Question is ⇒ A synchronous motor develops maximum power when load angle is, Options are ⇒ (A) 45°, (B) 60°, (C) 90°, (D) 120°, (E) , Leave your comments or Download question paper.

Question is ⇒ A synchronous motor develops maximum power when load angle is, Options are ⇒ (A) 45°, (B) 60°, (C) 90°, (D) 120°, (E) , Leave your comments or Download question paper. Previous question Next question


Q1.	A synchronous motor develops maximum power when load angle is
A.	45° [Wrong Answer]
B.	60° [Wrong Answer]
C.	90° [Correct Answer]
D.	120° [Wrong Answer]
View Answer 5 -4 Explanation:- Answer : C 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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⇒ 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 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

⇒ 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

⇒ The working of a synchronous motor is similar to
gear train arrangement
transmission of mechancial power by shaft
distribution transformer
turbine

⇒ The angle between the rotating stator flux and rotor poles is called____ angle
torque
obtuse
synchronizing
power factor

⇒ 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

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

⇒ For V-curves for a synchronous motor the graph is drawn between
field current and armature current
terminal voltage and load factor
power factor and field current
armature current and power factor

⇒ An over-excited synchronous motor takes
leading current
lagging current
both (a) and (b)
none of the above

⇒ 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

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

⇒ 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

⇒ Armature of a synchronous machine is kept fixed because
of reducing number of slip rings on the rotor
armature is associated with large power as compared to the field circuits
of difficulty of providing high voltage insulation on rotor
all of the above reasons

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

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

⇒ 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

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

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

⇒ 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

⇒ Under which of the following conditions hunting of synchronous motor is likely to occur ?
Periodic variation of load
Over-excitation
Over-loading for long periods
Small and constant load

⇒ 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

⇒ 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

⇒ 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

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

⇒ 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

⇒ 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

⇒ Synchronous motors are generally not self-starting because
the direction of rotation is not fixed
the direction of instantaneous torque reverses after half cycle
startes cannot be used on these machines
starting winding is not provided on the machines

⇒ 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 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°)