Question is ⇒ In case one phase of a three-phase synchronous motor is short-circuited the motor will, Options are ⇒ (A) not start, (B) run at 2/3 of synchronous speed, (C) run with excessive vibrations, (D) take less than the rated load, (E) , Leave your comments or Download question paper.

Question is ⇒ In case one phase of a three-phase synchronous motor is short-circuited the motor will, Options are ⇒ (A) not start, (B) run at 2/3 of synchronous speed, (C) run with excessive vibrations, (D) take less than the rated load, (E) , Leave your comments or Download question paper. Previous question Next question


Q1.	In case one phase of a three-phase synchronous motor is short-circuited the motor will
A.	not start [Correct Answer]
B.	run at 2/3 of synchronous speed [Wrong Answer]
C.	run with excessive vibrations [Wrong Answer]
D.	take less than the rated load [Wrong Answer]
View Answer 6 -1 Explanation:- Answer : A 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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⇒ An over-excited synchronous motor takes
leading current
lagging current
both (a) and (b)
none of the above

⇒ The efficiency of a properly designed synchronous motor will usually fall in range
60 to 70%
75 to 80%
85 to 95%
99 to 99.5%

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

⇒ If in a synchronous motor, driving mechanical load and drawing current at lagging power factor from constant voltage supply, its field excita.6.on is increased, then its power factor
become more
become less
remain constant
none of the above

⇒ In a synchronous motor which loss varies with load ?
Windage loss
Bearing friction loss
Copper loss
Core loss

⇒ A synchronous motor working at leading power factor can be used as
voltage booster
phase advancer
noise generator
mechanical synchronizer

⇒ The armature current of the synchronous motor has higher values for
high excitation only
low excitation only
both (a) and (b)
none of the above

⇒ To limit the operating temperature an electrical machine should have proper
voltage rating
current rating
power factor
speed

⇒ The maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as
pull-up torque
pull-in torque
pull-out torque
none of the above

⇒ A synchronous motor which works on a leading power factor and does not drive a mechanical load is called as
static condenser
condenser
synchronous condenser
none of the above

⇒ A rotory converter can also be run as a
d.c. shunt motor
d.c. series motor
d.c. compound motor
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⇒ When the excitation of an unloaded salient pole synchronous motor suddenly gets disconnected
the motor stops
it runs as a reluctance motor at the same speed
it runs as a reluctance motor at a lower speed
none of the above

⇒ The back e.m.f. of a synchronous motor depends on
speed
load
load angle
all of the above

⇒ A synchronous motor can be started by
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providing damper winding
any 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
will become more
will become less
will remain unchanged
none of the above

⇒ 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
remains same as the original value
decreases to half the original value
tends to becomes zero
increases to two times the original value

⇒ A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because
synchronous motor has no slip
stator supply is not required to produce magnetic field
mechanical load on the rotor remains constant
synchronous motor has large airgap

⇒ The percentage slip in case of a synchronous motor is
0.01
1
0.005
zero

⇒ When load on an over-excited or underexcited synchronous motor is increased, rate of change of its armature current as compared with that of power factor is
more
less
equal
twice

⇒ The speed of the synchronous motor
increases with increase in load
decreases as load increases
varies with power factor
always remains constant

⇒ Slip-rings in a synchronous motor carry
direct current
alternating current
no current
all of the above

⇒ In a synchronous motor, the magnitude of stator back e.m.f. Eb depends on
load on the motor
d.c. excitation only
both the speed and rotor flux
none of the above

⇒ The angle between the rotor poles and stator poles, in a synchronous motor, is known as
power factor angle
torque angle
synchronizing angle
angle of retardation

⇒ The shaft of synchronous motor is made of
mild steel
chrome steel
alnico
stainless steel

⇒ The maximum speed variation in a 3- phase synchronous motor is
10 per cent
6 per cent
4 per cent
2 per cent

⇒ 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
increase in both armature current and power factor angle
increase in back e.m.f. but decrease in armature current
increase in both armature current and power factor which is lagging
increase in torque angle but decrease in back e.m.f.

⇒ In a synchronous motor it the back e.m.f. generated in the armature at noload is approximately equal to the applied voltage, then
the motor is said to be fully loaded
the torque generated is maximum
the excitation is said to be zero per cent
the excitation is said to be hundred per cent

⇒ Synchronous motors are generally not self-starting because
the direction of rotation is not fixed
the direction of instantaneous torque reverses after half cycle
startes cannot be used on these machines
starting winding is not provided on the machines

⇒ An important advantage of a synchronous motor over wound round induction motor is that
its power factor may be varied at will
its speed is independent of supply frequency
its speed may be controlled more easily
none of the above

⇒ Which of the following motors will be used in electric clocks ?
D.C. shunt motor
D.C. series motor
A.C. induction motor
A.C. synchronous motor