Synchronous motors and induction motors are the most widely used types of AC motors used in industry. With a synchronous electric motor running at a steady state, the rotation of the rotor is synchronized with the frequency of the supply current. Synchronous motors are available in a wide range of sizes, from sub-fractional self-excited to large high-horsepower industrial sizes, rated up to 15 mW and speeds ranging from 150 to 1800 rev/min.