1121.
One D.C. motor drives another D.C. motor. The second D.C. motor when excited and driven
A
runs as a generator
B
does not run as a generator
C
also runs as a motor comes to stop after sometime
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One D.C. motor drives another D.C. motor. The second D.C. motor when excited and driven
runs as a generator
does not run as a generator
also runs as a motor comes to stop after sometime
No-load speed of which of the following motor will be highest ?
Shunt motor
Series motor
Cumulative compound motor
Differentiate compound motor
In which of the following applications D.C. series motor is invariably tried?
Starter for a car
Drive for a water pump
Fan motor
Motor operation in A.C. or D.C.
In Ward-Leonard control the lower limit of speed is imposed by
residual magnetism of the generator
core losses of motor
mechanical losses of motor and gen¬erator together
all of the above
In variable speed motor
a stronger commutating field is needed at low speed than at high speed
a weaker commutating field is needed at low speed than at high speed
same commutating field is needed at low speed than at high speed
none of the above is correct
In the D.C. motor the iron losses occur in
the field
the armature
the brushes
the commutator
In D.C. shunt motors as load is reduced
the speed will increase abruptly
the speed will increase in proportion to reduction in load
the speed will remain almost/constant
the speed will reduce
In D.C. motor which of the following can sustain the maximum temperature rise?
Slip rings
Commutator
Field winding
Armature winding
In D.C. machines the residual magnetism is of the order of
2 to 3 per cent
10 to 15 per cent
20 to 25 per cent
50 to 75 per cent
In D.C. machines fractional pitch winding is used
to improve cooling
to reduce copper losses
to increase the generated e.m.f.
to reduce the sparking
In case-the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be
100%
around 90%
anywhere between 75% and 90%
less than 50%
In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will
remain unchanged
reduce to one-fourth value
increase four folds
be doubled
In case of D.C. shunt motors the speed is dependent on back e.m.f. only because
back e.m.f. is equal to armature drop
armature drop is negligible
flux is proportional to armature current
flux is practically constant in D:C. shunt motors
In case of conductively compensated D.C. series motors, the compensating winding is provided
as separately wound unit
in parallel with armature winding
in series with armature winding
in parallel with field winding
In a manual shunt motor starter
over load relay is connected in series and no volt relay in parallel with the load
over load relay is connected in paral¬lel and no volt relay in series with the load
over load relay and no volt relay are both connected in series with the load
over load relay and no volt relay are both connected in parallel with the load
In a differentially compounded D.C. motor, if shunt field suddenly opens
the motor will first stop and then run in opposite direction as series motor
the motor will work as series motor and run at slow speed in the same direction
the motor will work as series motor and run at high speed in the same direction
the motor will not work and come to stop
In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be
almost negligible
rated full-load current
less than full-load current
more than full-load current
In a D.C. shunt motor, speed is
independent of armature current
directly proportional to the armature current
proportional to the square of the current
inversely proportional to the armature current
In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal to
100% of the previous value
50% of the previous value
25% of the previous value
10% of the previous value
In a D.C. generator, the iron losses mainly take place in
yoke
commutator
armature conductors
armature rotor