Linear Induction Motor

July 11, 2020
Linear induction motor

From the name linear, we can deduce that this is a rotary motor that has been cut and unrolled to provide us with linear (straight line) motion and force instead of rotational torque. In this motor, we have an unwrapped stator spread out flat, called the motor’s primary.

The rotor consists of a flat aluminum conductor with a ferromagnetic core, and it moves in a straight line past the stator.

It’s important to know where we could find the linear motor before understanding how it works; Let’s see.

Applications of Linear Induction Motor

Because of the economic aspects and versatility of usage of the linear motor, we may find it in several applications that require rapid movement of a large payload. The following are some examples.

  • With overhead traveling cranes for moving sheet metal.
  • It is used to drive conveyors, textile shuttles, sliding doors, and machine tools.
  • In electrical trains represented in the automatic sliding doors.
  • In mechanical handling equipment.
  • It’s used as electromagnetic Pumps as a liquid metal.
  • Metallic conveyor belts.
  • It’s also used in high voltage circuit breakers and accelerators.

Working Principle of a Linear Induction Motor

When we supply the linear motor’s primary with a three-phase supply, a flux is produced that travels across the length of this primary. Due to the relative motion between the flux and the aluminum conductor, a current will generate in this conductor and interacts with the traveling flux to produce a linear force.

If we fix the motor’s secondary and make the primary free, the linear force will cause the primary to move in the traveling wave’s direction to result in the required rectilinear motion.

Working principle of a linear induction motor

I think some equations will make it easier to understand;

When we give supply to the motor, we will have a synchronous speed of the field

ns=2fs/P

Where

ns: the synchronous speed of rotation of the magnetic field (revolutions/sec)

fs: the supply frequency (HZ)

P: Number of poles

And the velocity of the linear traveling field produced as a result of the field

Vs=2tfs (m/sec)

Where

t: the pole pitch

And for a slip (S) the speed of the linear motor will be

V=(1-s) Vs

From these equations, we can understand that the linear motor’s speed depends on the source’s frequency. Thus, when we change the input frequency we control the speed of the motor.

It’s important to know that the linear induction motor requires a large air gap to have a more significant magnetizing current. However, at the same time, the power factor and efficiency are lower.

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