D.C. Machines

51. The angle between the synchronous rotating stator flux and rotor poles of a synchronous motor is

1. Synchronizing angle
2. Torque angle
3. Power factor angle
4. Slip angle

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52. The basic requirement of a dc armature winding is that it must be

1. a closed one
2. a lap winding
3. a wave winding
4. either b or c

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53. The commutation process in a dc generator basically involves

1. passage of current from moving armature to a stationary load
2. reversal of current in an armature coil as it crosses MNA
3. conversion of ac to dc
4. suppression of reactance voltage

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54. The counter emf of dc motor

1. Often exceeds the supply voltage
2. Aids the applied voltage
3. Helps in energy conversion
4. Regulates its armature voltage

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55. The crawling in an induction motor is caused by

1. improper design of the machine
2. low voltage supply
3. high loads
4. harmonics developed in the motor Ans = D

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56. The critical resistance of the dc generator is the resistance of

1. armature
2. field
3. load
4. brushes

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57. In a 3-phase synchronous motor

1. the speed of stator MMF is always more than that of rotor MMF.
2. the speed of stator MMF is always less than that of rotor MMF.
3. the speed of stator MMF is synchronous speed while that of rotor MMF is zero.
4. rotor and stator MMF are stationary with respect to each other.

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58. The current from the stator of an alternator is taken out to the external load circuit through

1. slip rings.
2. commutator segments.
3. solid connections.
4. carbon brushes.

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59. The D.C. series motor should always be started with load because

1. at no load, it will rotate at dangerously high speeD.
2. it will fail to start.
3. it will not develop high starting torque.
4. all are true.

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60. The DC motor, which can provide zero speed regulation at full load without any controller is

1. Series
2. Shunt
3. Cumulative Compound
4. Differential Compound

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