To avoid formation of grooves in the commutator of a D.C. machine
none of the above
brush position has no effect on the commutator grooving
the brushes of same polarity should track each other
the brushes of opposite polarity should track each other
the brushes of opposite polarity should track each other
A 220 V D.C. generator is run at full speed without any excitation. The open circuit voltage will be
zero
about 50 V
about 2 V
220 V
about 2 V
In a separately excited generator supplying rated load the armature reaction
is always present
none of the above
may be sometimes present
is always absent
is always present
Which of the following D.C. generators will be in a position to build up without any residual magnetism in the poles ?
None of the above
Shunt generator
Series generator
Compound generator
None of the above
In over compounded generator full load terminal voltage is
equal to no-load terminal voltage
more than no load terminal voltage
almost zero
less than no load terminal voltage
more than no load terminal voltage
The following constitute short-circuit in the armature winding.
All of the above
Insulation failure between two commutator bars
Insulation failure between two turns of a coil
Two of more turns of the same coil getting grounded
All of the above
In a D.C. generator in case the resistance of the field winding is increased then output voltage will
fluctuate heavily
remain unaffected
increase
decrease
decrease
In a level compounded D.C. generator full load terminal voltage is
negligibly low
more than no-load terminal voltage
equal to no-load terminal voltage
less than no-load terminal voltage
equal to no-load terminal voltage
The terminal voltage of a D.C. shunt generator drops on load because of all of the following reasons except
commutation
field weakening due to armature reaction and armature
armature resistance drop
armature reaction
commutation
If residual magnetism is present in a D.C. generator the induced e.m.f. at zero speed will be
zero
the same as rated voltage
small
high
zero
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