Explore topic-wise MCQs in Electrical Engineering Questions.

This section includes 122 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Engineering Questions knowledge and support exam preparation. Choose a topic below to get started.

51.

In a synchronous motor, the magnitude of stator back e.m.f. Eb depends on___________?
A. load on the motor
B. d.c. excitation only
C. both the speed and rotor flux
D. none of the above
Answer» C. both the speed and rotor flux
Discussion
52.

The rotor copper losses, in a synchronous motor, are met by____________?
A. d.c. source
B. armature input
C. motor input
D. supply lines
Answer» B. armature input
Discussion
53.

The effect of increasing the load on a synchronous motor running with normal excitation is to___________?
A. decrease both armature current and power factor
B. decrease armature current but increase power factor
C. increase armature current but decrease power factor
D. increase both its armature current and power factor
Answer» D. increase both its armature current and power factor
Discussion
54.

The induced e.m.f. in a synchronous motor working on leading power factor will be_____________?
A. more than the supply voltage
B. less than the supply voltage
C. equal to the supply voltage
D. None of these
Answer» B. less than the supply voltage
Discussion
55.

Hunting in a synchronous motor cannot be due to___________?
A. windage friction
B. variable load
C. variable frequency
D. variable supply voltage
Answer» B. variable load
Discussion
56.

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» D. unity or zero
Discussion
57.

The speed regulation of a synchronous motor is always___________?
A. 1%
B. 0.5%
C. positive
D. zero
Answer» E.
Discussion
58.

Which of the following methods is used to start a synchronous motor?
A. Damper winding
B. Star-delta starter
C. Damper winding in conjunction with star-delta starter
D. Resistance starter in the armature circuit
Answer» D. Resistance starter in the armature circuit
Discussion
59.

An over excited synchronous motor is used for____________?
A. fluctuating loads
B. variable speed loads
C. low torque loads
D. power factor corrections
Answer» E.
Discussion
60.

In a synchronous motor which loss varies with load ?
A. Windage loss
B. Bearing friction loss
C. Copper loss
D. Core loss
Answer» D. Core loss
Discussion
61.

For V-curves for a synchronous motor the graph is drawn between:_______________?
A. armature current and power factor
B. terminal voltage and load factor
C. power factor and field current
D. field current and armature current
Answer» E.
Discussion
62.

To limit the operating temperature an electrical machine should have proper____________?
A. voltage rating
B. current rating
C. power factor
D. speed
Answer» C. power factor
Discussion
63.

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
Answer» E.
Discussion
64.

In a synchronous motor running with fixed excitation, when the load is increased three times, its torque angle becomes approximately
A. one-third
B. twice
C. thrice
D. six times
E. nine times
Answer» D. six times
Discussion
65.

In which of the following motors the stator and rotor fields rotate simultaneously?
A. D.C. motor
B. Reluctance motor
C. Universal motor
D. Synchronous motor
E. Induction motor
Answer» E. Induction motor
Discussion
66.

Synchronous motors are_____________?
A. not-self starting
B. self-starting
C. essentially self-starting
D. none of the above
Answer» B. self-starting
Discussion
67.

If the field circuit of an unloaded salientpole synchronous motor gets suddenly open-circuited, then
A. it runs at a slower speed
B. the motor stops
C. it continues to run at the same speed
D. it runs at a very high speed
Answer» C. it continues to run at the same speed
Discussion
68.

Synchronsizing power of a synchronous machine is_____________?
A. direcly proportional to the synchronous reactance
B. inversely proportional to the synchronous reactance
C. equal to the synchronous reactance
D. none of the above
Answer» C. equal to the synchronous reactance
Discussion
69.

If in a synchronous motor, driving a given mechanical load and drawing current at a leading power factor from constant voltage supply its field excitation is increased, its power factor
A. will become more
B. will become less
C. will remain unchanged
D. none of the above
Answer» C. will remain unchanged
Discussion
70.

A synchronous motor is running with normal excitation. When the load is increased, the armature current drawn by it increases because
A. speed of the motor is reduced
B. power factor is decreased
C. Eb (back e.m.f.) becomes less than V (applied voltage)
D. Er (net resultant voltage) in armature is increased
E. none of the above
Answer» E. none of the above
Discussion
71.

Stability of a synchronous machine:
A. decreases with increase in its excitation
B. increases with increase in its excitation
C. remains unaffected with increase in excitation
D. any of the above
Answer» C. remains unaffected with increase in excitation
Discussion
72.

If excitation of a synchronous motor running with a constant load is decreased from its normal value, ignoring effects of armature reaction, it leads to____________?
A. increase in both armature current and power factor angle
B. increase in back e.m.f. but decrease in armature current
C. increase in both armature current and power factor which is lagging
D. increase in torque angle but decrease in back e.m.f.
Answer» B. increase in back e.m.f. but decrease in armature current
Discussion
73.

