Basic structure of three-phase AC asynchronous motor

A three-phase AC asynchronous motor is an electric drive device that converts electrical energy into mechanical energy. It mainly consists of the stator, rotor, and the air gap between them. After the stator winding is connected to the three-phase AC power supply, a rotating magnetic field is generated and the rotor is cut to obtain torque. The three-phase AC asynchronous motor has the advantages of simple structure, reliable operation, low price, strong overload capacity, and convenient use, installation, and maintenance. It is widely used in various fields. Today, we will talk about its basic structure.

The three-phase asynchronous motor is mainly composed of the stator (fixed part), rotor (rotating part), bearings, etc. The stator is mainly composed of the stator core, three-phase winding, frame, and end cover. The rotor mainly consists of a shaft, rotor core, and rotor winding.

Stator core: Generally made of 0.35-0.5mm thick silicon steel sheets with an insulation layer on the surface, punched and laminated, with evenly distributed slots punched in the inner circle of the core for embedding the stator winding.

Three-phase winding: It is composed of three identical windings arranged at an electrical angle of 120 ° apart in space, with each coil embedded in each slot of the stator according to a certain pattern. Its function is to connect three-phase alternating current and generate rotating magnetic field.

Frame: Usually made of cast iron, the frame of large asynchronous motors is usually welded with steel plates, while the frame of micro motors is made of cast aluminum. Its function is to fix the stator core and front and rear end covers to support the rotor, and to provide protection, heat dissipation, and other functions.

End cover: mainly used to fix the rotor, support and protect it.

Rotor core: The material used is the same as the stator, made of 0.5mm thick silicon steel sheets punched and laminated, with evenly distributed holes punched on the outer circle of the silicon steel sheets to accommodate the rotor winding. Usually, the stator core is used to punch the inner circle of the lagging silicon steel sheet to make the rotor core. Generally, the rotor core of small asynchronous motors is directly pressed onto the shaft, while the rotor core of large and medium-sized asynchronous motors (with a rotor diameter of over 300-400 millimeters) is pressed onto the shaft with the help of a rotor bracket.

Rotor winding:

a) Squirrel cage rotor: The rotor winding is composed of multiple guide bars inserted into the rotor slot and two circular end rings. If the rotor core is removed, the entire winding will look like a squirrel cage, hence it is called a cage winding. Small cage motors use cast aluminum rotor windings, and for motors above 100KW, they are welded with copper bars and copper end rings. The squirrel cage rotor is divided into several types: impedance rotor, single squirrel cage rotor, double squirrel cage rotor, and deep groove rotor, with different starting torque and other characteristics.

b) Wound rotor: The wound rotor winding is similar to the stator winding and is also a symmetrical three-phase winding. It is generally connected in a star shape, and the three outlet heads are connected to the three collector rings of the shaft, and then connected to the external circuit through an electric brush.