Electrical Engineering Mcqs Practice Test

Question 1

In a synchronous motor, the magnitude of stator back e.m.f. Eb depends on___________?

Accepted Answer

B. d.c. excitation only

Question 2

Hunting in a synchronous motor cannot be due to___________?

Accepted Answer

A. windage friction

Question 3

A synchronous motor connected to infinite bus-bars has at constant full load, 100% excitation and unity power factor. On changing the excitation only, the armature current will have_____________?

Accepted Answer

D. leading power factor with over-excitation

Question 4

A synchronous motor develops maximum power when load angle is____________?

Accepted Answer

C. 90°

Question 5

The armature current of the synchronous motor

Accepted Answer

C. has large values for low and high excitation

Question 6

Exciters of synchronous machines are______________?

Accepted Answer

B. d.c. shunt machines

Question 7

The duration of sudden snort-circuit test on a synchronous motor is usually about_____________?

Accepted Answer

C. one second

Question 8

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

Accepted Answer

D. synchronising torque

Question 9

Which of the following motors is non-self starting ?

Accepted Answer

B. synchronous motor

Question 10

The magnitude of field flux in a 3-phase synchronous motor?

Accepted Answer

D. remains constant at all loads

Question 11

The ratio of starting torque to running torque in a synchronous motor is____________?

Accepted Answer

A. zero

Question 12

The induced e.m.f. in a synchronous motor working on leading power factor will be_____________?

Accepted Answer

A. more than the supply voltage

Question 13

Which of the following resistances can be measured by conducting insulation resistance test on a synchronous motor ?

Accepted Answer

D. All of the above

Question 14

The speed of a synchronous motor:

Accepted Answer

C. always remains constant

Question 15

When a 3-phase synchronous generator is supplying a zero power factor lagging load, the armature field affects the main field in the following way

Accepted Answer

B. directly opposes it

Question 16

If in a synchronous motor, driving mechanical load and drawing current at lagging power factor from constant voltage supply, its field excitation is increased, then its power factor__________?

Accepted Answer

B. become less

Question 17

Change of D.C. excitation of a synchronous motor changes:

Accepted Answer

B. power factor of power drawn by the motor

Question 18

The mechanical displacement of the rotor with respect to the stator, in polyphase multipolar synchronous motors running at full load, is of the order of_____________?

Accepted Answer

C. five degrees

Question 19

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

Accepted Answer

A. its power factor may be varied at will

Question 20

The angle between the rotating stator flux and rotor poles is called _________ angle.

Accepted Answer

C. torque