Synchronous Motor Quiz | Synchronous Motor Multiple Choice Questions and Answers

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Questions
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

Answer: 90 degree
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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

Answer: Leading current
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

Answer: 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

Answer: The motor stops
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

Answer: 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

Answer: Lagging
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

Answer: 90
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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