Eddy current braking

EDDY CURRENT BREAKING

PRESENTED BYSACHIN PRAKASH

U10EE084ELECTRICAL DEPARTMENT

CONTENTS

• Introduction• Theory Of Operation• Working Principle• Constructional Details• Classification of eddy current brakes• Advantages & Disadvantages• Applications• Conclusion

What is Induction?– “The induced electromotive force in any closed circuit is equal to

the negative of the time rate of change of the magnetic flux through the circuit.”

• Lenz’s Law– Why circuits obey Newton’s third law along with the

conservation of energy – “An induced electromotive force (emf) always gives rise to a

current whose magnetic field opposes the original change in magnetic flux”

Eddy Current Brakes

• It slow an object by creating eddy currents through emi which create resistance, and in turn either heat or electricity.

• Braking action is made by varying the strength of the magnetic field.

• A braking force is possible when electric current is passed through the electromagnets.

Induction Currents = Eddy Currents

• Called “Eddy” since they are analogous to fluid eddies in formation and behavior

• Responsible for the opposing magnetic fields that produce drag and heating effects

• The drag effects give rise to induction braking– Absent external potentials will result in the system coming to a

halt• Heating effects are exploited by devices such as induction

cookers– If left unchecked, then it could result in serious damage to

mechanical/circuit components

Check on Heat Effects

• High voltage circuits are constructed as a series of “laminations” to reduce eddy currents

• Solid conductors would suffer increased resistivity and large energy losses (heat)

Drag Effects: Magnetic Braking

• Not to be confused with stellar magnetic braking– The primary reason for slow stellar rotations

• Utilized in many practical applications:– Trains (Maglev and conventional) as a braking system– Some roller coasters– Braking Industrial equipment and power tools– Some exercise equipment

• Rowing or Spin machines… to increase resistance– Determining structural defects in conductive materials– Metal Detectors

THEORY OF OPERATION

• 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

The stator comprises steel pole pieces with hollow cores that establish a magnetic circuit for a magnetic flux field.

The pole pieces have machine-wound electrical windings.

The windings are fastened with pole caps.

The hollow core reduces the weight and material of the stator without significantly adversely affecting the braking capacity.

The pole caps reduce the magnetic saturation and increases the overall brake torque output.

HOW DO THEY WORK ??

Working Principle

• 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

Magnetic field lines across the magnetic material inside a copper

tube

Direction of magnetic lines of force due to magnet in copper tube

DIRECTION OF MAGNETIC LINES OF FORCE

PRODUCED BY INDUCED EDDY CURRENT

ARRANGEMENT OF DIFFERENT PARTS IN EDDY CURRENT BRAKE

Types of Eddy current brake

• Circular eddy current brake• Linear eddy current brake

CIRCULAR EDDY CURRENT BRAKING SYSTEM

non-ferromagnetic metal discs (rotors) are connected to a rotating coil, and a magnetic field between the rotor and the coil creates a current used to generate electricity which produces heat.

When electromagnets are used, control of the braking action is made possible by varying the strength of the magnetic field.

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 (Lenz's law), which then resists the rotation of the discs, providing braking force which decelerate the moving system.

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

Circular eddy current brakes

Linear eddy current brakes

It is first described by French physicist Foucault.

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, as with the magnetic brake, but is held at a constant small distance from the rail (approximately seven mm).

When the magnet is moved along the rail, it generates a non-stationary magnetic field in the head of the rail, which then generates electrical tension (Faraday's induction law), 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, thus creating a horizontal force component, which works against the movement of the magnet.

Linear Eddy Current Brake

Advantages. . .

Independent of wheel/rail adhesion. No contact, therefore no wear or tear. No noise or smell. Adjustable brake force. High brake forces at high speeds. Used also as service brake. It uses electromagnetic force and not friction Non-mechanical (no moving parts, no friction) Can be activated at will via electrical signal Low maintenance Light weight

DISADVANTAGES:-~

Braking force diminishes as speed diminishes with no ability to hold the load in position at standstill.It can not be used at low speed vehicles or vehicle running at low speed.ECB is used with ordinary mechanical brakes.Nowdays ECB is using only for safety purpose.

Applications

It is used as a stopping mechanism in trains. Ex- Japanese Shinkansen trains

It is also used in the smooth breaking and functioning of roller coasters and such fast moving machines. Ex-Intamin roller coaster in Netherlands.

To eliminate vibration from spacecraft.

Future Aspects

In future ordinary brakes can 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.

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

THANK YOU