1141.
In a D.C. generator all of the following could be the effects of iron losses except
A
Loss of efficiency
B
Excessive heating of core
C
Increase in terminal voltage
D
Rise in temperature of ventilating air
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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
For which types of D.C. motor, dynamic braking is generally used ?
Compound motors
All of the above
Shunt motors
Series motors
For which of the following applications a D.C. motor is preferred over an A.C. motor ?
Variable speed operation
Fixed speed operation
Low speed operation
High speed operation
For the same H.P. rating and full load speed, following motor has poor starting torque
differentially compounded
cumulativelycompounded
shunt
series
For starting a D.C. motor a starter is required because
it starts the motor
none of the above
it limits the speed of the motor
it limits the starting current to a safe value
For constant torque drive which speed control method is preferred ?
Shunt armature control
Mechanical loading system
Field control
Armature voltage control
For a D.C. shunt motor if the excitation is changed
torque and power both will change
torque, power and speed, all will change
torque will remain constant
torque will change but power will remain constant
Following motor is used where high starting torque and wide speed range control is required.
Single phase capacitor start
Induction motor
Synchronous motor
D.C. motor
Flywheel is used with D.C. compound motor to reduce the peak demand by the motor, compound motor will have to be
level compounded
under compounded
cumulatively compounded
differentially compounded