A synchronous motor is an AC electric motor in which, at steady state, the rotation of the shaft is synchronized with the frequency of the supply current; the rotation period is exactly equal to an integral number of AC cycles. Here are some key features of synchronous motors:
- They are capable of running at a constant speed irrespective of the load acting on them.
- They are machines with high efficiency.
- They are mainly used in high precision applications.
- The constant speed characteristic is achieved by interaction between a constant and rotating magnetic field.
- The rotor of a synchronous motor produces a constant magnetic field, and the stator produces a revolving magnetic field.
- The field coil of the stator is excited by a three-phase AC supply, which produces a revolving magnetic field that rotates at synchronous speed.
- The synchronous speed is the constant speed at which the motor generates the electromotive force.
Synchronous motors are used in different fields where high precision is necessary, such as in synchronous clocks, timers in appliances, tape recorders, and precision servomechanisms in which the motor must operate at a precise speed. They are also used in industrial sizes to provide an efficient means of converting AC energy to work, and they can operate at electrical efficiency above 95% for larger sizes.
