Use of AC motors in the industry

Types of AC motors

To generate a rotating field with AC motors and thus actuate the rotor, constructive measures are required in comparison to three-phase motors. Over time, different types of AC motors have been developed for the generation of the rotating field. These include:

• Single-phase asynchronous motor: A special type of three-phase asynchronous motors is the single-phase asynchronous motor. Like any asynchronous machine, this AC motor also has a squirrel-cage rotor. The major disadvantage of the first motors of this type was that they could not start automatically. In the early to mid-twentieth century, when used in agricultural machinery, the rotor was thus actuated by hand or other means. Today, the single-phase asynchronous motor is often equipped with an auxiliary winding and a series-connected operating capacitor (capacitor motor). Together with the parallel-connected main winding, they generate the rotating field. Apart from the operating capacitor, you can optionally connect a starting capacitor, which provides a high starting torque. A mechanical or electronic switch will switch off this starting capacitor (as its name suggests) after the start-up. Major advantages of single-phase asynchronous motors are their minimum noise emissions, freedom from maintenance, and their robust and economic design.
• Single-phase series motor:
  The single-phase series motor can be operated with both direct and alternating current, and is therefore often called “universal motor”. A current reverser (commutator) generates its rotary movement. It is often used to drive tools (for example drilling machines) and household appliances (vacuum cleaners, etc.) as it provides high speeds and a high starting torque while being very space-saving.