Question is ⇒ 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, Options are ⇒ (A) will become more, (B) will become less, (C) will remain unchanged, (D) none of the above, (E) , Leave your comments or Download question paper.

Question is ⇒ 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, Options are ⇒ (A) will become more, (B) will become less, (C) will remain unchanged, (D) none of the above, (E) , Leave your comments or Download question paper. Previous question Next question


Q1.	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
A.	will become more [Wrong Answer]
B.	will become less [Correct Answer]
C.	will remain unchanged [Wrong Answer]
D.	none of the above [Wrong Answer]
View Answer 9 -14 Explanation:- Answer : B 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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⇒ Which of the following losses, in a synchronous motor, does not vary with load ?
Windage loss
Copper losses
Any of the above
None of the above

⇒ The armature current of the synchronous motor
has large values for low excitation only
has large values for high excitation only
has large values for low and high excitation
any of the above

⇒ A synchronous motor is running with normal excitation. When the load is increased, the armature current drawn by it increases because
speed of the motor is reduced
power factor is decreased
Eb (back e.m.f.) becomes less than V (applied voltage)
Er (net resultant voltage) in armature is increased

⇒ 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
reluctance torque

⇒ 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

⇒ 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

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

⇒ Higher the applied ____voltage will be the stator flux and____ will be the pullin torque
lower, lower
lower, greater
greater, lower
greater, greater

⇒ The standard full-load power factor ratings for synchronous motors are
zero or 0.8 leading
unity or 0.8 lagging
unity or 0.8 leading
unity or zero

⇒ In a synchronous motor, the damping winding is generally used to
prevent hunting and provide the starting torque
reduce the eddy currents
provide starting torque only
reduce noise level

⇒ The speed of a synchronous motor
increases as the load increases
decreases as the load decreases
always remains constant
none 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
d.c. motor toque

⇒ A synchronous machine with low value of short-circuit ratio has
lower stability limit
high stability limit
good speed regulation
good voltage regulation

⇒ A synchronous motor connected to infinite bus-bars has at constant full load, 100% excitation and unity power factor. On changing the excitation only, the armature current will have
no change of power factor
lagging power factor with over-excitation
leading power factor with underexcitiltion
leading power factor vvith over-excitation

⇒ 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
Low field current

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

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

⇒ A synchronous motor can be used as a synchronous capacitor when it is
under-loaded
over-loaded
under-excited
over-excited

⇒ If the synchronous motor, properly synchronised to the supply is running on no load and is having negligible loss then
the stator current will be zero
the stator current will be very small
the stator current will be very high
the back e.m.f. will be more than the supply voltage

⇒ 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

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

⇒ A synchronous motor can develop synchronous torque
when under loaded
while over-excited
only at synchronous speed
below or above synchronous speed

⇒ A synchronous motor running with normal excitation adjusts to load increases essentially by increase in
back e.m.f.
armature current
power factor
torque angle

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

⇒ The maximum power developed in a synchronous motor will depend on
the rotor excitation only
the supply voltage only
the rotor excitation and supply voltage both
the rotor excitation, supply voltage and maximum value of coupling angle (90°)

⇒ 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

⇒ A pony motor is basically a
small induction motor
D.C. series motor
D.C. shunt motor
double winding A.C./D.C. motor

⇒ In a 3-phase, 4-pole, 50 Hz synchronous motor, the frequency, pole number and load torque all are halved. The motor speed will be
3000 r.p.m.
1500 r.p.m.
750 r.p.m.
none of the above

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

⇒ 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