Synchronous Motors
An important advantage of a synchronous motor over wound round induction motor is that

None of these
its speed is independent of supply frequency
its speed may be controlled more easily
its power factor may be varied at will

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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

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

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