A synchronous motor develops maximum power when load angle is
45°
60°
90°
120°
Q.2.
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 m.f. will be more than the supply voltage
Q.3.
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
Q.4.
The construction of a synchronous motor resembles
a series motor
an induction motor
an alternator
a rotary converter
Q.5.
A synchronous machine with low value of short-circuit ratio has
lower stability limit
high stability limit
good speed regulation
good voltage regulation
Q.6.
The duration of sudden snort-circuit test on a synchronous motor is usually about
one hour
one minute
one second
none of the above
Q.7.
The size of a synchronous motor decreases with the increase in
flux density
horse power rating
speed
all of the above
Q.8.
The back e.m.f. in the stator of a synchronous motor depends on
number of poles
flux density
rotor speed
rotor excitation
Q.9.
If the field of a synchronous motor is underexcited, the power factor will be
zero
unity
lagging
leading
Q.10.
In a synchronous motor it the back e.m.f. generated in the armature at noload isapproximately 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
Q.11.
A synchronous motor connected to infinite bus-bars has at constant full load,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 under-excitation
leading power factor with over-excitation
Q.12.
By which of the following methods the constant speed of a synchronous motor can bechanged to new fixed value ?
By changing the supply frequency
By interchanging any two phases
By changing the applied voltage
By changing the loa
Q.13.
Hunting in a synchronous motor cannot be due to
windage friction
variable load
variable frequency
variable supply voltage
Q.14.
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
Q.15.
The ratio of starting torque to running torque in a synchronous motor is
zero
one
two
infinity
Q.16.
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 Eh and V
Q.17.
The induced e.m.f. in a synchronous motor working on leading power factor will be
more than the supply voltage
less than the supply voltage
equal to the supply voltage
none
Q.18.
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
Q.19.
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
Q.20.
The maximum speed variation in a 3-phase synchronous motor is
10 per cent
6 per cent
4 per cent
zero
Q.21.
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
Q.22.
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
Q.23.
The power factor of a synchronous motor is better than that of induction motor because
stator supply is relieved of responsibility of producing magnetic field
mechanical load on the motor can be adjusted
synchronous motor runs at synchronous speed
synchronous motor has large air gap
Q.24.
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
all of the above methods
Q.25.
Change of D.C. excitation of a synchronous motor changes
applied voltage of the motor
motor speed
power factor of power drawn by the motor
any of the above
Q.26.
An important advantage of a synchronous motor over wound round induction motoris 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
Q.27.
A synchronous machine with large air gap has
a higher value of stability limit
a small value of inherent regulation
a higher synchronizing power which makes the machine less sensitive to load variations
all of the above
Q.28.
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
Q.29.
A synchronous motor can be made self starting by providing
damper winding on rotor poles
damper winding on stator
damper winding on stator as well as rotor poles
none of the above
Q.30.
The shaft of synchronous motor is made of
mild steel
chrome steel
alnico
stainless steel
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