Linear Induction Motor (LIM)

Linear Induction Motor (LIM): 

The linear induction motor, which has been abbreviated as LIM. The Linear induction motor is basically used for a special purpose motor, which is in use to achieve rectilinear speed rather than the speed of rotation in the case of conventional motors. This is an engineering miracle, for a particular purpose, to replace a normal motor with more or less similar work principle, thus increasing its versatility of operation. First, we look at the construction of a linear induction motor. 

Construction of linear induction motor:

According to the construction, LIM is almost similar to the construction of three-phase conventional induction motor. 

In the construction of linear induction motor, the stator and Rotor respectively is known as the primary and secondary. 

It forms the primary of the linear induction motor housing for the field system, if the stator of the poly-phase induction motor is cut along the section and laid on a flat surface, and consequently the rotor forms the secondary of LIM. For effective flux linkage, it consisting of flat aluminium conductors with a ferromagnetic core. 

Another type of LIM use is called a double-sided linear induction motor or DLIM. For the most effective use of both side-of-flow, there are either a primary turn on either side of the secondary.

Working of a Linear induction motor:

When the primary of three-phase LIM is energised by the power supply, the travelling flux is induced in the primary rather than the rotating, which travels with the entire length of the primary. Due to the relative motion between the travelling flux and conductors, electric current is induced into the aluminium conductors of the secondary. To produce thrust or linear force, this induced current interacts with the travelling flux wave.

If a secondary is fixed and the primary is free, the force will move in the direction of force, resulting in the required linear motion. 

When the supply is given, the synchronous motion of the field is given by the equation:

Ns= 2fs/p

Where, fs= Supply frequency (Hz)

p = Number of poles.

Ns = Synchronous speed of RMF (rpm)

This rotating magnetic field will results in linear travelling field.

Because of this field, velocity is given by,

Vs = 2tfs (m/sec)  

Where, t = polepitch

for S slip,

V = (1-S)Vs

Application of Linear induction motor:

A linear induction motor is not more useful than a conventional motor, but there are many examples that LIM is really essential for some specialised operations. Some of the applications of a Linear induction motor are as follows.

1) The automatic door in the electric trains

2) Pumping 

3) Material handling in cranes

4) Metal conveyor belt