Synchronous machine, is used as motor/generator to supply active(KW) and reactive power(KVAR) used as power factor control(vector KVA=KW+KVAR) while in induction motor full load power factor, is almost constant around 0.8 lag and consumed only active power (KW)only to supply mechanical loading, though could be used as induction generator, if driven at super synchronous above Ns.
Historically, synchrounus motors were not only used for providing amechanical power at a constant speed, but they were also used as reactive power compensators for power factor improvement and voltage control. They can provide a fully controlled smooth inductive and capacitive power variations within their capability limits. These limits are defined based on many factors including the field winding rating, and the VA rating of the armature windings. Therefore, the rating of a synchrounus motor is usually defined in VA, but it can also be defined in W or hp, and power factor limits. On the other hand, usual induction motors are used for providing mechanical power under uncontrolled reactive power consumption. Therefore, they are usually rated by either W or hp.
Sync machines are able to change the p.f hence the VA. Induction motors consume constant VA power.
V curves of synchronous motor at different load would be the answer...
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