Question is ⇒ In a synchronous motor, V-curves represent relation between, Options are ⇒ (A) armature current and field current, (B) power factor and speed, (C) field current and speed, (D) field current and power factor, (E) , Leave your comments or Download question paper.

Question is ⇒ In a synchronous motor, V-curves represent relation between, Options are ⇒ (A) armature current and field current, (B) power factor and speed, (C) field current and speed, (D) field current and power factor, (E) , Leave your comments or Download question paper. Previous question Next question


Q1.	In a synchronous motor, V-curves represent relation between
A.	armature current and field current [Correct Answer]
B.	power factor and speed [Wrong Answer]
C.	field current and speed [Wrong Answer]
D.	field current and power factor [Wrong Answer]
View Answer 6 -3 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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⇒ 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

⇒ 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

⇒ 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

⇒ When V is the supply voltage and R is the rotor resistance per phase, the mechanical power developed by the synchronous motor will be proportional to

V²

R²

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

⇒ 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

⇒ Power factor of a synchronous motor is unity when
the armature current is maximum
the armature current is minimum
the armature current is zero
none of the above

⇒ In a synchronous machine in case the axis of field flux is in line with the armature flux, then
the machine is working as synchronous generator
the machine is working as synchronous motor
the machine will vibrate violently
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 shaft of synchronous motor is made of
mild steel
chrome steel
alnico
stainless steel

⇒ Dust and dirt accumulation on motor winding will result in
rise in winding temperature
increased core losses
shorting of coils
eddy current flow

⇒ The mechanical displacement of the rotor with respect to the stator, in polyphase multipolar synchronous motor running at full load, is of the order of
zero degree
two degrees
five degrees
ten degrees

⇒ In a synchronous motor, the armature current has large values for
high excitation only
low excitation only
both high and low excitation
none of the above

⇒ If one-phase of a 3-phase synchronous motor is short-circuited, motor
will refuse to start
will overheat in spots
will not come upto speed
will fail to pull into step

⇒ Synchronous motor always runs at
the synchronous speed
less than synchronous speed
more than synchronous speed
none of the above

⇒ 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 rotor copper losses, in a synchronous motor, are met by
d.c. source
armature input
motor input
supply lines

⇒ In case one phase of a three-phase synchronous motor is short-circuited the motor will
not start
run at 2/3 of synchronous speed
run with excessive vibrations
take less than the rated load

⇒ The magnitude of field flux in a 3-phase synchronous motor
remains constant at all loads
varies with speed
varies with the load
varies with power factor

⇒ The effect of increasing the load on a synchronous motor running with normal excitation is to
decrease both arrnature current and power factor
decrease armature current but increase power factor
increase armature current but decrease power factor
increase both its armature current and power factor

⇒ The minimum armature current of the synchronous motor corresponds to operation at
zero power factor leading
unity power factor
0.707 power factor lagging
0.707 power factor leading

⇒ In a synchronous motor, damper windings are provided on
stator frame
rotor shaft
pole faces
none of the above

⇒ When the field of a synchronous motor is under-excited, the power factor will be
leading
lagging
unity
zero

⇒ For power factor correction, synchronous motors operate at
no-load and greatly over-excited fields
no-load and under-excited fields
normal load with minimum excitation
normal load with zero excitation

⇒ The oscillations in a synchronous motor can be damped out by
maintaining constant excitation
running the motor on leading power factors
providing damper bars in the rotor pole faces
oscillations cannot be damped

⇒ 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

⇒ 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

⇒ At no-load, the armature current in a synchronous motor
is zero
lags the applied voltage by 900
leads the applied voltage by 90°
is in phase with the applied voltage

⇒ A synchronous motor can operate at
lagging power factor only
leading power factor only
unity power factor only
lagging, leading and unity power factors

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