Question is ⇒ For power factor correction, synchronous motors operate at, Options are ⇒ (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 excitation, (E) , Leave your comments or Download question paper.

Question is ⇒ For power factor correction, synchronous motors operate at, Options are ⇒ (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 excitation, (E) , Leave your comments or Download question paper. Previous question Next question


Q1.	For power factor correction, synchronous motors operate at
A.	no-load and greatly over-excited fields [Correct Answer]
B.	no-load and under-excited fields [Wrong Answer]
C.	normal load with minimum excitation [Wrong Answer]
D.	normal load with zero excitation [Wrong Answer]
View Answer 5 -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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⇒ 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

⇒ In a synchronous motor, the maximum power developed depends on all of the following except
rotor excitation
maximum value of coupling angle
direction of rotation
supply voltage

⇒ An over-excited synchronous motor is used for
fluctuating loads
variable speed loads
low torque loads
power factor corrections

⇒ A three-phase synchronous motor will have
no slip-rings
one slip-ring
two slip-rings
three slip-rings

⇒ 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

⇒ Hunting in a synchronous motor cannot be due to
windage friction
variable load
variable frequency
variable 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

⇒ A synchronous motor can be made selfstarting by providing
damper winding on rotor poles
damper winding on stator
damper winding on stator as well as rotor poles
none of the above

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

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

⇒ 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 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

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

⇒ The duration of sudden snort-circuit test on a synchronous motor is usually about
one hour
one minute
one second
none of the above

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

⇒ The maximum value of torque that a synchronous motor can develop without losing its synchronism is known as
slip torque
pull-out torque
breaking torque
synchronising torque

⇒ The size of a synchronous motor decreases with the increase in
flux density
horse power rating
speed
all of the above

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

⇒ If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will
stop
run as induction motor
function as static condenser
burn with dense smoke

⇒ Exciters of synchronous machines are
d.c. shunt machines
d.c. series machines
d.c. compound machines
any 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

⇒ In a 3-phase synchronous motor, the negative phase sequence exists when the motor is
supplied with unbalanced voltage
under-loaded
over-loaded
none of the above

⇒ In a synchronous motor, the magnitude of stator back e.m.f. Eb depends on
d.c. excitation only
speed of the motor
load on the motor
both the speed and rotor flux

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

⇒ Synchronous motors are
not-self starting
self-starting
essentially self-starting
none of the above

⇒ 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

⇒ When a 3-phase synchionous generator is supplying a zero power factor lagging load, the armature field affects the main field in the following way
augments it directly
directly opposes it
cross-magnetises it
none of the above

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

⇒ A synchronous motor can be started by
pony motor
D.C. compound motor
providing damper winding
any 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