Synchronous Machine MCQs: Multiple Choice Questions

In this section you will find Synchronous Machine MCQs related to Electrical and Electronics.

 

Synchronous Machine MCQs

 

A synchronous motor can develop synchronous torque ?

A. when under loaded
B. while over-excited
C. only at synchronous speed
D. below or above synchronous speed

View Answer

C. only at synchronous speed

 

For power factor correction synchronous motors operate at ?

A. no-load and greatly over-excited fields
B. no-load and under-excited fields
C. normal load with minimum excitation
D. normal load with zero excitation

View Answer

A. no-load and greatly over-excited fields

 

The maximum power developed in the synchronous motor will depend on ?

A. the rotor excitation only
B. the supply voltage only
C. the rotor excitation and supply volt-age both
D. the rotor excitation, supply voltage and maximum value of coupling angle (90°)

View Answer

D. the rotor excitation, supply voltage and maximum value of coupling angle (90°)

 

The percentage slip in case of a synchronous motor is ?

A. 1%
B. 100%
C. 0.5%
D. zero

View Answer

D. zero

 

Slip rings are usually made of ?

A. carbon or graphite
B. brass or steel
C. silver or gold
D. copper or aluminium

View Answer

B. brass or steel

 

Synchronous motors are ?

A. not-self starting
B. self-starting
C. essentially self-starting
D. none of the above

View Answer

A. not-self starting

 

Synchronous motor always runs at ?

A. the synchronous speed
B. less than synchronous speed
C. more than synchronous speed
D. none of the above

View Answer

A. the synchronous speed

 

A synchronous motor can be made self starting by providing ?

A. damper winding on rotor poles
B. damper winding on stator
C. damper winding on stator as well as rotor poles
D. none of the above

View Answer

D. none of the above

 

Synchronous Machine MCQs

 

The power developed by a synchronous motor will be maximum when the load angle is ?

A. zero
B. 45°
C. 90°
D. 120°

View Answer

C. 90°

 

Mostly synchronous motors are of ?

A. alternator type machines
B. induction type machines
C. salient pole type machines
D. smooth cylindrical type machines

View Answer

C. salient pole type machines

 

The armature current of the synchronous motor ?

A. has large values for low excitation only
B. has large values for high excitation only
C. has large values for low and high excitation
D. any of the above

View Answer

C. has large values for low and high excitation

 

The maximum speed variation in a 3-phase synchronous motor is ?

A. 10 per cent
B. 6 per cent
C. 4 per cent
D. 2. per cent
E. zero

View Answer

E. zero

 

The speed of synchronous motor ?

A. increases as the load increases
B. decreases as the load decreases
C. always remains constant
D. none of the above

View Answer

C. always remains constant

 

A synchronous motor working at leading power factor can be used as ?

A. voltage booster
B. phase advancer
C. noise generator
D. mechanical synchronizer

View Answer

B. phase advancer

 

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

View Answer

B. the direction of instantaneous torque reverses after half cycle

 

The construction of a synchronous motor resembles which of the following machine ?

A. a series motor
B. an induction motor
C. an alternator
D. a rotary converter

View Answer

C. an alternator

 

Synchronous Machine MCQs

 

In a synchronous motor, the breakdown torque is ?

A. directly proportional to the square of the applied voltage
B. directly proportional to applied voltage
C. inversely proportional to applied voltage
D. none of the above

View Answer

B. directly proportional to applied voltage

 

The size of a synchronous motor decreases with the increase in ?

A. flux density
B. horse power rating
C. speed
D. all of the above

View Answer

A. flux density

 

The coupling angle or load angle of a synchronous motor is defined as the space angle between ?

A. rotor and stator teeth
B. rotor and the stator poles of opposite polarity
C. rotor and the stator poles of the same polarity
D. none of the above

View Answer

B. rotor and the stator poles of opposite polarity

 

The back e.m.f. in the stator of a synchronous motor depends on ?

A. number of poles
B. flux density
C. rotor speed
D. rotor excitation

View Answer

D. rotor excitation

 

If the field of synchronous motor is under excited the power factor will be ?

A. zero
B. unity
C. lagging
D. leading

View Answer

C. lagging

 

In a synchronous motor, V-curves represent relation between ?

A. armature current and field current
B. power factor and speed
C. field current and speed
D. field current and power factor

View Answer

A. armature current and field current

 

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

View Answer

B. increases with increase in its excitation

 

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

View Answer

C. providing damper bars in the rotor pole faces

 

Synchronous Machine MCQs

 

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

View Answer

D. lagging, leading and unity power factors

 

In a synchronous motor the magnitude of stator back emf depends on ?

A. d.c. excitation only
B. speed of the motor
C. load on the motor
D. both the speed and rotor flux

View Answer

A. d.c. excitation only

 

The back e.m.f. of a synchronous motor depends on ?

A. speed
B. load
C. load angle
D. all of the above

View Answer

C. load angle

 

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 causing more motor current

View Answer

B. the rotor by shifting its phase backward causes motor to take more current

 

The shaft of synchronous motor is made of ?

A. mild steel
B. chrome steel
C. alnico
D. stainless steel

View Answer

A. mild steel

 

A synchronous motor can be started by ?

A. pony motor
B. D.C. compound motor
C. providing damper winding
D. any of the above

View Answer

D. any of the above

 

A pony motor is basically a ?

A. small induction motor
B. D.C. series motor
C. D.C. shunt motor
D. double winding A.C./D.C. motor

View Answer

A. small induction motor

 

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

View Answer

D. over-excited

Synchronous Machine MCQs

 

The armature current of the synchronous motor has higher values for ?

A. high excitation only
B. low excitation only
C. both (A) and (B)
D. none of the above

View Answer

C. both (A) and (B)

 

If one phase of a 3 phase synchronous motor is short circuited the motor will ?

A. will refuse to start
B. will overheat in spots
C. will not come upto speed
D. will fail to pull into step

View Answer

A. will refuse to start

 

In a three phase synchronous motor the magnitude of field flux ?

A. varies with power factor
B. varies with speed
C. varies with the load
D. remains constant at all loads

View Answer

D. remains constant at all loads

 

In the synchronous motor rotor copper losses are met by ?

A. d.c. source
B. armature input
C. motor input
D. supply lines

View Answer

A. d.c. source

 

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

View Answer

D. field current and armature current

 

An over-excited synchronous motor takes ?

A. leading current
B. lagging current
C. both (A) and (B)
D. none of the above

View Answer

A. leading current

 

The synchronous motor is not inherently self-starting because ?

A. the force required to accelerate the rotor to the synchronous speed in an instant is absent
B. the starting device to accelerate the rotor to near synchronous speed is absent
C. a rotating magnetic field does not have enough poles
D. the rotating magnetic field is produced by only 50 Hz frequency currents

View Answer

A. the force required to accelerate the rotor to the synchronous speed in an instant is absent

 

A three-phase synchronous motor will have ?

A. no slip-rings
B. one slip-ring
C. two slip-rings
D. three slip-rings

View Answer

C. two slip-rings

 

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

View Answer

A. not start

 

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