It can be said that among the main functions for the operation and control of the electric motors are starting, direction of rotation, stop, speed regulation, limiting of starting current, mechanical protection and electrical protection, among others. It should be noted that a machine only starts spinning at the instant when the load to be overcome, when it is at rest, is less than its starting torque. Alternating current motors, with the exception of universal motors, are constant speed machines. However, it is possible to re-connect the stator coils of an induction motor so that it doubles the number of poles.
Therefore, considering some cases of specific applications, there is a need for a rapid deceleration of the engine and the load. When the power supply line motor is switched off automatically, a device reverses rotation with the motor still in operation. Switching off the mains motor or stopping is done through a component, thus preventing it from starting in the opposite direction. In the case of synchronous motors one must rely on dynamic braking. Most of the motors, except single-phase motors, such as shaded pole and repulsion, can be used in both directions of rotation.