How the synchronous motor can be used as s synchronous condenser?

If a motor is spinning under no load, it is storing some energy in the rotating mass.
This energy can be stored and released in the same way capacitors and inductors store and release energy.
This is what a synchronous motor acting like a condenser is doing.
The way it appears to the power system is dependent upon the field current applied to it.
If used as a motor, this is controlled to keep it spinning at the desired speed under load.
If used as a condenser, it is controlled to determine whether it will be releasing power ahead of or behind the power system (absorbing or releasing VARs).

When a synchronous motor operates with a high leading power factor, we can connect it in parallel with some high inductive loads to rise the over-all power factor of the system and accordingly it acts as synchronous condenser.