Question is ⇒ 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, Options are ⇒ (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, (E) , Leave your comments or Download question paper.

Question is ⇒ 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, Options are ⇒ (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, (E) , Leave your comments or Download question paper. Previous question Next question


Q1.	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 [Wrong Answer]
B.	decreases to half the original value [Wrong Answer]
C.	tends to becomes zero [Wrong Answer]
D.	increases to two times the original value [Correct Answer]
View Answer 5 -5 Explanation:- Answer : D Discuss it below : !! OOPS Login [Click here] is required to post your answer/result Help other students, write article, leave your comments

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⇒ Mostly, synchronous motors are of
alternator type machines
induction type machines
salient pole type machines
smooth cylindrical type machines

⇒ In a synchronous motor, the forced vibrations will be maximum when driving
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a centrifugal pump
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any of the above

⇒ VVhen the rotor speed, in a synchronous machine, becomes more than the synchronous speed during hunting, the damper bars develop
inductor motor torque
induction generator torque
synchronous motor torque
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⇒ A synchronous motor is running on a load with normal excitation. Now if the load on the motor is increased
power factor as well as armature current will decrease
power factor as well as armature current will increase
power factor will increase but armature current will decrease
power factor will decrease and armature current will increase

⇒ The back e.m.f. in the stator of a synchronous motor depends on
number of poles
flux density
rotor speed
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⇒ Dust and dirt accumulation on motor winding will result in
rise in winding temperature
increased core losses
shorting of coils
eddy current flow

⇒ The maximum speed variation in a 3- phase synchronous motor is
10 per cent
6 per cent
4 per cent
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⇒ A synchronous motor can develop synchronous torque
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below or above synchronous speed

⇒ For power factor correction, synchronous motors operate at
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⇒ A synchronous motor will always stop when
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excitation winding gets disconnected
supply voltage frequency changes

⇒ In a synchronous motor, the breakdown torque is
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directly proportional to the square of the applied voltage
inversely proportional to applied voltage
none of the above

⇒ 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
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none of the above

⇒ The coupling angle or load angle of synchronous motor is defined as the angle between the
rotor and stator teeth
rotor and the stator poles of opposite polarity
rotor and the stator poles of the same polarity
none of the above

⇒ The construction of a synchronous motor resembles
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an induction motor
an alternator
a rotary converter

⇒ If load (or torque) angle of a 4-pole synchronous motor is 6° electrical, its value in mechanical degrees is
2
3
4
6

⇒ Which of the following methods is used to start a synchronous motor ?
Damper winding
Star-delta starter
Damper winding in conjunction with star-delta starter
Resistance starter in the armature circuit

⇒ The torque angle, in a synchronous motor, is the angle between
the supply voltage and the back e.m.f.
magnetising current and back e.m.f.
the rotating stator flux and rotor poles
none of the above

⇒ The maximum power developed in a synchronous motor occurs at a coupling angle of
30°
60°
90°
180°

⇒ Which of the following losses, in a synchronous motor, does not vary with load ?
Windage loss
Copper losses
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⇒ Due to which of the following reasons a synchronous motor fails to pull into synchronism after applying D.C. field current ?
High field current
Low short circuit ratio
High core losses
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⇒ If one-phase of a 3-phase synchronous motor is short-circuited, motor
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will overheat in spots
will not come upto speed
will fail to pull into step

⇒ The speed of a synchronous motor
increases as the load increases
decreases as the load decreases
always remains constant
none of the above

⇒ 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
locked-rotor torque
synchronous torque
pull up torque
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⇒ Armature of a synchronous machine is kept fixed because
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armature is associated with large power as compared to the field circuits
of difficulty of providing high voltage insulation on rotor
all of the above reasons

⇒ In which of the following motors the stator and rotor magnetic field rotate at the same speed ?
Universal motor
Synchronous motor
Induction motor
Reluctance motor

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damper winding on stator as well as rotor poles
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⇒ A synchronous motor running with normal excitation adjusts to load increases essentially by increase in
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torque angle

⇒ The net armature voltage of a synchronous motor is equal to the
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arithmetic sum of Eb and V
arithmetic difference of Eb and V
vector difference of Eb and V

⇒ Slip-rings in a synchronous motor carry
direct current
alternating current
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⇒ The percentage slip in case of a synchronous motor is
0.01
1
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