MCQs on Electrical Machines

Page 59 of 114. Go to page
01․ In a DC machine the armature mmf is
rotating with respect to field poles as well as armature.
rotating with respect to field poles.
stationary with respect to field poles.
stationary with respect to armature.

Under construction.
02․ Due to magnetic saturation, the flux per pole in a DC machine without brush shift
increases in generators but decreases in motor with load.
increases in both the generators and the motors with load.
decreases in generators and increases in motor with load.
decreases in both generators and the motors with load.

Under construction.
03․ A 250 V DC generator in run at rated speed with no excitation. The open circuit voltage will be
zero.
about 100 V.
very small, say about 2 or 3 V.
250 V.

Under construction.
04․ Short circuiting is caused in the armature winding due to
grounding of two or more turns of the same coil.
failure of insulation between two commutator bars.
failure of insulation between two turns of coil.
any of above.

Under construction.
05․ With the increases in field excitation of a DC generator, its generated emf
decreases.
increases.
remains constant.
increases upto a limit and then remains almost constant.

Under construction.
06․ The compensating winding in a DC machine
is located on commutating poles for improving commutation.
is located on pole shoes for avoiding the flashover at the commutator.
is located in armature slots for compensation of the armature reaction.
is located on pole shoes to avoid the sparking at the brushes.

Under construction.
07․ The slight curvature at the lower end of the OCC of a self excited DC generator is due to
high speed.
residual flux.
magnetic inertia.
high field resistance.

Under construction.
08․ A generator may loose residual magnetism due to
vibrations.
heating.
over excitation.
any of these.

Under construction.
09․ In DC generators, the residual magnetism is of the order of
2.5 %.
10 %.
15 %.
20 %.

Under construction.
10․ In large sized DC machines the compensating windings are provided to
reduce eddy current losses by providing local short circuits.
compensate for the decrease in speed due to increase of load.
neutralize voltage induced in coil due to fluctuation of l
none of the above.

Under construction.
<<<5758596061>>>