Linear Induction Motor

CONTENTS

• INTRODUCTION

• CONSTRUCTION

• OPERATION

• APPLICATIONS

• ADVANTAGES

• LIMITATIONS

Linear Induction Motor

linear induction motor that produces direct linear force instead of torque.

linear induction motor can be visualized by considering squirrel cage induction motor split radially along its axis of rotation and flatten out .This results in flat “stator,” or upper section.Rotor or lower section consists of a continuous copper or aluminum sheet placed.

Construction

primary coil assembly and secondary (reaction plate )

How to construct?

5

TableForcer (coil)

Linear encoder

LinearGuideCable carrier

Shaft support

Linear Shaft MotorLinear induction motor coupled to Shaft

Actual stage (Moving Forcer)

6

Linear induction motor coupled to shaft

Linear guide

Table

Encoder

Shaft Support

OPERATION

Linear Induction Motor• non-contacting, high speed, linear motor

that operates on the same principle as a rotary, squirrel cage, induction motor.

• used in applications where accurate positioning is not required.

Forces Produced

Forces Produced

• LEM’s develop two mutually perpendicular forces, one in the direction of motion and the other normal to the direction of motion.

• The normal force may be an attraction or a repulsion force between the primary and secondary. A machine in which the net force is such that the secondary tends to be suspended over the primary may be used mainly for suspension and called a linear levitation machine (LLM).

• Both LIM’s and LSM’s may be used a levitation or as linear motors.

Applications on maglev vehicles

•The principle of a maglev train is that floats on a magnetic field and is propelled by a linear induction motor. A maglev train floats about 10mm above the guide way on a magnetic field. It is propelled by the guide way itself rather than an onboard engine by changing magnetic fields.

MAGLEV VEHICLE CONSTRUCTION

• BASICALLY THE CONSTRUCTION DEPENDS ON 2 DIFFERENT FORCES

• PROPULSION FORCE

• LEVITATING FORCE

PROPULSION FORCE

• This is a horizontal force which causes the movement of train.

It requires 3 parameters.

• Large electric power supply• Metal coil lining, a guide way

or track.• Large magnet attached

under the vehicle.

PROPULSION FORCE

• A repulsive force and an attractive force induced between the magnets are used to propel the vehicle (superconducting magnet).

• The propulsion coils located on the sidewalls on both sides of the guideway are energized by a three-phase alternating current from a substation, creating a shifting magnetic field on the guideway.

• The on-board superconducting magnets are attracted and pushed by the shifting field, propelling the Maglev vehicle

LEVITATING FORCE

When a moving permanent magnet sweeps across a conducting ladder, two types of force are produced.

Horizontal tractive force. Vertical force which tends to push

the magnet away from the ladder.

At low speed the voltage induced

in the conductor(A) is maximum because flux is greatest at the centre of north pole. As this current flows via Conductors B and C,it produces induced SSS and NNN poles.

Since the distribution of SSS and NNN pole is symmetrical w.r.t centre of the magnet, the vertical and repulsion force cancel eachother.

• At high speed N pole of the magnet lies over the induced NNN pole, which pushes it upwards with a strong vertical force.

HOW THE VEHICLE LEVITATES

The levitating force is the upward thrust which lifts the vehicle in the air.

There are 2 types of levitating systems

1. EDS system

2. EMS system

WORKING OF MAGLEV

1.EMS SYSTEM

Maglev concepts using electro -magnetic suspension employ attractive forces.

Magnetic fields inside and outside the vehicle are insignificant; proven, commercially available technology that can attain very high speeds (500 km/h); no wheels or secondary propulsion system needed.

The separation between the vehicle and the guideway must be constantly monitored and corrected by computer systems to avoid collision due to the unstable nature of electromagnetic attraction.

2.EDS SYSTEM

In EDS both the rail and the train exert a magnetic field, and the train is levitated by the repulsive force between these magnetic fields.

At slow speeds, the current induced in these coils and the resultant magnetic flux is not large enough to support the weight of the train. For this reason the train must have wheels or some other form of landing gear to support the train until it reaches a speed that can sustain levitation.

Onboard magnets and large margin between rail and train enable highest Onboard magnets and large margin between rail and train enable highest recorded train speeds (581 km/h)recorded train speeds (581 km/h).This system is inherently stableMagnetic shielding for suppression of strong magnetic fields and wheels for travel at low speed are required.It can’t produce the propulsion force. So, LIM system is required.

On-the-Fly Welder

Appllications

• On-the-Fly WelderThe controller receives velocity and position data from an

incremental encoder mounted to a roller on the conveyor belt.

The secondary motor/drive system receives instructions from the controller, based on a ratio of the velocity and position information

supplied by the primary system encoder. The linear motor forcer carries the weld head and is

mounted on an overhead platform in line with the conveyor.

.

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• Capsule Filling

Machine

Advantages

Rotary vs. Linear Motors

Linear MotorRotary/ Linear

ConversionDirect thrust Rotary to linear

mechanism requiredMinimal maintenance

More maintenance

No internal moving parts

More wear

Virtually silent operation

Noisy

Very low inertia Higher inertiaHigher Cost Low CostLess Common Widely Used

Advantages

• Small, compact – fits into smaller spaces• No backlash from gears or slippage from

belts – provides smooth operation• Reliability – non-contact operation reduces

component wear and reduces maintenance• Wide speed range • Designs are available with either a moving

coil or moving magnets.• Ease of Control and Installation

Limitations

• Costly to purchase and install

• Force Per Package Size: Linear motors are not compact force motors compared to a rotary motor.

• Heating: The forcer is often attached to the load. If an application is sensitive to heat, thermal management techniques need to be applied.

References

• IEEE,applications of linear induction motor to high speed transport system.

• http://science.howstuffworks.com/maglev-train.htm

• http://future.wikia.com/wiki/Maglev_train• http://www.geocities.com/nastywik/trains.h

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Thank you