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Electrical Engineering Objective Questions { Synchronous Motors }

50. When V is the applied voltage, then the breakdown torque of a synchronous motor varies as
A. V
B. V312
C. V2
D. 1/V

51. The power developed by a synchronous motor will be maximum when the load angle is
A. zero
D. 120?

52. A synchronous motor can be used as a synchronous capacitor when it is
A. under-loaded
B. over-loaded
C. under-excited
D. over-excited

53. A synchronous motor is running on a load with normal excitation. Now if the load on the motor is increased
A. power factor as well as armature current will decrease
B. power factor as well as armature current will increase
C. power factor will increase but armature current will decrease
D. power factor will decrease and armature current will increase

54. Mostly, synchronous motors are of
A. alternator type machines
B. induction type machines
C. salient pole type machines
D. smooth cylindrical type machines

55.  The synchronous motor is not inherently self-starting because
A. the force required to accelerate the rotor to the synchronous speed in an instant is absent
B. the starting device to accelerate the rotor to near synchronous speed is absent
C. a rotating magnetic field does not have enough poles
D. the rotating magnetic field is produced by only 50 Hz frequency currents

56.  As the load is applied to a synchronous motor, the motor takes more armature current because
A. the increased load has to take more current
B. the rotor by shifting its phase backward causes motor to take more current
C. the back e.mi decreases causing an increases in motor current
D. the rotor strengthens the rotating field causing more motor current

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