A synchronous motor working on leading power factor
and not driving any mechanical is known as:
(1) Synchronous induction motor (2) Spinning motor
(3) Synchronous condenser (4) None of these
Answers
When ever a synchronous machine( either motor or generator) is being operated at leading power factor(PF), it always shed out its leading Reactive VARs( volta-ampere reactives) for such machine which is defficient with leading VARs( operating at lagging PF) and thus the VARs defficient machine will absorb that leading VARs supplied and tend to improve its lagging PF to unity./
Now, when this machine is done with improvement of its PF from lagging to unity and still being fed with Leading VARs in excess, it will eventually start acting like a source of Leading VARs for some other Leading VARs defficient machines connected in the power system.
Synchronous condensers( phase modifiers) are the best examples for this kind of practises. Phase modifier is nothing but an un loaded synchronous motor operated at leading PF and without load.
By this practise, the power factor is improved and the overall performance of the entire power system gets improved.
Further, to answer this question, since the question is about the synchronous motor, always remember that any kind of motor (either synchronous or induction or DC)require active power to do the mechanical work. Now, if it is being perated at leading PF(only in case of AC motors, as described above) it will supply the reactive power (+Q) and if it is operating at lagging PF, it will absorb the reactive power(-Q), where symbols have their usual meanings .