Amortisseur Windings

Amortisseur windings are bars which are found in the rotor of synchronous motors.  These bars are short circuited similar to the rotor windings in a squirrel cage motor.  The function of these windings is to dampen the torsional oscillations in the rotor that may occur as a result of load fluctuations.  They are also known as damper windings.

The Amortisseur windings can also be used to start the synchronous motors.  The Synchronous motor is not self-starting.  Hence, motor starts initially as an induction motor through the action of the amortisseur windings.  When the sufficient speed has been attained, the excitation to the rotor of the synchronous machine is switched on.  The motor then runs at the synchronous speed as a synchronous machine. 

Amortisseur windings also play a role in preventing rotor overheating when a synchronous machine is exposed to negative sequence currents.  Negative sequence currents may be induced when a synchronous generator is subject to a short-circuit.  Under these conditions, a negative phase sequence currents is induced in the rotor of the generator.  The amortisseur winding provides a path for the rotor currents and prevents the from flowing through the rotor forging and cause overheating.

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