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MCQ of Electrical Machines page-2

21. The rotation of wound-rotor induction motor can be reversed by

(a) Transposing any two leads from the slip rings.
Transposing any two line leads.
(c) None of the above

22. A split-phase motor has high stating torque.

(a) true.
false

23. The direction of rotation of a split phase motor can be reversed

(a) By reversing the leads of main winding.
(b) By reversing the leads of auxiliary winding.
(a) and (b) both are true.
(d) None of the above

24. The capacitor-start motor has a high starting torque.

true.
(b) false

25. A universal motor can be run either on a.c. or d.c.

true.
(b) false

26. The phase relationship between the primary and secondary voltages of a transformer is

(a) 90 degrees out of phase.
(b) In the same phase.
180 degrees out of phase.
(d) None of the above

27. For point starter in the d.c. motor is used

(a) To increase the field current.
(b) To decrease the field current.
Not to affect the current passing through HOLD ON coil even if any change in the field current takes place.
(d) None of above

28.Which of the following motor is used in the locomotives motor drives?

(a) A.C. series motor.
(b) Induction motor.
D.C. series motor.
(d) Synchronous motor

29. Which of the following motors has high starting torque ?

(a) D.C. shunt motor.
(b) Squirrel cage induction motor.
D.C. series motor.
(d) A.C. series motor

30. The efficiency of d.c. shunt generator is maximum when

(a) Magnetic losses are equal to mechanical losses.
Armature copper losses are equal to constant losses.
(c) Field copper losses are equal to constant losses.
(d) Stray losses are equal to copper losses

31. In the case of d.c. shunt generation, the shunt copper loss, is practically constant.

true.
(b) false

32. Armature reaction is attributed to

(a) The effect of magnetic field set up field current.
The effect of the magnetic field set up by armature current.
(c) The effect of the magnetic field set up by back e.m.f.
(d) None of the above

33. The dummy coil in the d.c. machines is used to

(a) Eliminate armature reaction.
Bring out mechanical balance of armature.
(c) Eliminate reactance voltage.
(d) None of above

34. Equilizer rings in the d.c. in the d.c. generator (lap winding ) are used

To avoid unequal distribution of current at the brushes there by helping to get sparkles commutation.
(b) To avoid harmonics developed in the machine.
(c) To avoid noise developed in the machine.
(d) To avoid overhang

35. The speed of the d.c. motor decreases as the flux in the field winding decreases.

(a) True.
false

36. The sparking at the brushes in the d.c. generator is attributed to

(a) quick reversal of current in the coil under commutation.
(b) Armature reaction.
Reactance voltage.
(d) High resistance of the brushes

37. Interpoles in the armature of d.c generator are used

(a) To neutralize the reactance voltage only.
To neutralize the reactance voltage and cross-magnetizing effect of armature reaction.
(c) To neutralize the cross-magnetizing effect of armature reaction only.
(d) None of the above

38. The transformer is not used in the d.c. line because

(a) There is no need to step up the d.c. voltage.
(b) Losses in the d.c. circuit are high.
Faraday`s law is not valid as the rate of change of flux is zero.
(d) Harmonics developed in the transformer will cause distortion in the voltage

39. The transformer is analogous to gear trains.

true.
(b) false

40. The d.c. shunt generators are not suited for parallel operation because of their slightly drooping voltage characteristics.

(a) true.
false

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