Synchronous Motors
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

eddy current and hysteresis torque in pole faces
induction motor torque in field winding
induction motor torque in damper winding
All of the listed here

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Synchronous Motors
The power factor of a synchronous motor is better than that of induction motor because

synchronous motor runs at synchronous speed
mechanical load on the motor can be adjusted
stator supply is relieved of responsibility of producing magnetic field
synchronous motor has large air gap

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