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Eddy Current Brakes 2013-2014

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TABLE OF CONTENTS

Acknowledgement ............................................................................................. 2

Abstract ............................................................................................................. 3

History ............................................................................................................... 4

Introduction ....................................................................................................... 5

Eddy Current Brakes .......................................................................................... 6

Principle of Operation ........................................................................................ 7

Types of Eddy Current Brakes ............................................................................ 8

Parameters Affecting Eddy Current.................................................................. 11

Advantages ...................................................................................................... 14

Applications ..................................................................................................... 15

Future Scope .................................................................................................... 16

Conclusion ....................................................................................................... 17

Reference ........................................................................................................ 18

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ACKNOWLEDGEMENT

With all due respect, I sincerely express my gratitude to our

beloved Head of the Department, Smt. Lizz Joseph, for her blessings

and undying support.

May I thank all the department faculties too, who have been

there to help me whenever I needed them.

I also sincerely thank my seminar guide, Smt. Tinu Scaria

(Lecturer) for her cooperation and assistance

At this juncture, I also wish to whole-heartedly thank all my

friends for their encouragement and good wishes, and for all the

unforgettable experiences shared while searching for a topic.

I also thank the LORD ALMIGHTY without his will this paper

could not have materialized.

Ajith.A

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ABSTRACT

Many of the ordinary brakes, which are being used now

days, stop the vehicle by means of mechanical blocking. Thiscauses skidding and wear and tear of the vehicle. And if the

speed of the vehicle is very high, the brake cannot provide that

much high braking force and it will cause problems. These

drawbacks of ordinary brakes can be overcome by a simple

and effective mechanism of braking system 'The eddy current

brake'. It is an abrasion-free method for braking of vehicles

including trains. It makes use of the opposing tendency of eddy

current Eddy current is the swirling current produced in a

conductor, which is subjected to a change in magnetic field.

Because of the tendency of eddy currents to oppose, eddy

currents cause energy to be lost. More accurately, eddy

currents transform more useful forms of energy such as kinetic

energy into heat, which is much less useful. In many

applications, the loss of useful energy is not particularly

desirable. But there are some practical applications. Such an

application is the eddy current brake.

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HISTORY

The first person to observe current eddies was Franois Arago

(1786-1853), the 25th

president of the France, who was also a

mathematician, physicist and astronomer. In 1824 he observed what

has been called rotator magnetism and the fact that most conductive

bodies could be magnetized; these discoveries were completed and

explained by Michael Faraday (1791-1867).

In 1834, Heinrich Lenz stated the Lenzs Law, which states that

the direction of the induced current flows in an object will be such

that its magnetic field will oppose the magnetic field that caused the

current flow. Eddy currents develop secondary flux that cancels a

part of the external flux.

French physicist, Lacoun Foucault (1819-1861) is credited with

having discovered Eddy currents. In September, 1855, he discovered

that the force required for the rotation of a copper disc becomes

greater when it is made to rotate with its rim between the poles of

magnet, the disc at the same time becoming heated by the eddy

current induced in the metal. The first use of eddy current for Non-

destructive testing occurred in 1879, when D.E. Hughes used the

principles to conduct metallurgical sorting testing.

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INTRODUCTION

Many of the ordinary brakes, which are being used now days

stop the vehicle by means of mechanical blocking. These causes

skidding and wear & tear of the vehicle. And if the speed of the

vehicle is very high, the brake cannot provide that much high braking

force and it will cause problems. These drawbacks of ordinary brakes

can be overcome by a simple and effective mechanism of braking

system 'The eddy current brake'. It is an abrasion-free method for

braking of vehicles including trains. It makes use of the opposing

tendency of eddy current Eddy current is the swirling current

produced in a conductor, which is subjected to a change in magnetic

field. Because of the tendency of eddy currents to oppose, eddy

currents cause energy to be lost. More accurately, eddy currentstransform more useful forms of energy such as kinetic energy into

heat, which is much less useful. In many applications, the loss of

useful energy is not particularly desirable. But there are some

practical applications. Such an application is the eddy current brake.

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EDDY CURRENT BRAKES

Eddy current brakes are simple magnetic devices that consist of

a non-ferromagnetic conductor that moves through a magnetic field.

Where a magnetic field is created in the gap of a toroidal

electromagnet, with diameter D. When the conductive disc rotates,

eddy currents are induced at an average distance R from the axis of

rotation where the poles magnetic field moves as a function of the

angular velocity of the disk.1 Power is dissipated in the conductive

disk by the Joule Effect, which creates a viscous-like torque applied

to the disk.

Above figure is the sketch of eddy currents in a rotating disc.

