The precondition for the three-phase asynchronous motor to rotate is to have a rotating magnetic field. The stator winding of the three-phase asynchronous motor is used to generate the rotating magnetic field. We know, but the voltage between phases of the phase power supply is 120 degrees different in phase. The three windings in the stator of three-phase asynchronous motor are also 120 degrees different from each other in spatial orientation, so when the three-phase power supply is connected in the stator winding, the stator winding will produce a rotating magnetic field, which is divided into four moments to describe the generation process of the rotating magnetic field. For each cycle of current change, the rotating magnetic field rotates once in space, that is to say, the rotating speed of the rotating magnetic field is synchronous with the change of current. The rotating speed of the rotating magnetic field is: n = 60F / P, where f is the power frequency, P is the pole number of the magnetic field, and N is in revolutions per minute. Three phase asynchronous motor for motor operation. The rotating speed of the three-phase asynchronous motor rotor is lower than that of the rotating magnetic field. Because of the relative motion between the rotor winding and the magnetic field, the electromotive force and current are induced, and the electromagnetic torque is generated by the interaction between the rotor winding and the magnetic field to realize the energy transformation. Compared with single-phase asynchronous motor, three-phase asynchronous motor has better performance and can save various materials. According to different rotor structure, three-phase asynchronous motor can be divided into cage type and winding type. Cage rotor asynchronous motor has been widely used because of its simple structure, reliable operation, light weight and low price. Its main disadvantage is the difficulty of speed regulation. The rotor and stator of wound three-phase asynchronous motor are also provided with three-phase winding and connected with external rheostat through slip ring and brush. Adjusting the rheostat resistance can improve the starting performance and speed of the motor. According to this formula, we know that the speed of the motor is related to the number of poles and the frequency of the power supply. Therefore, there are two ways to control the speed of the AC motor: 1. Change the pole method. 2. Frequency conversion method. In the past, more than * methods were used, but now frequency conversion technology is used to realize CVT control of AC motor. The direction of rotation of the rotating magnetic field is related to the phase sequence of the current in the winding. Phase sequence a, B and C are arranged in a clockwise direction, and the magnetic field rotates in a clockwise direction. If any two of the three power lines are exchanged, for example, if phase B current is connected to phase C winding and phase C current is connected to phase B winding, then the phase sequence becomes: C, B and a, then the magnetic field must rotate in a counterclockwise direction. Using this characteristic, we can easily change the rotation direction of three-phase motor. After the stator winding generates the rotating magnetic field, the rotor guide bar (squirrel cage bar) will cut the magnetic field line of the rotating magnetic field and generate the induced current. The current in the rotor guide bar interacts with the rotating magnetic field to generate the electromagnetic force. The electromagnetic torque generated by the electromagnetic force drives the rotor to rotate along the rotating magnetic field direction at the speed of N1. In general, the actual speed n1 of the motor is lower than the speed n of the rotating magnetic field. Because assuming n = N1, there will be no relative movement between the rotor bar and the rotating magnetic field, the magnetic field line will not be cut, and the electromagnetic torque will not be generated, so the rotor speed n1 must be less than n. So we call three-phase motor asynchronous motor.