CONTENTS :~

Introduction of eddy current

Introduction of eddy current brake

Components And Operational Features Of Eddy Current Brakes

How eddy current brake works?

Advantages Disadvantages Applications Conclusion

INTRODUCTION OF EDDY CURRENT

Eddy currents are electric currents induced in conductors when exposed to a changing magnetic field; due to relative motion of the field source and conductor or due to variations of the field with time.

This can cause a circulating flow of electrons, or current, within the body of the conductor.

These circulating eddies of current have inductance and thus induce magnetic fields. 

� Eddy current brakes, like conventional friction brakes, are responsible for slowing an object, such as rotating machinery, a moving train, or even a roller coaster.These brakes make use of opposing tendency of eddy currents. The drawbacks of ordinary brakes which uses mechanical blocking could be eliminated by use of a more simple and effective mechanism known as eddy current brakes.

� There are two basic types: (1)circular

(2)linear

Introduction Of Eddy Current Brake

LINEAR EDDY CURRENT BRAKES 

It consists of a magnetic yoke with electrical coils which are being magnetized alternately.

This magnet does not touch the rail (held at approx 7 mm.) 

When the magnet is moved along the rail, it generates a non-stationary magnetic field which generates electrical tension and causes eddy currents.

These disturb the magnetic field in such a way that the magnetic force is diverted to the opposite of the direction of the movement. 

The braking energy of the vehicle is converted in eddy current losses which lead to a warming of the rail.

 

CIRCULAR EDDY CURRENT BRAKES When electromagnets are used, control of the

braking action is made possible by varying the strength of the magnetic field.

A braking force is possible when electric current is passed through the electromagnets. The movement of the metal through the magnetic field of the electromagnets creates eddy currents in the discs.

These eddy currents generate an opposing magnetic field, which then resists the rotation of the discs, providing braking force.

The net result is to convert the motion of the rotors into heat in the rotors.

Circular Eddy Current Brakes:-

Electromagnets Cast Iron Core Conducting (Copper) Wire Mounting bolts Disc Mild steel machined from plates

Essentially the eddy current brake consists of two parts, a stationary magnetic field system and a solid rotating part, which include a metal disc.

Two members are separated by a short air gap, they're being no contact between the two for the purpose of torque transmission. Consequently there is no wear as in friction brake.

COMPONENTS AND CONSTRUCTIONAL

FEATURES OF EDDY CURRENT BRAKES:-

Stator consists of pole core, pole shoe, and field winding.

The field winding is wounded on the pole core. Pole core and pole shoes are made of east steel laminations and fixed to the state of frames by means of screw or bolts.

Copper and aluminum is used as winding materials.During braking, the metal disc is exposed to a magnetic field from an electromagnet, generating eddy currents in the disc. The magnetic interaction between the applied field and the eddy currents slow down the rotating disc. Thus the wheels of the vehicle also slow down since the wheels are directly coupled to the disc of the eddy current brake, thus producing smooth stopping motion.

Working Principle

Linear Eddy Current Brakes:-

HOW DOES AN EDDY CURRENT BRAKE STOP SOMETHING MOVING?

Suppose we have a huge solid block of copper mounted on wheels. It is moving at a very high speed and we need to stop it.

Suppose we place a giant magnet next to the track so that train had to pass nearby.

As the copper approached the magnet eddy currents would be generated inside the copper which would produce their own magnetic field.

As the front passed by, slowing down, the currents there would reverse, generating an attractive magnetic field that tried to pull the train back again. (again, slowing it down). The copper would heat up the eddy currents swirled inside it, gaining the kinetic energy lost by the train as it slowed down.

As the front part approached the magnet eddy currents in that bit of copper would try to generate a repulsive magnetic field to slow down copper’s approach to magnet.

Eddy current brakes develop torque by the direct magnetic linking of the rotor to the stator.

This linking generates eddy currents in the driven rotor.

Eddy current brakes must have a slip between the rotor and the stator to generate torque.

An eddy current brake having an electromagnetic pole and the rotor is positioned in close proximity to the stator with an air gap between them

Electromagnets produce magnetic field from supplied current

Change of magnetic flux (with time) induces eddy currents in conductor (disc)

Eddy Currents produce another magnetic field opposing first field

Opposing magnetic fields create force that reduces velocity

(Arrangement of ECB in high speed trains)

ADVANTAGES It uses electromagnetic force and not

mechanical friction  Non-mechanical (no moving parts, no friction) Can be activated at will via electrical signal Low maintenance Operates at any rotational speed Light weight Eddy-current brakes are quiet, frictionless, and

wear-free, and require little or no maintenance. They produce no smell or pollution (unlike

friction brakes, which can release toxic chemicals into the environment). All this makes them much more attractive than noisy

friction brakes that need regular inspection and routinely wear out. It's been estimated that switching an electric train from friction brakes to eddy-current brakes could halve the cost of brake operation and maintenance over its lifetime.

DISADVANTAGES. . .

Braking force diminishes as speed diminishes with no ability to hold the load in position at standstill.

That could be considered to be a safety issue, but it really means that friction braking may need to be used as well.

Eddy-current brakes can only be used where the infrastructure has been modified to accept them.

It can not be used at low speed vehicles or vehicle running at low speed

APPLICATIONS:- For additional safety on long decants in mountain area Eddy current brakes are best substitutes for ordinary

brakes, which are being used nowadays in road vehicles even in trains, because of their jerk-free operation.

In mountain areas where continuous braking force is needed, for a long time, the eddy current braking is very much useful for working without overheating.

Eddy current brakes are very much useful for high-speed passengers and good vehicles.

It can also be used to slow down the trolleys of faster roller coasters.

There are a number of major commercial applications of eddy current brake technology in the mining, railroad, and elevator industries.

We'll also find eddy current brakes in all kinds of machines, such as circular saws and other power equipment. And they're used in things like rowing machines and gym machines to apply extra resistance to the moving parts so your muscles have to work harder.

CONCLUSION:-

The ordinary brakes which are being used now a days stop the vehicle by means of mechanical blocking. This may cause skidding and wear and tear of the vehicle.

And if the speed of the vehicle is very high the brake could not provide that much high braking force and it will cause problems.

These drawbacks can be eliminated by using a simple and effective mechanism of braking system called eddy current brakes.

It is an abrasion free method for braking of vehicles including trains.

It makes use of opposing tendency of eddy currents.

THE END

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