Join 60,000+ competitive exam aspirants
or with email
Your Cart
SubtotalтВ╣0
TotalтВ╣0
Examoogle тАв User тАв info@examoogle.com тАв EE-2024-8821
Chapter 1 of 12 тАв Page 1 of 248ЁЯФТ Protected PDF тАв Watermarked
Join 60,000+ competitive exam aspirants
Synchronous motor always runs at
Syn. speed
Less than syn. speed
More than syn. speed
None of above
Syn. speed
A synchronous motor is defined by its rotor speed being strictly tied to the frequency of the supply current. It operates at exactly the synchronous speed (NsтАЛ), as the magnetic poles of the rotor lock into the rotating magnetic field produced by the stator.
A synchronous motor is defined by its rotor speed being strictly tied to the frequency of the supply current. It operates at exactly the synchronous speed (NsтАЛ), as the magnetic poles of the rotor lock into the rotating magnetic field produced by the stator.
NsтАЛ=P120fтАЛ тАФ where NsтАЛ is synchronous speed in rpm, f is supply frequency, and P is the number of poles.
The synchronous motor operates based on the principle of magnetic locking between the stator's rotating magnetic field and the rotor's DC-excited magnetic poles. Because the rotor is locked to the stator flux speed, the motor maintains a constant average speed regardless of load variations, provided the load does not exceed the pull-out torque limit.
The rotor speed is constant and independent of the load up to the pull-out torque.
Synchronous motors are not self-starting; they require an auxiliary mechanism or damper windings to reach synchronous speed.
The motor can be operated at leading, lagging, or unity power factor by adjusting the rotor excitation.
If the load exceeds the pull-out torque, the motor loses synchronism and stops (stalls).
Constant speed operation regardless of load
Ability to improve power factor by adjusting excitation
Not self-starting; requires additional equipment
More complex construction due to DC excitation requirement
Industrial drives requiring constant speed
Power factor correction (Synchronous Condensers)
The synchronous speed is fixed by the supply frequency and the physical pole count of the machine.
Option B (Less than synchronous speed) describes the behavior of an Induction Motor, which requires slip to produce torque.
Option C (More than synchronous speed) describes a synchronous generator (alternator) operating as a prime mover or braking mode, not as a standard motor.
A is correct тАФ A synchronous motor rotates at the synchronous speed (NsтАЛ) because the rotor poles magnetically lock with the rotating stator flux.
Always remember that in an induction motor, slip s>0, whereas in a synchronous motor, the slip is always exactly zero (s=0) during steady-state operation.