121 practice sets · Page 2 of 7
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
In a D.C. generator all of the following could be the effects of iron losses except
Loss of efficiency
Excessive heating of core
Increase in terminal voltage
Rise in temperature of ventilating air
If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking
regenerative
plugging
dynamic braking
none of the above
If the supply voltage for a D.C. motor is increased, which of the following will decrease ?
Starting torque
Operating speed
Full-load current
All of the above
If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will
remain same
become zero
increase
decrease
If the field of a D.C. shunt motor gets opened while motor is running
the motor will attain dangerously high speed 1
the motor will continue to nuvat constant speed
the speed of motor will be reduced %
the armature current will reduce
If I2 be the armature current, then speed of a D.C. shunt motor is
varies as (Ia)
varies as la
independent of Ia
proportional to la
If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens
this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
motor will run at very slow speed
nothing will happen to th£ motor
this will make armature to take heavy current, possibly burning it
If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens
nothing will happen to motor
motor will come to stop
this will make armature to take heavy current, possibly burning it
this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
If a D.C. motor is to be selected for conveyors, which rriotor would be preferred ?
Differentially compound motor
Cumulative compound motor
Series motor
Shunt motor
If a D.C. motor is connected across the A.C. supply it will
run at lower speed
burn due to heat produced in the field winding by .eddy currents
run at normal speed
not run
If a D.C. motor designed for 40°C ambient temperature is to be used for 50°C ambient temperature, then the motor
can be used for 50°C ambient temperature also
is to be derated by a factor recom-mended by manufacturer and select the next higher H.P. motor
of lower H.P. should be selected
of higher H.P. should be selected
Hopkinsons test on D.C. machines is conducted at
full-load
overload
no-load
part load