The crosses represent a steady magnetic field perpendicular to the

plane of the disc. According to Faradays law, eddy currents appear

in those points of the disc where the magnetic field increases or

decreases.

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PRINCIPLE OF OPERATION

Eddy current brake works according to Faraday's law of

electromagnetic induction. According to this law, whenever a

conductor cuts magnetic lines of forces, an emf is induced in the

conductor, the magnitude of which is proportional to the strength of

magnetic field and the speed of the conductor. If the conductor is a

disc, there will be circulatory currents i.e. eddy currents in the disc.

According to Lenz's law, the direction of the current is in such a way

as to oppose the cause, i.e. movement of the disc.

Essentially the eddy current brake consists of two parts, a

stationary magnetic field system and a solid rotating part, which

include a metal disc. During braking, the metal disc is exposed to a

magnetic field from an electromagnet, generating eddy currents inthe 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.

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TYPES OF EDDY CURRENT BRAKES

Electromagnetic brakes are similar to electrical motors; non-

ferromagnetic metal discs (rotors) are connected to a rotating coil,

and a magnetic field between the rotor and the coil creates a

resistance used to generate electricity or heat. 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.

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

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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 metalthrough 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

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

heat in rotors.

Eddy current brakes at the Intamin roller coaster Goliath

in Walibi World (Netherlands). The first train in commercial

circulation to use such a braking is the ICE 3. Modern roller

coasters use this type of braking, but utilize permanent

magnets instead of electromagnets, and require no electricity.

However, their braking strength cannot be adjusted.

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PARAMETERS AFFECTING EDDY CURRENT

Braking Time of the Disc

First of all, the time necessary for the disc to completely

stop from a fixed initial angular speed when the motor is

turned off can be measured as a function of the excitation

intensity. We must keep in mind that the larger the excitation

intensity is selected, the larger the voltage applied to the motor

must be to achieve that initial speed. Error bars have been set

to 0.3 s, a typical uncertainty when using stopwatches.

Equation (1) implies that the eddy current braking torque is

proportional to the instantaneous angular speed. However, the

results plotted in figure 3 are not suitable for verifying this fact,

due to the lack of a known model for the internal braking

torque acting on the motor. Therefore, the result of this first

experiment cannot be numerically tested.

Braking time for the copper disc versus excitation intensity.

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Eddy Current Losses versus Angular Velocity

To test the proportionality between Pe and 2 shown by

equation (1) a fixed excitation intensity Iex must be chosen.

Then the voltage supplied by the power source of the motor

must be varied in order to select various angular speeds. For

any chosen speed of the disc the power consumption of the

motor Pm (Iex, ) can be calculated as the product of its

voltage and intensity. The power consumption Pm (0, ) when

the electromagnet is turned off must be computed in the same

way. Then the power dissipated only by eddy currents is simply:

Pe () = Pm (Iex, )Pm (0, ) (Iex fixed).

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From the above it may be deduced that:

Eddy current brakes are an effective means of regulating

train speed at higher line speeds.

The brake effort can be regulated and varied to provide

both service and emergency braking modes.

The infrastructure will need to be adapted for the use of

eddy current brakes.

Physical clearance must exist between track structure and

the eddy current brake head.

Electromagnetic compatibility issues with track mounted

and line side equipment must be addressed.

The track resistance to longitudinal, vertical and lateral

forces must be considered and that this will place

additional requirements on the design and construction

of the track.

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ADVANTAGES

The device can be used in heavy automobile as an accessory.

It is highly at high speed

It works on electricity and consumes very small amount of

power for a tiny time period

Can be easily controlled and resettable

Very light weight and low maintenance

Consumes small space therefore installation is easy

Running cost is small

Disadvantages

Higher running cost

Very large amount of heat generation

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APPLICATIONS

Used in the braking system of roller coaster.

Used in the braking system high speed train

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FUTURE SCOPE

The eddy current increases with decreases in resistivity of

material. There is a slope of applying Cu wire winding of AWG

20.08 less to get highly conductive surface and minimum

resistance possible to increase the eddy current induced.

The magnetic field induced by electromagnet is not too large

and can be increased by supplying higher current.

Speed of shaft can be increased by providing a gear

arrangement instead of chain sprocket assembly of high gear

ratios to get higher speeds.

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CONCLUSION

The eddy current brakes can be used as an accessory in heavy

automobiles with conventional friction brakes; because it is the

remedy of problems faced by any conventional brakes like

fading skidding, requirement of servo mechanism breaking,

higher weights etc.

This device is easy to install and cost incurred is small so can be

used in the automobiles manufactured.

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REFERENCE

www.freepatentonline.com

www.wikipedia.com

www.eddycurrentbrake.com

www.railwaygazette.com

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