Guided By:

Mr. MUKUL SINGH

Presented By:

AMIT YADAV

ROLL NO- 13EE08

A Presentation on

CONTENTSHistory of eddy current

Introduction of Eddy Current

Eddy Current Brakes

Need of Eddy Current Braking

Principle Involved

Construction

Working principle

Types of Eddy Current Brakes

Applications

Advantages & Disadvantages

CONCLUSION

The first person to observe eddy current was FRANCOIS ARAGO (1786-1853) , the 25th prime minister of France, who was also a mathematician, physicist and astronomer.

In 1824 he observed the eddy current and called rotatory magnetism and that most conductive bodies could be magnetise and these discoveries were completed and explained by Mychael Faraday.

In 1834 , Heinrich Lenz stated Lenz’s Law , which say that the direction of induced current flow in an object will be such that it’s magnetic field will oppose the change of magnetic field that cause the current flow

• Eddy current are the loops of electrical current induced within conductors by a changing magnetic field in the conductor , due to faraday’s law of induction . Eddy current flows in closed loop within conductors , in plane perpendicular to the magnetic field .

• They can be induced within nearby stationary conductors by a time varying magnetic field created by an AC electromagnet or transformer, Or by relative motion between a magnet and a near by conductor

• The magnitude of the current in a given loop is proportional to the strength of the magnetic field, the area of the loop, and the rate of change of flux, and inversely proportional to the resistivity of the material.

• Definition → When a rotating conductor is moved

in a magnetic field a motional emf is generated. This

emf drives a current. The induced currents which

circulate inside a moving conductor are usually

called eddy currents.

Have inductance and thus induce magnetic fields.

Cause repulsion, attraction, heating effects etc.

• An eddy current brake, like a conventional friction brake, is a device used to slow or stop a moving object by dissipating its kinetic energy as heat. However, unlike electro-mechanical brakes, in which the drag force used to stop the moving object is provided by friction between two surfaces pressed together, the drag force in an eddy current brake is an electromagnetic force between a magnet and a nearby conductive object in relative motion, due to eddy currents induced in the conductor through electromagnetic induction.

• A linear eddy current brake in a German ICE 3high speed train in action

• In an eddy current brake the magnetic field may be created by a permanent magnet,

or an electromagnet so the braking force can be turned on and off or varied by

varying the electric current in the electromagnet's windings.

Eddy Current Brakes

• Makes use of the opposing tendency of eddy currents to inhibit the motion of a mechanical system.

Need for a braking system.

Abrasion FreeNo use of mechanical blocking, so there is no high levels of wear and tear &the life of systems remains same.

Eco friendly

No use of brake pad which produces debris.

High Braking ForceThis produces high braking forces to inhibit system

Principle involved

Principle involved

Faraday’s law of induction -:

• When a changing magnetic field is linked with a coil, an emf is induced in it. This change in magnetic field may be caused by changing the magnetic field strength by moving a magnet towards or away from the coil, or moving the coil into or out of the magnetic field as desired. Or in simple words, we can say that the magnitude of the emf induced in the circuit is proportional to the rate of change of flux.

Principle involvedLenz’s Law :

The direction of current induced in a conductor by a changing magnetic field due to Faraday's law of induction will be such that it will create a field that opposes the change that produced it.

• Lenz's law is shown by the negative sign in Faraday's law of induction:

which indicates that ε The induced voltage

ΦB the change in magnetic flux have opposite signs .

• It is a qualitative law that specifies the direction of induced current but says nothing about its magnitude. Lenz's Law explains the direction of many effects in electromagnetism, such as the direction of voltage induced in an inductor or wire loop by a changing current, or why eddy currents exert a drag force on moving objects in a magnetic field.

Construction

An eddy current brake basically consists of two members:

• A stationary magnetic field

• A solid rotatory disc

And the air gap between them

.

• An eddy current brake consists of a conductive piece of metal, either a straight bar or a disk, which moves through the magnetic field of a magnet, either a permanent magnet or an electromagnet When it moves past the stationary magnet, the magnet exerts a drag force on the metal which opposes its motion, due to circular electric currents called eddy currents induced in the metal by the magnetic field.

