EDDY CURRENT BRAKES

• By: CHANDAN KUMAR 10104EN058

• Critic: BANSHI LAL SONI 10104EN057

What is meaning of Eddy?• Eddy means the circular movement of water causing a

small whirlpool.

What is Eddy Current?• It is a swirling current set up in a conductor in response

to a changing magnetic field. • By Lenz's law, the current swirls in such a way as to

create a magnetic field opposing the change.

Introduction :

• Eddy currents are one of the most outstanding electromagnetic induction phenomena.

• Sometimes they are undesirable because of their dissipative nature (e.g. transformer core, metallic parts of generator and motor etc.)

• In many other cases, however, eddy currents are valuable (metal detectors, coin recognition system in vending machine, electricity meters, induction ovens etc )

Eddy Current Brakes :• Eddy current brakes are simple magnetic devices that

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

• In the above figure, a magnetic field is created in the gap of the electromagnet, with diameter D. When the conducting disk rotates, eddy currents are produced in the disc.

• Power is dissipated in the conducting disk by Joule Effect, which create a torque applied to the disk.

Principle of Operation :

• Eddy current brake works according to Faraday's law of electromagnetic induction.

• When 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.

Theoretical Foundation :• Current is induced in an electrical conductor when it

undergoes conditions of variable magnetic flux

• There are two basic procedures to achieve such conditions: (i) exerting a time-varying magnetic field on a static

conductor. (ii) exerting a steady magnetic field on a moving conductor.

Power dissipated when conductor is moving :

• Since the magnetic field B is steady, the induced electric field on each point of the disk in given by:

Here, v is velocity

• Instead of measuring B directly, it is related to the excitation current it Iex in the coil.

B α Iex From this equation : E α ω Iex

• Now, power dissipated in a loop is proportional to square of EMF and to the inverse of electrical resistivity.

Pe = K ω2 Iex2

ρ

Existing Braking Methods :• Drum Brakes: A drum brake is a brake that uses friction caused by a set of shoes or pads that press against a rotating drum-shaped part called a brake drum.

• Disc Brake:A disc brake is a wheel brake which slows rotation of the wheel by the friction caused by pushing brake pads against a brake disc with a set of calipers. The brake disc is usually made of cast iron, but may in some cases be made of composites such as reinforced carbon or ceramic matrix composites.

• Hydraulic brake:The hydraulic brake is an arrangement of braking mechanism which uses brake fluid, typically containing ethylene glycol, to transfer pressure from the controlling mechanism to the braking mechanism.

• Anti-Lock Braking System:ABS is an automobile safety system that allows the wheels on a motor vehicle to maintain tractive contact with the road surface , preventing the wheels from locking up (ceasing rotation) and avoiding uncontrolled skidding. It is an automated system that uses the principles of threshold braking and cadence braking.

Pros :• It uses electromagnetic force and not mechanical friction• Can be activated at will via electrical signal• Low maintenance• Light weight• High impact• Less noise• Simple in design• High degree of safety

Cons :• Braking force diminishes as speed diminishes with no

ability to hold the load in position at standstill. • Usage of electric power for braking• Less effective under very low velocities• Eddy-current brakes can only be used where the

infrastructure has been modified to accept them

Application :• Already in use under some railway system

An eddy current brake of a German ICE 3 in action• as additional retarder for aircrafts• May also find application in virtually any rotating system which have

metallic parts

• Equally applicable to heavy and light vehicles• Can be used as additional retarder for aircrafts• May also find application in virtually any rotating system

which have metallic parts

Conclusion :• The ordinary brakes which are being used now days,

stop the vehicle by means of mechanical blocking. This causes skidding and wear and tear of the vehicle. If the speed of the vehicle is very high, it 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

Referenceshttp://www.seminarsonly.com/Labels/Eddy-Current-Brakes.php

http://pediain.com/seminar.html

http://en.wikipedia.org/wiki/Eddy_current_brakes

http://seminarprojects.com/Thread-eddy-current-brakes

http://seminarprojects.net/t-eddy-current-brake-full-report?page=8

http://www.seminarsonly.com/Labels/How-Eddy-Current%20Brakes-Work.php