Three basic approaches can be used to safely start a synchronous motor:
1.Reduce the speed of the stator magnetic field to a low enough value that
the rotor can accelerate and two magnetic fields lock in during one halfcycle
of field rotation. This can be achieved by reducing the frequency of
the applied electric power (which used to be difficult but can be done
now).
2.Use an external prime mover to accelerate the synchronous motor up to
synchronous speed, go through the paralleling procedure, and bring the
machine on the line as a generator. Next, turning off the prime mover will
make the synchronous machine a motor.
3.Use damper windings or amortisseur windings – the most popular