An AC electric motor is named for the type of power that it uses, specifically alternating current electricity.
Consisting primarily of a stator and rotor there are two different types of AC motors; induction motors and synchronous motors. Each of these two types uses the same basic principle: the stator’s coils of wires create a magnetic field that moves in the direction of the AC current flow. The rotor can be thought of like the water wheel being spun by a flowing river, only in this case the rotor is being spun by the change in magnetic force.
The difference between the induction motor and a synchronous motor is that the synchronous motor doesn’t use induced current. The Synchronous motor uses a magnetic field generated by the current passing through a permanent magnet or a slip ring and, because of this, the synchronous motor is more precise and operates at a faster speed.
Variable frequency drives are often paired with AC motors in order to moderate motor speeds and conserve energy consumption. Since AC motors operate at specific fixed speeds, and the application usually calls for a slower speed, the variable frequency drive is used to both create efficiencies as well as generate the correct RPM (Rotations per minute) required by the device needing driven. Often the power savings will pay for the cost of the variable frequency drive.
In addition, the variable frequency drive can slow the acceleration or deceleration as well as adjust when the AC motor actually runs. Fine tuning these settings can reduce the wear and tear on the motor, extending the useful life and getting further bang for the buck. For most applications like fans, pumps and similar, an immediate full speed start is not required and a gradual acceleration and deceleration is fine. Obviously if the motor doesn’t need to be running, then the life-span of the motor increases. Variable frequency drives, then, have a multitude of uses and are a function addition to most AC motors.
The AC motor has come a long way since the first prototype built by Hippolyte Pixii in 1832, which was only a horseshoe magnet passing over two wound wire coils. Still, the fundamentals have not changed and the application of AC power being able to power devices remains a constant.