MCQs on Electrical Machines

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01․ In DC generator on no-load, the air gap flux distribution in space is
pulsating.
triangular.
sinusoidal.
flat topped.

Under construction.
02․ Flashing the field of DC generator means
making the magnetic losses forces parallel.
increasing flux density by adding extra turns of winding.
neutralising residual magnetism.
creating residual magnetism by a DC source.

Under construction.
03․ Open circuited armature coil of a DC machine is
indicated by a spark completely around the commutator.
identified by scarring of commutator segment.
both of the above.
none of the above.

Under construction.
04․ In a Dc generator the magnetic neutral axis coincide with geometrical neutral axis, when
the generator runs on designed speed.
there is no load on the generator.
the generator runs on overload.
the generator runs on full load.

Under construction.
05․ A 220 V DC generator is run at full speed without any excitation. The open circuit voltage will be
zero.
about 2 V.
about 50 V.
220 V.

Under construction.
06․ If residual magnetism is present in a DC generator, the induced emf at zero speed will be
small.
high.
zero.
the same as rated voltage.

Under construction.
07․ The armature mmf of a DC machine has
triangular space distribution and rotates at the speed of armature.
stepped distribution and rotates at the speed of armature.
trapezoidal space distribution and is stationary in space.
triangular space distribution and is stationary in space.

Under construction.
08․ The armature MMF waveform of a DC machine is
pulsating.
triangular.
rectangular.
sinusoidal.

Under construction.
09․ In a DC generator, the ripples in the direct emf generated are reduced by employing
carbon brushes.
graphite brushes.
commutator with large number of segments.
equalizer rings.

Under construction.
10․ To avoid formation of grooves in the commutator
the brushes of opposite polarity should track each other.
the brushes of same polarity should track each other.
brush position has no effect on the commutator grooving.
none of the above.

Under construction.
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