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The working principle of three-phase asynchronous motor

Updated:03-08-2021
Summary:

Three-phase asynchronous motor (Triple-phase asynchrono […]

Three-phase asynchronous motor (Triple-phase asynchronous motor) is a type of induction motor. It is a type of motor powered by 380V three-phase alternating current (phase difference 120 degrees) at the same time. Because the rotor and stator of the three-phase asynchronous motor rotate The magnetic field rotates in the same direction and at different speeds, and there is a slip rate, so it is called a three-phase asynchronous motor. The speed of the rotor of the three-phase asynchronous motor is lower than the speed of the rotating magnetic field. The rotor winding generates electromotive force and current due to the relative movement between the magnetic field and the magnetic field, and interacts with the magnetic field to generate electromagnetic torque to realize energy conversion.

Compared with single-phase asynchronous motors, three-phase asynchronous motors have better running performance and can save various materials. According to different rotor structures, three-phase asynchronous motors can be divided into two types: cage type and winding type. The cage rotor asynchronous motor has simple structure, reliable operation, light weight and low price, and has been widely used. Its main disadvantage is the difficulty of speed regulation. The rotor and stator of the wound three-phase asynchronous motor are also provided with three-phase windings and connected to an external varistor through slip rings and brushes. Adjusting the resistance of the rheostat can improve the starting performance of the motor and adjust the speed of the motor.

When a symmetrical three-phase alternating current is applied to the three-phase stator windings, a rotating magnetic field that rotates clockwise along the inner circular space of the stator and rotor at a synchronous speed n1 is generated. Since the rotating magnetic field rotates at a speed of n1, the rotor conductor is stationary at the beginning, so the rotor conductor will cut the stator rotating magnetic field to generate induced electromotive force (the direction of the induced electromotive force is determined by the right-hand rule). Because the two ends of the rotor conductor are short-circuited by the short-circuit ring, under the action of the induced electromotive force, an induced current that is basically the same as the direction of the induced electromotive force will be generated in the rotor conductor. The current-carrying conductor of the rotor is subjected to electromagnetic force in the stator magnetic field (the direction of the force is determined by the left-hand rule). The electromagnetic force generates electromagnetic torque on the rotor shaft and drives the rotor to rotate along the direction of the rotating magnetic field.

Through the above analysis, it can be concluded that the working principle of the motor is: when the three-phase stator windings of the motor (each phase differs by 120 degrees in electrical angle) are connected to the three-phase symmetrical alternating current, a rotating magnetic field will be generated. The rotating magnetic field cuts the rotor windings. Induction current is generated in the rotor winding (the rotor winding is a closed path), and the current-carrying rotor conductor will generate electromagnetic force under the action of the stator rotating magnetic field, thereby forming an electromagnetic torque on the motor shaft, driving the motor to rotate, and the direction of rotation of the motor The direction of the magnetic field is the same.

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