While starting a salient pole synchronous motor by induction motor action and connecting field discharge resistance across field, starting and accelerating torque is produced by_____________?
A. induction motor torque in field winding
B. induction motor torque in damper winding
C. eddy current and hysteresis torque in pole faces
D. reHetance motor torque due to saliency of the rotor
E. all of the above methods
Answer» F.
Discussion
74.

A synchronous motor installed at the receiving end substation operates with such an excitation that it takes power at lagging power factor. Now if the applied voltage of the synchronous motor goes down, the power factor of the synchronous motor will___________?
A. remain same
B. go down
C. improve
D. none of the above
Answer» D. none of the above
Discussion
75.

Which of the following motors will be used in electric clocks?
A. D.C. shunt motor
B. D.C. series motor
C. A.C. induction motor
D. A.C. synchronous motor
Answer» E.
Discussion
76.

The speed of a synchronous motor:
A. increases as the load increases
B. decreases as the load decreases
C. always remains constant
D. none of the above
Answer» D. none of the above
Discussion
77.

When a 3-phase synchronous generator is supplying a zero power factor lagging load, the armature field affects the main field in the following way
A. augments it directly
B. directly opposes it
C. cross-magnetises it
D. none of the above
Answer» C. cross-magnetises it
Discussion
78.

Which of the following resistances can be measured by conducting insulation resistance test on a synchronous motor ?
A. Phase to phase winding resistance
B. Stator winding to earthed frame
C. Rotor winding to earthed shaft
D. All of the above
Answer» E.
Discussion
79.

The mechanical displacement of the rotor with respect to the stator, in polyphase multipolar synchronous motors running at full load, is of the order of_____________?
A. zero degree
B. two degrees
C. five degrees
D. ten degrees
Answer» D. ten degrees
Discussion
80.

An important advantage of a synchronous motor over wound round induction motor is that
A. its power factor may be varied at will
B. its speed is independent of supply frequency
C. its speed may be controlled more easily
D. none of the above
Answer» B. its speed is independent of supply frequency
Discussion
81.

If in a synchronous motor, driving mechanical load and drawing current at lagging power factor from constant voltage supply, its field excitation is increased, then its power factor__________?
A. become more
B. become less
C. remain constant
D. none of the above
Answer» C. remain constant
Discussion
82.

Change of D.C. excitation of a synchronous motor changes:
A. applied voltage of the motor
B. power factor of power drawn by the motor
C. motor speed
D. none of the these
E. all of the these
Answer» C. motor speed
Discussion
83.

Riunting 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
Answer» C. when power factor is unity
Discussion
84.

The percentage slip in case of a synchronous motor is____________?
A. 1%
B. 100%
C. 0.5%
D. zero
Answer» E.
Discussion
85.

The angle between the rotating stator flux and rotor poles is called _________ angle.
A. synchronizing
B. obtuse
C. torque
D. power factor
Answer» D. power factor
Discussion
86.

Slip-rings in a synchronous motor carry____________?
A. direct current
B. alternating current
C. no current
D. all of the above
Answer» B. alternating current
Discussion
87.

When the stator windings are connected in such a fashion that the number of poles are made half, the speed of the rotor of a synchronous motor___________?
A. remains same as the original value
B. decreases to half the original value
C. tends to becomes zero
D. increases to two times the original value
Answer» E.
Discussion
88.

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
Answer» C. equal
Discussion
89.

A synchronous motor can operate at____________?
A. lagging power factor only
B. leading power factor only
C. unity power factor only
D. lagging, leading and unity power factors
Answer» E.
Discussion
90.

When the field of a synchronous motor is under-excited, the power factor will be____________?
A. leading
B. lagging
C. unity
D. zero
Answer» C. unity
Discussion
91.

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 pole faces
D. oscillations cannot be damped
Answer» D. oscillations cannot be damped
Discussion
92.

The power developed by a synchronous motor will be maximum when the load angle is____________?
A. zero
B. 45°
C. 90°
D. 120°
Answer» D. 120°
Discussion
93.

If load (or torque) angle of a 4-pole synchronous motor is 6° electrical, its value in mechanical degrees is__________?
A. 2
B. 3
C. 4
D. 6
Answer» C. 4
Discussion
94.

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» C. 0.707 power factor lagging
Discussion
95.

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» B. less than synchronous speed
Discussion
96.

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» B. Over-excitation
Discussion
97.

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.m.f. decreases causing an increase in motor current
D. the rotor strengthens the rotating field casuing more motor current
Answer» C. the back e.m.f. decreases causing an increase in motor current
Discussion
98.

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
Answer» E.
Discussion
99.

Synchronous motors are generally not self-starting because:
A. the direction of rotation is not fixed
B. the direction of instantaneous torque reverses after half cycle
C. startes cannot be used on these machines
D. starting winding is not provided on the machines
Answer» C. startes cannot be used on these machines
Discussion
100.

In case one phase of a three-phase synchronous motor is short-circuited the motor will____________?
A. not start
B. run at 2/3 of synchronous speed
C. run with excessive vibrations
D. take less than the rated load
Answer» B. run at 2/3 of synchronous speed
Discussion