Explore topic-wise MCQs in Electrical Machines.

This section includes 15 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Machines knowledge and support exam preparation. Choose a topic below to get started.

1.

If the magnetic circuit of the dc machine is in the saturation region, the armature reaction __________

A. does not affect flux/pole
B. increases the flux/pole
C. decreases flux/pole
D. affects the flux/pole only when armature current is small
Answer» B. increases the flux/pole
2.

The compensating winding in dc generator is provided to __________

A. neutralize cross-magnetizing flux
B. neutralize demagnetizing flux
C. neutralize armature mmf
D. maintain magnetizing mmf
Answer» B. neutralize demagnetizing flux
3.

The armature reaction is produced mainly by __________

A. load current in armature
B. load current in field
C. all of the mentioned
D. none of the mentioned
Answer» B. load current in field
4.

The commutation process involves basically reversal of current in armature coil as it crosses MNA.

A. True
B. False
Answer» B. False
5.

Mark the most incorrect. In dc generator, commutation can be improved by __________

A. using interpoles
B. using carbon brushes
C. shifting brush axis in direction of armature rotation
D. none of the mentioned
Answer» B. using carbon brushes
6.

Each of the following is valid for interpoles except __________

A. they are connected in parallel with the armature so that they carry part of armature current
B. they are small yoke fixed poles spaced in between main poles
C. their polarity, in case of generator is same as that of main poles ahead
D. they automatically neutralize not only reactance voltage but cross-magnetization also
Answer» B. they are small yoke fixed poles spaced in between main poles
7.

A 400-V, 1000-A, lap wound dc machine has 10 poles, 860 armature conductors. The number of conductors in the pole face to give full compensation if pole face covers 70% of pole span is?

A. 3010
B. 4300
C. 2400
D. 2800
Answer» B. 4300
8.

The number of compensating conductors/pole faces is _______ (where Z is the number of active armature conductors/pole; A is number of parallel paths; Ia is the armature current).

A. Z/A*Ia
B. 2*A*Ia/Z
C. Z*Ia/A
D. Z/2A*Ia
Answer» B. 2*A*Ia/Z
9.

The absence of compensating winding lead to __________

A. statically induced emf in armature
B. fluctuations in supply
C. reduction in the flux
D. any of the mentioned
Answer» B. fluctuations in supply
10.

The principle contributors to magneto motive force is/are __________

A. field current and armature current
B. field excitation
C. electromagnetic torque
D. all of the mentioned
Answer» B. field excitation
11.

The coil under going commutation lies along _____ while the coil getting short circuited lies along ____ for a practical dc machine.

A. gna, mna
B. mna, gna
C. gna, gna
D. mna, mna
Answer» B. mna, gna
12.

If the critical commutation time is 2 ms but it was observed that the practical commutation took 2.5 ms. This is the case of __________

A. under commutation
B. over commutation
C. critical commutation
D. none of the mentioned
Answer» B. over commutation
13.

With no commutating poles used the brushes are given backward lead in the dc motor.

A. True
B. False
Answer» B. False
14.

The brushes should be shifted in _______ direction in generator for the satisfactory operation of commutation.

A. forward
B. reverse to rotation
C. all of the mentioned
D. none of the mentioned
Answer» B. reverse to rotation
15.

The brushes are placed __________

A. along geometrical neutral axis
B. perpendicular to geometrical neutral axis
C. along magnetic neutral axis
D. perpendicular to magnetic neutral axis
Answer» B. perpendicular to geometrical neutral axis