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Synchronous motor can be started by
Pony motor
DC motor
Damper winding
All of above
All of above
A synchronous motor is not self-starting because the stator magnetic field rotates at synchronous speed, while the rotor is massive and cannot instantly accelerate to catch up. External methods are required to bring the rotor close to synchronous speed so that magnetic locking can occur.
A synchronous motor is not self-starting because the stator magnetic field rotates at synchronous speed, while the rotor is massive and cannot instantly accelerate to catch up. External methods are required to bring the rotor close to synchronous speed so that magnetic locking can occur.
NsтАЛ=P120fтАЛ тАФ Synchronous speed formula where P is poles and f is frequency.
TstartтАЛ=Induction┬аTorque+Reluctance┬аTorque тАФ Total starting torque mechanism.
The most common method is the use of damper windings, which act like an induction motor's squirrel-cage rotor to generate torque at standstill. Alternatively, a Pony motor (a small induction motor) or a DC machine coupled to the shaft can accelerate the rotor to synchronous speed, at which point the machine is synchronized to the supply.
Synchronous motors have zero starting torque without additional measures.
Damper windings are embedded in the pole faces of the rotor.
Synchronization occurs when the DC excitation is applied once the speed is тЙИ95тИТ97% of NsтАЛ.
Once synchronized, the motor runs at a constant synchronous speed regardless of load variations (within stability limits).
Damper windings are cheap and integrated into the motor.
External motors allow for precise control during the starting sequence.
Auxiliary motors increase the physical size and maintenance requirements.
Starting under heavy load requires complex clutches or soft-starting equipment.
Power factor correction (Synchronous Condensers).
Industrial drives requiring constant speed like centrifugal pumps and compressors.
Pony motor is an auxiliary motor that must be capable of bringing the main motor to the rated speed.
DC motor starting is typically used in motor-generator sets where the DC machine is available on the same shaft.
Damper windings also serve to damp out oscillations (hunting) during transient load changes.
D is correct тАФ All listed methods provide the necessary initial acceleration to reach speeds where the rotor can lock into the rotating magnetic field of the stator.
Always remember that a standard synchronous motor acts like an induction motor during the starting phase when damper windings are used, but switches to synchronous mode once excited.