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Home⇒ Engineering⇒
Synchronous motors
1-Dont try to cram or spend more time here just read it fast and cover syllabus then practice MCQ's cheptor of same topic to check your progress. . |
2-Wrong options are also given but dont concentrate there, Right answer is in bold format. |
Q21 ⇒ 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 all of the above methods [other wrong options] [Discuss in forum] 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 |
Q22 ⇒ If the field circuit of an unloaded salientpole
synchronous motor gets suddenly
open-circuited, then the motor stops [other wrong options] [Discuss in forum] it runs at a slower speed it continues to run at the same speed it runs at a very high speed |
Q23 ⇒ In a synchronous motor, damper windings
are provided on pole faces [other wrong options] [Discuss in forum] stator frame rotor shaft none of the above |
Q24 ⇒ Hunting in a synchronous motor cannot
be due to windage friction [other wrong options] [Discuss in forum] variable load variable frequency variable supply voltage |
Q25 ⇒ 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 excitation is said to be hundred per cent [other wrong options] [Discuss in forum] the motor is said to be fully loaded the torque generated is maximum the excitation is said to be zero per cent |
Q26 ⇒ The duration of sudden snort-circuit
test on a synchronous motor is usually
about one second [other wrong options] [Discuss in forum] one hour one minute none of the above |
Q27 ⇒ 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 [other wrong options] [Discuss in forum] 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 none of the above |
Q28 ⇒ The angle between the rotor poles and
stator poles, in a synchronous motor, is
known as torque angle [other wrong options] [Discuss in forum] power factor angle synchronizing angle angle of retardation |
Q29 ⇒ A three-phase synchronous motor will
have two slip-rings [other wrong options] [Discuss in forum] no slip-rings one slip-ring three slip-rings |
Q30 ⇒ As the load is applied to a synchronous
motor, the motor takes more armature
current because the rotor by shifting its phase backward causes motor to take more current [other wrong options] [Discuss in forum] the increased load has 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 |
Q31 ⇒ 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
[other wrong options] [Discuss in forum]
|
Q32 ⇒ A synchronous motor will always stop
when excitation winding gets disconnected [other wrong options] [Discuss in forum] supply voltage fluctuates load in motor varies supply voltage frequency changes |
Q33 ⇒ The standard full-load power factor
ratings for synchronous motors are unity or 0.8 leading [other wrong options] [Discuss in forum] zero or 0.8 leading unity or 0.8 lagging unity or zero |
Q34 ⇒ The efficiency of a properly designed
synchronous motor will usually fall in
range 85 to 95% [other wrong options] [Discuss in forum] 60 to 70% 75 to 80% 99 to 99.5% |
Q35 ⇒ An important advantage of a synchronous
motor over wound round induction
motor is that its power factor may be varied at will [other wrong options] [Discuss in forum] its speed is independent of supply
frequency its speed may be controlled more easily none of the above |
Q36 ⇒ Armature of a synchronous machine is
kept fixed because all of the above reasons [other wrong options] [Discuss in forum] 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 |
Q37 ⇒ In which of the following motors the
stator and rotor fields rotate simultaneously
? Synchronous motor [other wrong options] [Discuss in forum] D.C. motor Reluctance motor Universal motor Induction motor |
Q38 ⇒ The induced e.m.f. in a synchronous
motor working on leading power factor
will be more than the supply voltage [other wrong options] [Discuss in forum] less than the supply voltage equal to the supply voltage |
Q39 ⇒ By which of the following methods the
constant speed of a synchronous motor
can be changed to new fixed value ? By changing the supply frequency [other wrong options] [Discuss in forum] By interchanging any two phases By changing the applied voltage By changing the load. |
Q40 ⇒ In a synchronous motor, the damping
winding is generally used to prevent hunting and provide the starting torque [other wrong options] [Discuss in forum] reduce the eddy currents provide starting torque only reduce noise level none of the above |
Or |