3. INTRODUCTION
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.
These brakes make use of opposing tendency of eddy currents.
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.
Contd..,
4. The Eddy Current brakes does not work by friction, there are no brake
shoe surfaces to wear out, necessitating replacement, as with friction
brakes.
Eddy current brakes are used to slow high-speed trains and roller coasters,
to stop powered tools quickly when power is turned off, and in electric
meters used by electric utilities.
5. PRINCIPLE
Faraday’s Law of Electromagnetic Induction
The induced electromotive force at any closed circuit is equal to the negative of
the time rate of change of the magnetic flux through the circuit.
Where
• E is EMF
• ΦB is Magnetic flux
• N is Number of turns of wire
E= -N dΦB/dt
6. Lenz’s Law
An induced emf always gives rise to a current whose magnetic field opposite the
change in magnetic flux.
Where
• E is EMF
• ΦB is Magnetic Flux
E= -dΦB/dt
7. TYPES
Circular:- In a circular eddy current brakes, the
conductor is a flat disk rotor that turns between the
poles of the magnet.
8. Linear :- In a linear eddy current brakes, the conductive
piece is a straight rail or track that the magnet moves along.
9. WORKING
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
Contd..,
10. generated inside the copper which would their own magnetic field.
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.
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.
11. ADVANTAGES
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
Operates at any rotational speed
Light weight
Eddy-current brakes are quite, 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 ).
12. 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
13. APPLICATIONS
For additional safety on long decants in mountain area.
For high speed passenger and goods vehicle.
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.
14. CONCLUSION
The ordinary brakes which are being used now a days stop the
vehicles by means of mechanical blocking. These may cause skidding
and wear and tear of the vehicle.
Eddy Current Brakes is a good invention for speed control of high
speed vehicles.
It is an abrasion free method for braking of vehicle including trains.
It makes use of opposite tendency of eddy currents.
