MCQs on Electrical Machines

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01․ If the armature electric current is increased to double its previous value, and the time of commutation is halved, how will the reactance voltage vary?
It will be halved.
It will remain the same.
It will be doubled.
It will becomes four times.

Under construction.
02․ To have sparkless commutation, the armature reaction effect in a DC machine is neutralized by
increasing field excitation.
compensating winding and commutating poles.
shifting the brush axis from GNA to MNA.
fixing the brush axis inline with the pole axis.

Under construction.
03․ Armature reaction of an unsaturated DC machine is
crossmagnetising.
demagnetising.
magnetising.
none of above.

Under construction.
04․ Iron losses in a DC machine are independent of variation in
load.
speed.
voltage.
speed and voltage.

Under construction.
05․ In a DC generator in case the brushes are moved so as to bring them in magnetic neutral axis, then, there will be
cross-magnetisation.
demagnetisation.
cross-magnetization as well as demagnetization.
none of above.

Under construction.
06․ In a DC generator, the armature reaction results in
magnetization of inter poles.
demagnetization of centers of poles.
magnetization of leading and demagnetization of trailing pole tip.
demagnetization of leading & magnetization of trailing pole tip.

Under construction.
07․ In a DC generator the actual flux distribution depends upon
shape of the pole shoe.
size of air gap.
clearance between tips of the adjacent pole shoes.
all of above.

Under construction.
08․ The demagnetising component of armature reaction in a DC generator
reduces inter poles flux density.
reduces generator emf.
results in sparking trouble.
increases armature speed.

Under construction.
09․ Armature coil is short circuited by brushes when it lies
along field axis.
along neutral axis.
in any of above positions.
in none of above positions.

Under construction.
10․ Compensating windings are used in DC generators
to provide path for the circulation of cooling air.
to neutralize the cross magnetizing effect of the armature reaction.
mainly to reduce the eddy currents by providing local short circuit.
none of the above.

Under construction.
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