Question is ⇒ An over-excited synchronous motor is used for, Options are ⇒ (A) fluctuating loads, (B) variable speed loads, (C) low torque loads, (D) power factor corrections, (E) , Leave your comments or Download question paper.

Question is ⇒ An over-excited synchronous motor is used for, Options are ⇒ (A) fluctuating loads, (B) variable speed loads, (C) low torque loads, (D) power factor corrections, (E) , Leave your comments or Download question paper. Previous question Next question


Q1.	An over-excited synchronous motor is used for
A.	fluctuating loads [Wrong Answer]
B.	variable speed loads [Wrong Answer]
C.	low torque loads [Wrong Answer]
D.	power factor corrections [Correct Answer]
View Answer 4 -2 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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⇒ 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

⇒ 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°)

⇒ 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

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

⇒ 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

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

⇒ The back e.m.f. in the stator of a synchronous motor depends on
number of poles
flux density
rotor speed
rotor excitation

⇒ A rotory converter can also be run as a
d.c. shunt motor
d.c. series motor
d.c. compound motor
induction motor

⇒ While starting a salient pole synchronous motor by induction motor action and connecting field discharge resistance across field, starting and accelerting torque is produced by
induction motor torque in field winding
induction motor torque in damper winding
eddy current and hysteresis' torque in pole faces
reluctance motor torque due to saliency of the rotor

⇒ 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

⇒ A synchronous motor develops maximum power when load angle is
45°
60°
90°
120°

⇒ 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 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

⇒ In a synchronous motor, V-curves represent relation between
armature current and field current
power factor and speed
field current and speed
field current and power factor

⇒ 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

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

⇒ 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

⇒ When V is the applied voltage, then the breakdown torque of a synchronous motor varies as
V
V^3/2
V²
1/V

⇒ In a synchronous motor running with fixed excitation, when the load is increased three times, its torque angle becomes approximately
one-third
twice
thrice
six times

⇒ If the field circuit of an unloaded salientpole synchronous motor gets suddenly open-circuited, then
it runs at a slower speed
the motor stops
it continues to run at the same speed
it runs at a very high speed

⇒ In which of the following motors the stator and rotor fields rotate simultaneously ?
D.C. motor
Reluctance motor
Universal motor
Synchronous motor

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

⇒ 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

⇒ As the load is applied to a synchronous motor, the motor takes more armature current because
the increased load has to take more current
the rotor by shifting its phase backward causes motor to take more current
the back e.m.f. decreases causing ah increase in motor current
the rotor strengthens the rotating field casuing more motor current

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

⇒ 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

⇒ 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 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%

⇒ Synchronsizing power of a synchronous machine is
direcly proportional to the synchronous reactance
inversely proportional to the synchronous reactance
equal to the synchronous reactance
none of the above

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