Induction motor, also known as "asynchronous motor", is a device that puts the rotor in a rotating magnetic field and obtains a rotating torque under the action of the rotating magnetic field, so that the rotor rotates. The rotor is a rotatable conductor, usually in the shape of a squirrel cage.
Through the relative movement of the rotating magnetic field generated by the stator (its speed is the synchronous speed n1) and the rotor winding, the rotor winding cuts the magnetic induction line to generate an induced electromotive force, thereby causing an induced current in the rotor winding. The induced current in the rotor winding interacts with the magnetic field to generate electromagnetic torque, which makes the rotor rotate. As the rotor speed gradually approaches the synchronous speed, the induced current gradually decreases, and the generated electromagnetic torque is also reduced accordingly. When the asynchronous motor is working in the motor state, the rotor speed is less than the synchronous speed. In order to describe the difference between the rotor speed n and the synchronous speed n1, slip is introduced.
Because the rotating magnetic field continuously cuts the closed conductor in the rotor, induced electromotive force and induced current are generated, and then the electromagnetic torque is generated by the interaction of the induced current in the rotor and the rotating magnetic field, so that the rotor rotates in the same direction with the direction of the rotating magnetic field. For example, a cage-type asynchronous motor, because the rotating magnetic field cuts the rotor conductor clockwise, which is equivalent to the conductor rotating counterclockwise. Using the right-hand rule, let the magnetic line of induction pass through the palm of the hand perpendicularly, and the thumb points to the direction of the conductor. The four fingers are the induced current. (As shown in the figure, the direction of the rotor winding current of the cage asynchronous motor), and then apply the left-hand rule, the magnetic line of induction passes through the palm of the hand, and the four fingers point to the direction of current movement. The thumb direction is the direction in which the rotor receives the electromagnetic force ( As shown in the figure, the electromagnetic torque torque T direction), the electromagnetic torque is formed under the action of electromagnetic force, which drags the rotor to rotate in the direction of the rotating magnetic field.
Sectional view of cage asynchronous motor
In an asynchronous motor, in order to keep the rotating magnetic field always cutting the rotor conductor to generate an induced current, the rotor speed is lower than the speed of the rotating magnetic field.
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