The Working Principle of Linear Induction Motor.docx

Linear induction motors evolved from rotary motors. When a three-phase (or polyphase) winding on the primary side is passed through a symmetrical sinusoidal alternating current, an air-gap magnetic field is created. When the longitudinal edge effect caused by the fracture at both ends of the iron core is not considered, the distribution of the air gap magnetic field is similar to that of a rotating electrical machine, which is sinusoidally distributed along a straight line. But instead of rotating, it translates along a straight line, called a traveling-wave magnetic field. Obviously, the moving speed of the traveling-wave magnetic field is the same as the linear speed of the rotating magnetic field on the inner surface of the stator, and the moving speed of the traveling-wave magnetic field is called the synchronous speed.

Below is the list

The physics of induction motors

Difference Between Linear Induction Motor and Rotary Induction Motor

The physics of induction motors

When the traveling wave magnetic field cuts the secondary side rod, induced electromotive force and current will be generated in the rod, and the current of the rod interacts with the air gap magnetic field to generate a tangential electromagnetic force. If the primary side is fixed, the secondary side will move in a straight line along the moving direction of the traveling wave magnetic field under the action of this electromagnetic force. It can be seen that changing the pole distance or power frequency can change the movement speed of the secondary side; changing the energization phase sequence of the primary winding can change the movement direction of the secondary side.

Difference Between Linear Induction Motor and Rotary Induction Motor

There is no essential difference between linear induction motors and rotary induction motors in terms of industrial principles, except that the mechanical movements produced are different. However, there are big differences in electromagnetic performance between the two, mainly in the following three aspects:

1. The three-phase windings of the stator of the rotating induction motor are symmetrical, so if the applied three-phase voltage is symmetrical, the three-phase current is symmetrical. But the primary three-phase winding of the linear induction motor is asymmetric in space, and the inductance value of the coil located at the edge is very different from the inductance value of the coil located in the middle. That is to say: the phase reactances are not equal. Therefore, even though the three-phase voltages are symmetrical, the three-phase winding currents are not symmetrical.

2. The air gap between the stator and the rotor of the rotary induction motor is circular, with no head and no tail, and is continuous. There is no beginning or end. But the air gap between the primary and secondary of a linear induction motor has a beginning and an end. When one end of the secondary enters or leaves the air gap, additional current is induced in the secondary conductor, known as "edge effect". Due to the influence of edge effects, the operating characteristics of linear induction motors and rotary induction motors are very different.

3. Since the linear induction motor has a certain length between the primary and the secondary in the linear direction, the air gap between the primary and the secondary will generally be longer in terms of mechanical structure. Therefore, its power factor is lower than that of a rotating induction motor.

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