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Free download in PDF Synchronous Motor Objective Type Questions and Answers for competitive exams. These short objective type questions with answers are very important for Board exams as well as competitive exams. These short solved questions or quizzes are provided by Gkseries.
(21)
The standard full-load power factor ratings for synchronous motors are
[A]
Zero or 0.8 leading
[B]
Unity or 0.8 lagging
[C]
Unity or 0.8 leading
[D]
Unity or zero
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
[A]
Synchronizing
[B]
Torque
[C]
Power factor
[D]
Slip
(23)
An electric motor in which both the rotor and stator fields rotates with the same speed is called aa/an ....... motor
[A]
D.C.
[B]
Charge
[C]
Synchronous
[D]
Universal
(24)
The maximum power developed in a synchronous motor occurs at a coupling angle of
[A]
30 degree
[B]
90 degree
[C]
60 degree
[D]
180 degree
(25)
The minimum armature current of the synchronous motor corresponds to operation at
[A]
Zero power factor leading
[B]
Unity power factor
[C]
0.707 power factor lagging
[D]
0.707 power factor leading
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
[A]
More
[B]
Less
[C]
Equal
[D]
Twice
(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
[A]
Leading p.f. with under-excitation
[B]
Leading p.f. with over-excitation
[C]
Lagging p.f. with over-excitation
[D]
No change of p.f.
Answer: Leading p.f. with over-excitation
(28)
The standard full-load power factor ratings for synchronous motors are
[A]
Zero or 0.8 leading
[B]
Unity or 0.8 lagging
[C]
Unity or 0.8 leading
[D]
Unity or zero
Answer: Unity or 0.8 leading
(29)
As the load is applied to 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.m.f. decreases causing an increase in motor current
[D]
The rotor strengthens the rotating field causing more motor current
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
[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 but armature current will increase
Answer: Power factor will decrease but armature current will increase
31
A synchronous machine with large air gap has
[A]
A higher value of stability limit
[B]
A small value of inherent regulation
[C]
A higher synchronizing power which makes the machine less sensitive to load variations
[D]
All of the above
32
The oscillations in a synchronous motor can be damped out by
[A]
Maintaining constant excitation
[B]
Running the motor on leading power factors
[C]
Providing damper bars in the rotor poles faces
[D]
Oscillations cannot be damped
Answer: Providing damper bars in the rotor poles faces
33
Under which of the following conditions hunting of synchronous motor is likely to occur
[A]
Periodic variation of load
[B]
Over-excitation
[C]
Over-loading for long periods
[D]
Small and constant load
Answer: Periodic variation of load
34
As the load is applied to 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.m.f. decreases causing an increase in motor current
[D]
The rotor strengthens the rotating field causing more motor current
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
[A]
Under-loaded
[B]
Over-loaded
[C]
Under-excited
[D]
Over-excited
36
Hunting in a synchronous motor takes place
[A]
When supply voltage fluctuates
[B]
When load varies
[C]
When power factor is unity
[D]
Motor is under loaded
37
The shaft of synchronous motor is made of
[A]
Mild steel
[B]
Chrome steel
[C]
Alnico
[D]
Stainless steel
38
The percentage slip in case of a synchronous motor is
[A]
1%
[B]
100%
[C]
0.5%
[D]
Zero
39
A synchronous motor working at leading power factor can be used as
[A]
Voltage booster
[B]
Phase advancer
[C]
Noise generator
[D]
Mechanical synchronizer
40
A synchronous motor will always stop when
[A]
Supply voltage fluctuates
[B]
Load in motor varies
[C]
Excitation winding gets disconnected
[D]
Supply voltage frequency changes
Answer: Excitation winding gets disconnected
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