Sorry to take so long for a reply, but here's a bit 'O information regarding Synchronous Motors used as Synchronous Condensers.
Hope it's helpful and useful - let me know if you have additional Questions.
Synchronous Motors have been used on account of their ability to raise the Power Factor of Systems having large Induction Motor loads, since the Power factor of such systems is frequently quite low.
In many cases, however, they may cost less and have higher efficiencies than the corresponding induction motor. This is especially true for low speed motors.
Many Synchronous Motors are designed to run at Unity Power Factor; i.e., sufficient excitation is supplied to meet the requirements of the motor only, and no reactive current is either drawn from or supplied to the power system.
In the case when it is desirable to have the Synch. Motor furnish a part of the reactive current required by the system (to bring it into / close to unity power factor), the motor is designed to operate at 80% LEADING Power Factor, and draw currents which LEADS the Voltage rather than Lags the Voltage - as is the case with Induction Motors and Transformers.
For this, the Synch. Motor gets greater excitation than that necessary for unity power factor.
The power factor correction is accomplished by resolving all currents into energy and reactive components, and taking the algebraic sums of each separately, or by means of a vector diagram.
It's been a long time for me, and the old "Database" in my head is very dusty!, so let me do some research and make an additional reply later.
If I forget to do so by Saturday Evening, send me a threatening reply and/or E-mail!
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