Questions
21
The standard full-load power factor ratings for synchronous motors are
Answer: Unity or 0.8 leading
22
The angle between the synchronously-roating stator flux and rotor poles of a synchronous motor is called....... angle
Answer: Torque
23
An electric motor in which both the rotor and stator fields rotates with the same speed is called aa/an ....... motor
Answer: Synchronous
24
The maximum power developed in a synchronous motor occurs at a coupling angle of
Answer: 90 degree
25
The minimum armature current of the synchronous motor corresponds to operation at
Answer: Unity power factor
26
When load on an over-excited or under-excited synchronous motor is increased, rate of change of its armature current as compared with that of power factor is
Answer: Less
27
A synchronous motor connected to infinite bus-bars has at constant full-load, 100% excitation and unity p.f. on changing the excitation only, the armature current will have
Answer: Leading p.f. with over-excitation
28
The standard full-load power factor ratings for synchronous motors are
Answer: Unity or 0.8 leading
29
As the load is applied to synchronous motor, the motor takes more armature current because
Answer: The rotor by shifting its phase backward causes motor to take more current
30
A synchronous motor is running on a load with normal excitation. Now if the load on the motor is increased
Answer: Power factor will decrease but armature current will increase
32
The oscillations in a synchronous motor can be damped out by
Answer: Providing damper bars in the rotor poles faces
33
Under which of the following conditions hunting of synchronous motor is likely to occur
Answer: Periodic variation of load
34
As the load is applied to synchronous motor, the motor takes more armature current because
Answer: The rotor by shifting its phase backward causes motor to take more current
35
A synchronous motor can be used as a synchronous capacitor when it is
Answer: Over-excited
39
A synchronous motor working at leading power factor can be used as
Answer: Phase advancer
40
A synchronous motor will always stop when
Answer: Excitation winding gets disconnected
