Most Synchronous Motors

51. In a synchronous motor, the breakdown torque is

1. directly proportional to applied voltage
2. directly proportional to the square of the applied voltage
3. inversely proportional to applied voltage
4. none of the above

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52. In a synchronous motor, the damping winding is generally used to

1. prevent hunting and provide the starting torque
2. reduce the eddy currents
3. provide starting torque only
4. reduce noise level

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53. In a synchronous motor, the magnitude of stator back e.m.f. £& depends on

1. d.c. excitation only
2. speed of the motor
3. load on the motor
4. both the speed and rotor flux

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54. In a synchronous motor, the magnitude of stator back e.m.f. Eb depends on

1. load on the motor
2. d.c. excitation only
3. both the speed and rotor flux
4. none of the above

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55. In a synchronous motor, the maximum power developed depends on all of the following except

1. rotor excitation
2. maximum value of coupling angle
3. direction of rotation
4. supply voltage

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56. In a synchronous motor, V-curves represent relation between

1. armature current and field current
2. power factor and speed
3. field current and speed
4. field current and power factor

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57. In case one phase of a three-phase synchronous motor is short-circuited the motor will

1. not start
2. run at 2/3 of synchronous speed
3. run with excessive vibrations
4. take less than the rated load

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58. In which of the following motors the stator and rotor fields rotate simultaneously ?

1. D.C. motor
2. Reluctance motor
3. Universal motor
4. Synchronous motor

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59. In which of the following motors the stator and rotor magnetic field rotate at the same speed ?

1. Universal motor
2. Synchronous motor
3. Induction motor
4. Reluctance motor

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60. Mostly, synchronous motors are of

1. alternator type machines
2. induction type machines
3. salient pole type machines
4. smooth cylindrical type machines

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