Synchronous Motors.

•When a short-circuit occurs upstream of a synchronous motor, the system voltage goes to zero, and the motor begins losing speed. As the motor slows down, the inertia of the load is actually turning the motor and causing it to act like a generator. The synchronous motor has a dc field winding, like a generator, and actually delivers short-circuit current into the fault until the motor completely stops. As with a generator, the short-circuit current is limited only by the synchronous motor impedance and the circuit impedance between the motor and the fault.