When Synchronous Motor operates at leading power factor then Rotor is overexcited in such a way that back emf (which is generated in Stator due to DC excitation of the Rotor) is greater then the supply voltage (V). In this case, a Synchronous Motor will be operating at leading Power factor. At this time Resultant flux is greater that that is required for unity Power factor, then this flux will generate Reactive Power so the motor will generate Reactive Power. And it will use Active Power too for Mechanical work. Therefore synchronous motor working on leading PF will work as a synchronous condenser.