How does the synchronous condenser work under light loads?

Synchronous condenser:

• A synchronous motor takes a leading current when over-excited and, therefore, behaves as a capacitor
• An over-excited synchronous motor running on no load is known as synchronous condenser
• When such a machine is connected in parallel with the supply, it takes a leading current which partly neutralises the lagging reactive component of the load
• It works as a VAR generator.
• Thus, the power factor is improved

Advantages:

• By varying the field excitation, the magnitude of current drawn by the motor can be changed by any amount, this helps in achieving stepless control of power factor
• The motor windings have high thermal stability to short circuit currents
• The faults can be removed easily

Disadvantages:

• There are considerable losses in the motor
• The maintenance cost is high
• It produces noise
• Except in sizes above 500 kVA, the cost is greater than that of static capacitors of the same rating
• As a synchronous motor has no self-starting torque, therefore, an auxiliary equipment has to be provided for this purpose