1. Which of the following steps is likely to result in reduction of hysteresis loss in a D.C. generator ?
Providing laminations in armature core
Providing laminations in stator
Using non-magnetic material for frame
Using material of low hysteresis co-efficient for armature core material

2. Which of the following loss in a D.C. generator is dissipated in the form of heat?
Mechanical loss
Core loss
Copper loss
All of the above

3. 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

4. For constant torque drive which speed control method is preferred ?
Field control
Armature voltage control
Shunt armature control
Mechanical loading system

5. The losses occurring in a D.C. generator are given below. Which loss is likely to have highest proportion at rated load of the generator ?
hysteresis loss
field copper loss
armature copper loss
eddy current loss

6. The hysteresis loss in a D.C. machine least depends on
Frequency of magnetic reversals
Maximum value of flux density
Volume and grade of iron
Rate of flow of ventilating air

7. Which motor should not be started on no-load ?
Series motor
Shunt motor
Cumulatively compounded motor
Differentially compounded motor.

8. If the terminals of armature of D.C. motor are interchanged this action will offer following kind of braking (o) regenerative
plugging
dynamic braking
none of the above
any of the above

9. 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

10. Why are the D.C. motors preferred for traction applications ?
Torque and speed are inversely proportional to armature current
Torque is proportional to armature current
Torque is proportional to square root of armature current
The speed is inversely proportional to the torque and the torque is proportional to square of armature current

11. The plugging gives the
zero torque braking
smallest torque braking
highest torque braking
none of the above

12. Which of the following losses are significantly reduced by laminating the core of a D.C. generator ?
Hysteresis losses
Eddy current losses
Copper losses
Windage losses

13. D.C. motor is to a drive a load which is almost nil for certain part of the load cycle and peak value for short duration. We will select this
series motor
shunt motor
compound motor
any of the above

14. Where D.C. motor of H.P. 12 or more requires frequent starting stopping reversing and speed control
drum type controller is used
three point starter is used
four point starter is used
all above can be used

15. D.C. generators are normally designed for maximum efficiency around
full-load
rated r.p.m.
rated voltage
all of the above

16. The purpose of retardation test on D.C. shunt machines is to find out
stray losses
eddy current losses
field copper losses
windage losses

17. D.C. motor is to drive a load which has certain minimum value for most of the time and some peak value for short duration. We will select the
series motor
shunt motor
compound motor
any of the above

18. 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

19. In the D.C. motor the iron losses occur in
the field
the armature
the brushes
the commutator

20. 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
also runs as a motor comes to stop after sometime

21. The speed of a D.C. shunt motor is required to be more than full load speed. This is possible by
reducing the field current
decreasing the armature current
increasing the armature current
increasing the excitation current

22. If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens
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
nothing will happen to motormotor will come to stop

23. Hopkinson s test on D.C. machines is conducted at
no-load
part load
full-load
overload4

24. The condition for maximum efficiency for a D.C. generator is
eddy current losses = stray losses
hysteresis losses = eddy current losses
copper losses = 0
variable losses = constant losses

25. D.C. generators are installed near the load centres to reduce
iron losses
line losses
sparking
corona losses

26. When the armature of a D.C. motor rotates e.m.f. induced is
self-induced e.m.f.
mutually induced e.m.f.
back e.m.f.
none of the above

27. Which method of braking is generally used in elevators ?
Plugging
Regenerative braking
Rheostatic braking
None of the above

28. Which D.C. motor has got maximum self relieving property ?
Series motor
Shunt motor
Cumulatively compounded motor
Differentially compounded motor

29. In a D.C. generator the iron losses mainly take place in
yoke
commutator
armature conductors
armature rotor