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Free download in PDF Synchronous Motor Multiple Choice 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.
(1)
Synchronous motor always runs at
[A]
The synchronous speed
[B]
Less than synchronous speed
[C]
More than synchronous speed
[D]
None of the above
Answer: The synchronous speed
(2)
The power development by a synchronous motor will be maximum when the load angle is
[A]
Zero
[B]
45 degree
[C]
90 degree
[D]
120 degree
(3)
A synchronous machine is called a doubly excited machine because
[A]
It can be overexcited
[B]
It has two sets of rotor poles
[C]
Both its rotor and sator are excited
[D]
It needs twice the normal exciting current
Answer: Both its rotor and sator are excited
(4)
Mostly, synchronous motors are of
[A]
Alternator type machines
[B]
Induction type machines
[C]
Salient pole type machines
[D]
Smooth cylindrical type machines
Answer: Salient pole type machines
(5)
A synchronous motor can be started by
[A]
Pony Motor
[B]
D.C. compound winding
[C]
Providing damper winding
[D]
None of the above
Answer: None of the above
(6)
Ignoring the effects of armature reaction, if excitation of a synchronous motor running with constant load is decreased from its normal value, it leads to
[A]
Increase in but decrease in Eb
[B]
Increase in Eb but decrease in Ia
[C]
Increase in both Ia and p.f. which is lagging
[D]
Increase in both Ia and SYMBOL
Answer: Increase in both Ia and SYMBOL
(7)
An over-excited synchronous motor takes
[A]
Leading current
[B]
Lagging current
[C]
Both (a) and (b)
[D]
None of the above
(8)
A synchronous motor running with normal excitation adjusts to load increases essentially by increase in its
[A]
Power factor
[B]
Torque angle
[C]
Back e.m.f.
[D]
Armature current
(9)
An over-excited synchronous motor is used for
[A]
Fluctuating loads
[B]
Variable speed loads/span>
[C]
Low torque loads
[D]
Power factor corrections
Answer: Power factor corrections
(10)
When the excitation of an unloaded salient pole synchronous motor suddenly gets disconnected
[A]
The motor stops
[B]
It runs as a reluctance motor at the same speed
[C]
It runs as a reluctance motor at a lower speed
[D]
None of the above
(11)
When load on a normally-excited synchronous motor is increased, its power factor tends to
[A]
Approach unity
[B]
Becomes increasingly lagging
[C]
Becomes increasingly leading
[D]
Remain unchanged
Answer: Becomes increasingly lagging
(12)
When running under no-load condition and with normal excitation, armature current Ia drawn by a synchronous motor
[A]
Leads the back e.m.f.Eb by a small angle
[B]
Is large
[C]
Lags the applied voltage V by a small angle
[D]
Lags the resultant voltage ER by 90 degree
Answer: Lags the applied voltage V by a small angle
(13)
When load on a synchronous motor running with normal excitation is increased, armature current drawn by it increases because
[A]
Back e.m.f. Eb becomes less than applied voltage V
[B]
Power factor is decreased
[C]
Net resultant voltage ER in armature is increased
[D]
Motor speed is reduced
Answer: Net resultant voltage ER in armature is increased
(14)
When load on a synchronous motor is increased, its armature currents in increased provided it is
[A]
Normally-excited
[B]
Over-excited
[C]
Under-excited
[D]
All of the above
(15)
The effect of increasing load on a synchronous motor running with normal excitation is to
[A]
Increase both its Ia and p.f.
[B]
Decrease Ia but increase p.f.
[C]
Increase Ia but decrease p.f.
[D]
Decrease both its Ia and p.f.
Answer: Increase Ia but decrease p.f.
(16)
The V-curves of a synchronous motor show relationship between
[A]
Excitation current and back e.m.f
[B]
Field current and p.f.
[C]
D.C. field current and A.C. armature current
[D]
Armature current and supply voltage
Answer: D.C. field current and A.C. armature current
(17)
If the field of a synchronous motor is under excited, the power factor will be
[A]
Lagging
[B]
Leading
[C]
Unity
[D]
More than unity
(18)
The maximum value of torque angle a in a synchronous motor is .......... degrees electrical
[A]
45
[B]
90
[C]
Between 45 and 90
[D]
Below 60
(19)
In a synchronous motor, the magnitude of stator back e.m.f. Eb depends on
[A]
Speed of the motor
[B]
Load of the motor
[C]
Both the speed and rotor flux
[D]
D.C. excitation only
Answer: D.C. excitation only
(20)
The direction of rotation of a synchronous motor can be reversed by reversing
[A]
Current to the field winding
[B]
Supply phase sequence
[C]
Polarity of rotor poles
[D]
None of the above
Answer: Supply phase sequence
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