Question 1

If the synchronous motor, properly synchronised to the supply is running on no load and is having negligible loss then

Accepted Answer

A)  the stator current will be zero
B)  the stator current will be very small
C)  the stator current will be very high
D)  the back e.m.f. will be more than the supply voltageE) B) and D)
F) All of the above A

Question 2

Which of the following losses is not dissipated by the stator core surface in a synchronous motor ?

Accepted Answer

A)  Eddy current losses in the conductors
B)  Iron losses in the stator
C)  Copper losses in the slot portion of the conductors
D)  Windage lossesE) None of the above
F) B) and D)

Question 3

For power factor correction, synchronous motors operate at

Accepted Answer

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 excitationE) B) and D)
F) None of the above

Question 4

A synchronous motor which works on a leading power factor and does not drive a mechanical load is called as

Accepted Answer

A)  static condenser
B)  condenser
C)  synchronous condenser
D)  none of the aboveE) A) and D)
F) B) and C)

Question 5

A synchronous machine with low value of short-circuit ratio has

Accepted Answer

A)  lower stability limit
B)  high stability limit
C)  good speed regulation
D)  good voltage regulationE) A) and D)
F) None of the above

Question 6

The maximum torque which a synchronous motor will develop at rest for any angular position of the rotor, at rated stator supply voltage and frequency, is known as

Accepted Answer

A)  locked-rotor torque
B)  synchronous torque
C)  pull up torque
D)  reluctance torqueE) B) and C)
F) All of the above

Question 7

If the field of a synchronous motor is underexcited, the power factor will be

Accepted Answer

A)  zero
B)  unity
C)  lagging
D)  leadingE) B) and C)
F) A) and B)

Question 8

Which of the following losses, in a synchronous motor, does not vary with load?

Accepted Answer

A)  Windage loss
B)  Copper losses
C)  Any of the above
D)  None of the aboveE) None of the above
F) C) and D) A

Question 9

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

Accepted Answer

A)  number of poles
B)  flux density
C)  rotor speed
D)  rotor excitationE) None of the above
F) B) and C)

Question 10

The armature current of the synchronous motor

Accepted Answer

A)  has large values for low excitation i niy
B)  has large values for high excitation only
C)  has large values for low and high excitation
D)  any of the aboveE) B) and D)
F) A) and C) C

Question 11

The maximum value of torque that a synchronous motor can develop without losing its synchronism, is known as

Accepted Answer

A)  slip torque
B)  pull-out torque
C)  breaking torque
D)  synchronising torqueE) A) and D)
F) B) and C)

Question 12

In a synchronous motor, the armature current has large values for

Accepted Answer

A)  high excitation only
B)  low excitation only
C)  both high and low excitation
D)  none of the aboveE) A) and D)
F) None of the above

Question 13

The duration of sudden snort-circuit test on a synchronous motor is usually about

Accepted Answer

A)  one hour
B)  one minute
C)  one second
D)  none of the aboveE) B) and C)
F) None of the above

Question 14

The construction of a synchronous motor resembles

Accepted Answer

A)  a series motor
B)  an induction motor
C)  an alternator
D)  a rotary converterE) A) and C)
F) None of the above

Question 15

In a synchronous motor, the breakdown torque is

Accepted Answer

A)  directly proportional to applied voltage
B)  directly proportional to the square of the applied voltage
C)  inversely proportional to applied voltage
D)  none of the aboveE) A) and C)
F) All of the above

Question 16

Exciters of synchronous machines are

Accepted Answer

A)  d.c. shunt machines
B)  d.c. series machines
C)  d.c. compound machines
D)  any of the aboveE) A) and B)
F) B) and C)

Question 17

The maximum power developed in a synchronous motor will depend on

Accepted Answer

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°) E) B) and D)
F) All of the above

Question 18

If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will

Accepted Answer

A)  stop
B)  run as induction motor
C)  function as static condenser
D)  burn with dense smokeE) A) and D)
F) All of the above

Question 19

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

Accepted Answer

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 aboveE) B) and C)
F) A) and D)

Question 20

A synchronous motor develops maximum power when load angle is

Accepted Answer

A)  45°
B)  60°
C)  90°
D)  120°E) A) and C)
F) B) and C)

Exam 5: Synchronous Motor: Power Factor, Back EMF, Torque, Losses

If the synchronous motor, properly synchronised to the supply is running on no load and is having negligible loss then

Correct AnswerverifiedA

Which of the following losses is not dissipated by the stator core surface in a synchronous motor ?

Correct AnswerverifiedShow Answer

For power factor correction, synchronous motors operate at

Correct AnswerverifiedShow Answer

A synchronous motor which works on a leading power factor and does not drive a mechanical load is called as

Correct AnswerverifiedShow Answer

A synchronous machine with low value of short-circuit ratio has

Correct AnswerverifiedShow Answer

The maximum torque which a synchronous motor will develop at rest for any angular position of the rotor, at rated stator supply voltage and frequency, is known as

Correct AnswerverifiedShow Answer

If the field of a synchronous motor is underexcited, the power factor will be

Correct AnswerverifiedShow Answer

Which of the following losses, in a synchronous motor, does not vary with load?

Correct AnswerverifiedA

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

Correct AnswerverifiedShow Answer

The armature current of the synchronous motor

Correct AnswerverifiedC

The maximum value of torque that a synchronous motor can develop without losing its synchronism, is known as

Correct AnswerverifiedShow Answer

In a synchronous motor, the armature current has large values for

Correct AnswerverifiedShow Answer

The duration of sudden snort-circuit test on a synchronous motor is usually about

Correct AnswerverifiedShow Answer

The construction of a synchronous motor resembles

Correct AnswerverifiedShow Answer

In a synchronous motor, the breakdown torque is

Correct AnswerverifiedShow Answer

Exciters of synchronous machines are

Correct AnswerverifiedShow Answer

The maximum power developed in a synchronous motor will depend on

Correct AnswerverifiedShow Answer

If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedShow Answer

A synchronous motor develops maximum power when load angle is

Correct AnswerverifiedShow Answer

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