A three-phase asynchronous motor is a type of electric motor that is powered by simultaneously connecting to a three-phase AC power source (with a phase difference of 120 degrees). Due to the fact that the rotor and stator of a three-phase asynchronous motor rotate in the same direction but at different speeds, there is a slip rate, hence it is called a three-phase asynchronous motor.

Working principle: A three-phase asynchronous motor is an induction motor. After a current is applied to the stator, some of the magnetic flux passes through the short-circuit ring and generates induced current in it. The current in the short-circuit ring obstructs the change of magnetic flux, resulting in a phase difference between the magnetic flux generated by the short-circuit ring and the non short-circuit ring, thus forming a rotating magnetic field. After being powered on, the rotor winding induces electromotive force and current due to relative motion with the magnetic field. That is, the rotating magnetic field has a relative speed with the rotor and interacts with the magnetic field to generate electromagnetic torque, causing the rotor to rotate and achieve energy conversion.

Motor structure: I will focus on the main components, which are mainly composed of stator and rotor.

The stator is composed of stator core, stator winding, machine base, end cover, etc. The rotor consists of a shaft, a rotor iron core, and a rotor winding. According to the structure of the rotor winding, the rotor can be divided into wound rotor and squirrel cage rotor

1. Stator section:

Including the machine base, stator iron core, and stator winding. The machine base is usually made of cast iron or cast steel, and the iron core is made of silicon steel sheets stacked into a cylindrical shape. There are evenly distributed parallel slots on the inner circle of the iron core, and stator windings are installed in the slots. The stator winding is the circuit part of an electric motor, and the stator winding of a three-phase motor is composed of three-phase symmetrical windings. The three-phase windings of each phase are independent of each other and embedded in the stator at a mutual difference of 120 electrical angles. The starting and ending points of each winding are U1, U2, V1, V2, W1, W2, which are led out from the junction box on the machine base. According to the requirements, connect the three-phase stator windings into a star shape (Y-shape) or a triangle shape (A-shape). If the motor is connected in a star shape, the voltage borne by each phase winding of the motor is the phase voltage of the power supply. If it is connected in a triangle shape, the voltage borne by each phase winding of the motor is the line voltage of the power supply. Whether it is a star connection or a delta connection should consider the rated voltage of the motor. For example, if the rated voltage of the motor is 220V, a star connection should be used, and if the rated voltage is 380V, a delta connection should be used

2. Rotor section:

It is composed of rotor iron core, rotor winding, and shaft. The rotor core is also made of stacked silicon steel sheets and fixed on the shaft. There are also several evenly distributed parallel slots on the outer circumference of the rotor for placing the rotor winding. The rotor winding can be divided into two types based on its structure: squirrel cage type and winding type

(1) Squirrel cage rotor

A squirrel cage rotor is a type of rotor in which a bare conductor is inserted into each slot of the rotor core, and two short-circuit rings are used at each end of the core to connect the conductor into a whole, forming a self closed short-circuit winding. If the iron core is removed, the entire winding looks like a squirrel cage, so it is called a squirrel cage motor. The cage rotor of small and medium-sized motors is generally made of cast aluminum, while large motors use copper bars

(2) Wound rotor

A wound rotor is a type of motor in which symmetrical three-phase windings are embedded in parallel slots and connected in a star shape. Its ends are connected together, and its ends are respectively connected to three insulated slip rings on the rotating shaft. It is connected to the external circuit through electric brushes. This type of motor is called a wound motor