During braking, the metal disc is exposed to a magnetic field from an electromagnet, generated eddy current 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.

Types of Eddy Current Brakes

Circular eddy current brake

Linear eddy current brake

1.

2.

• Disk electromagnetic brakes are used on vehicles such as trains, and power tools such as circular saws, to stop the blade quickly when the power is turned off.

• A disk eddy current brake consists of a conductive non-ferromagnetic metal disc (rotor) attached to the axle of the vehicle's wheel, with an electromagnet located with its poles on each side of the disk, so the magnetic field passes through the disk. The electromagnet allows the braking force to be varied

• . When the driver steps on the brake pedal, current is passed through the electromagnet windings, creating a magnetic field, The larger the current in the winding, the larger the eddy currents and the stronger the braking force.

• Japanese Shinkansen trains had employed circular eddy current brake system on trailer cars since

100 Series Shinkansen.

japanese bullet train

• Linear eddy current brakes are used on some vehicles that ride on rails, such as trains. They are used on roller coasters, to stop the cars smoothly at the end of the

ride.

• The linear eddy current brake consists of a magnetic yoke with electrical coils positioned along the rail, which are being magnetized alternating as south and north magnetic poles. This magnet does not touch the rail, but is held at a constant small distance from the rail of approximately 7 mm

The kinetic energy of the moving vehicle is converted to heat by the eddy current flowing through the electrical resistance of the rail

Eddy current brakes on the Intamin roller coaster Goliath at WalibiHolland (Netherlands)

• They produce no smell or pollution (unlike friction brakes, which can release toxic chemicals into the environment).

• It uses electromagnetic force and not mechanical friction

• Non-mechanical (no moving parts, no friction)

• Fully resettable

• Can be activated at will via electrical signal

• Low maintenance

• Light weight

• Eddy-current brakes are quiet, frictionless, and wear-free, and require little or no maintenance

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.

• Need of electric power for the electromagnetism

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

• Recognizable uses for eddy currents are all around us. They exist in the home and in the work place. Here are some applications of the eddy current brake.

• Gym Equipment

• One of the most common places we may see eddy currents at work is while we’re putting ourselves to work. Exercise equipment utilizes this innovative technology in many ways.

• Popular equipment such as stationary exercise bikes elliptical machines and rowing machine are a great example of eddy currents in action

• Industrial Equipment

• Since the creation of eddy current braking systems, they have been adopted into many forms of useful technology and more importantly, industrial use. Power tools and large industrial machinery use this technology for several applications. One of the main uses for eddy current breaking is in emergency shut off.

Industrial factories and even common power tools have concerns with safety, which makes emergency shut off a must have. Moreover, if a power tool such, as a power saw or electric drill are shut off, the eddy currents kick in and safely bring the machine to a halt

Electromechanical meters are perhaps the most common place to find eddy current technology.

Rides and Roller CoastersExtreme uses for the eddy current brake are seen in amusement parks and entertainment centers all over. Whether this is in roller coasters or other rides, braking technology such as this is vital to amusement parks around the world.

Modern roller coasters adapted this kind of technology to allow for a smoother and safer stop for its riders. The high-speed experience makes for maximum fun but also requires an extremely safe braking system such as the eddy current breaking system

High Speed Electric Trains

• Transportation technology has adopted the innovations in eddy current braking to create safer braking systems and new high-speed railways. Eddy current braking is a remarkable option for transit systems because of its low cost of maintenance and resistance to harsh weather conditions.

• Eddy currents are a safe way to decelerate a moving train while providing constant comfort and ease for passengers. By adopting this type of technology, commuter, high-speed, and even streetcar trains have been able to reach new speeds and provide safety levels that are better than

before.

CONCLUSION

• ECB is a good invention for speed control of high speed vehicles.

• It makes use of opposing tendency of EDDY CURRENT

We can control the high speed vehicles without wear and tear in itsparts.

Drawback of ordinary mechanical braking system can be overcomeby application of ECB

• In future ordinary brakes will be replaced by the ECB completely.

• By the use of ECB in future we can control high speed train completely.

• By some new invention of extra mechanism we can use ECB for slow speed

vehicles also.