Basic structure of three-phase asynchronous motor

A three-phase asynchronous motor mainly consists of a stator and a rotor, with the stator being the stationary part and the rotor being the rotating part. There is a certain air gap between the stator and rotor. The stator winding is a symmetrical three-phase winding that generates a rotating magnetic field.

It is based on the principles of electromagnetic induction and electromagnetic force. The interaction between stator rotating magnetic field (synthetic magnetic field) and rotor current.

1. Stator

The stator consists of an iron core, windings, and a machine base.

The stator core is a part of the magnetic circuit, which is fixed as a whole on the machine base by stacking 0.5mm thick silicon steel sheets. The sheets are insulated from each other to reduce eddy current consumption. The inner circle of the stator core is punched with stator slots, in which coils are placed.

The stator winding is the circuit part of an electric motor, which is divided into three symmetrical parts distributed on the stator core, called the three-phase winding. The three-phase winding is connected to a three-phase AC power supply, and the current in the three-phase winding generates a rotating magnetic field in the stator core.

The machine base is mainly used to fix and support the stator core.

2. Rotor

The rotor is composed of an iron core and windings.

The rotor core is also a part of the magnetic circuit of the electric motor, which is assembled as a whole on the shaft by stacking silicon steel sheets. The inner circle of the rotor core is punched with rotor slots, in which coils are placed.

The function of the rotor is to generate rotor current, that is, to generate electromagnetic torque. The rotor has squirrel cage and winding types. Due to its various advantages, squirrel cage asynchronous motors are widely used.

The winding is composed of coils, and the three-phase winding is symmetrically placed in the iron core slot. The rotor winding is connected to an external resistor in the rotor circuit through slip rings and brushes on the shaft to improve starting performance and regulate speed.

When the symmetrical three-phase winding of the stator is connected to a three-phase power supply, a symmetrical three-phase current will pass through the winding and generate a magnetic field in space, which rotates along the circumference of the stator. When the magnetic field rotates, the cutting magnetic flux of the rotor winding conductor will generate induced electromotive force. Due to the presence of electromotive force, rotor current will be generated in the rotor winding. According to Ampere's law of electromagnetic mechanics, the interaction between rotor current and rotating magnetic field will generate electromagnetic force, which forms electromagnetic torque on the axis of the rotor. The direction of torque action is the same as the direction of rotation of the rotating magnetic field. The rotor will rotate according to the optional direction of the rotating magnetic field under the action of this torque.

The origin of asynchronous motors. The rotor speed is different from the synchronous speed, and the speed difference between the rotor and the rotating magnetic field is the main factor ensuring the rotation of the rotor. The value range of S is 0-1. It is also a very important physical quantity.