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

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

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Synchronous Motors
A synchronous motor connected to infinite bus-bars has at constant full load, 100% excitation and unity power factor. On changing the excitation only, the armature current will have

lagging power factor with over-excitation
leading power factor with under-excitation
leading power factor with over-excitation
no change of power factor

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