As a result of armature reaction the reduction in the total mutual air gap flux in a D.C. generator is approximately
10 percent
5 percent
40 percent
25 percent
5 percent
The demagnetising component of armature reaction in a D.C. generator
reduces generator e.m.f.
increases armature speed
reduces interpoles flux density
results in sparking trouble
reduces generator e.m.f.
Magnetic field in a D.C. generator is produced by
none of the above
both and
permanent magnets
electromagnets
electromagnets
The number of brushes in a commutator depends on
speed of armature
type of winding
amount of current to be collected
voltage
amount of current to be collected
Compensating windings are used in D.C. generators
to neutralise the cross-magnetising effect of the armature reaction
none of the above
to provide path for the circulation of cooling air
mainly to reduce the eddy currents by providing local short-circuits
to neutralise the cross-magnetising effect of the armature reaction
In a D.C. generator the actual flux distribution depends upon
all of the above
shape of the pole shoe
size of air gap
clearance between tips of the adjacent pole shoes
all of the above
Shunt generators are most suited for stable parallel operation because of their
linear voltage characteristics
drooping voltage characteristics
rising voltage characteristics
identical voltage characteristics
drooping voltage characteristics
In a shunt generator the voltage build up is generally restricted by
saturation of iron
speed limitation
armature heating
insulation restrictions
saturation of iron
If a D.C. generator fails to build up the probable cause could not be
faulty shunt connections tending to reduce the residual magnetism
no residual magnetism in the generator
imperfect brush contact
field resistance less than the critical resistance
field resistance less than the critical resistance
Eddy currents are induced in the pole shoes of a D.C. machine due to
oscillating magnetic field
pulsating magnetic flux
relative rotation between field and armature
all above
relative rotation between field and armature
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