Electrical Machine - II (3150910) MCQs

MCQs of Synchronous & Auto Synchronous Motors

Showing 51 to 60 out of 68 Questions
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51.

When the excitation voltage is increased from 1 to 1.3 pu of a 3-phase synchronous motor. Then load angle for the constant power operation ________

(a)

must be increased
(b)

must be decreased
(c)

remain constant
(d)

Cant comment, need speed variation data
Answer:

Option (b)

52.

For a power system having induction motor loads, an overexcited synchronous motor is also attached. The induction motor will now operate at ________

(a)

lagging
(b)

leading
(c)

reduced power factor
(d)

increased power factor
Answer:

Option (a)

53.

For a synchronous motor, Curev A & Curve B representing ___________ & _________ respectively.

(a)

Lagging & Leading PF
(b)

Leading & Lagging PF
(c)

Lagging & Unity PF
(d)

Lagging & Lagging PF 
Answer:

Option (a)

54.

The voltage equation of the synchronous motor is?

(a)

V=Eb+IaRa+jXs
(b)

V=Eb-IaRa+jXs
(c)

V=Eb+IaRa-jXs
(d)

V=Eb-IaRa-jXs
Answer:

Option (a)

55.

A 415 V synchronous motor is working at 30° load angle. What can be the expected phasor?

(a)

A
(b)

B
(c)

C
(d)

D
Answer:

Option (a)

56.

The synchronous motor is operating at UPF. The most suitable phasor will be?

(a)

A
(b)

B
(c)

C
(d)

D
Answer:

Option (a)

57.

When load on a synchronous motor is increased, its armature currents in increased provided it is

(a)

Normally-excited
(b)

Over-excited
(c)

Under-excited
(d)

All of the above
Answer:

Option (d)

58.

When load on a synchronous motor running with normal excitation is increased, armature current drawn by it increases because

(a)

Back e.m.f. Eb becomes less than applied voltage V
(b)

Power factor is decreased
(c)

Net resultant voltage ER in the armature is increased
(d)

Motor speed is reduced
Answer:

Option (c)

59.

The  speed of a synchronous motor can be changed by changing ___________ .

(a)

Supply Voltage
(b)

Supply Frequency
(c)

Excitation 
(d)

All of these 
Answer:

Option (b)

60.

An important advantages of a synchronous motor over wound round induction motor is that

(a)

Its speed may be controlled more easily
(b)

Its speed is independent of supply frequency
(c)

Its power factor may be varied at will
(d)

None of the above
Answer:

Option (c)

Showing 51 to 60 out of 68 Questions
3 4 5 6 7