)

Pull-in Torque
(d)

Slip Torque
Answer:

Option (a)

23.

What is the ratio of no-load speed to full load speed of a 500 kVA, 12 poles, 3300 V, 3 phase, 50 Hz synchronous motor?

(a)

Zero
(b)

One
(c)

Infinite 
(d)

1.1
Answer:

Option (b)

24.

In a synchronous motor, _________________________ for Under, normal and Over excitation respectively. 

(a)

Eb<V, Eb=V and Eb>V
(b)

Eb>V, Eb=V and Eb<V
(c)

Eb=V, Eb>V and Eb<V
(d)

Eb=V, Eb<V and Eb>V
Answer:

Option (a)

25.

The armature current of the synchronous motor has large values for

(a)

High excitation
(b)

Low excitation
(c)

Both high and low excitation
(d)

Normal excitation
Answer:

Option (c)

26.

The construction of a synchronous motor resembles which of the following machine

(a)

Differential compound motor
(b)

Alternator
(c)

DC series motor
(d)

Induction motor
Answer:

Option (b)

27.

Why synchronous motors are inherently not self-starting motor?

(a)

The direction of torque on the rotor reverses very fast (after every half cycle).
(b)

Slip is not present in synchronous machine
(c)

Starting winding is not present in the synchronous machine
(d)

Pulsating (not rotating) flux is produced in the stator 
Answer:

Option (a)

28.

If a synchronous motor fails to pull into synchronism after applying dc field current, the main cause is

(a)

Low short circuit ratio
(b)

High field current
(c)

High core losses
(d)

Low field current
Answer:

Option (d)

29.

Which of the following losses is not dissipated by the stator core surface in a synchronous motor?

(a)

Windage losses
(b)

Iron losses
(c)

Copper losses
(d)

Eddy current losses
Answer:

Option (a)

30.

The direction of rotation of the synchronous motor can be reversed by reversing

(a)

The polarity of the rotor poles
(b)

Field winding
(c)

Supply phase sequence
(d)

None of these
Answer:

Option (c)

Showing 21 to 30 out of 68 Questions
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