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Slip of synchronous motor is always
The slip of a synchronous motor is always zero. This is because, by definition, the rotor of a synchronous motor rotates at exactly the same speed as the rotating magnetic field produced by the stator, known as the synchronous speed (NsтАЛ).
The slip of a synchronous motor is always zero. This is because, by definition, the rotor of a synchronous motor rotates at exactly the same speed as the rotating magnetic field produced by the stator, known as the synchronous speed (NsтАЛ).
NsтАЛ=P120fтАЛ тАФ Synchronous speed formula
s=NsтАЛNsтАЛтИТNrтАЛтАЛ тАФ Slip calculation formula
s=0 тАФ Characteristic condition for synchronous motors
In a synchronous motor, the stator is supplied with an AC supply that creates a rotating magnetic field revolving at NsтАЛ=P120fтАЛ. The rotor is excited by a DC supply, creating fixed magnetic poles. These poles lock into the rotating magnetic field, forcing the rotor to revolve at NsтАЛ regardless of the load (up to the pull-out torque). Since the motor speed (NrтАЛ) equals the synchronous speed (NsтАЛ), the slip s=NsтАЛNsтАЛтИТNrтАЛтАЛ becomes zero.
Synchronous machines maintain constant speed regardless of load variations, provided stability is maintained.
Slip is a fundamental parameter only in asynchronous (induction) machines.
The rotor poles 'lock' with the stator flux poles through magnetic coupling.
Constant speed operation
Ability to operate at leading power factor for power factor correction
Not self-starting (requires damper windings or pony motors)
Requires separate DC excitation for the rotor
Power factor correction
Large industrial drives
Constant speed applications
In induction motors, slip is never zero; it typically ranges from 2% to 5% at full load.
If a synchronous motor pulls out of synchronism, it loses its synchronous characteristic and usually stalls or hunts, behaving as an unstable system.
A is correct тАФ The slip of a synchronous motor is always zero as the rotor speed is perfectly synchronized with the stator flux speed.
Always remember: 'Synchronous' implies matching frequency/speed, meaning the relative velocity between rotor and stator flux is zero, hence slip is zero.