The principle of the synchronous motor is illustrated in Fig. 447.
In practice the synchronous motor has a number of pairs of field poles.
In a synchronous motor the armature reaches the 90 degree position at the exact instant at which the current reverses in the line.
This connects up the two armature coils in series, and the motor will then run as a synchronous motor.
A synchronous motor is one that keeps step with the alterations of an alternating current.