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DESIGN AND FABRICATION OF EDDY CURRENT BRAKING
SYSTEM
ABSTRACT:
This project has been motivated by the hypothesis that the torque-inertia
trade-off existing in traditional electric motors can be eliminated by use of
permanent magnets and the phenomena of eddy currents. Customer requirements
have been translated into engineering specifications consisting of maximizing
torque while minimizing rotor inertia. This specification has been further
condensed into a performance index which is maximized.
An alpha prototype has been produced in order to inform the final design
and also to perform preliminary performance calculations. From this model it was
determined that large loads will be supported and therefore a closed mechanical
structure is required. Further, elementary functional relationships between brake
performance and geometric configurations have been developed.
A final bench top eddy current brake test apparatus has been produced.
Experimentation has been performed. The current experimental results suggest
that the eddy current motor would have to be driven at high speeds to show
significant performance advantages over electric motors. This result may
however be negated by more rigorous geometric configuration experimentation
resulting in optimized eddy current brake motor configuration.
INTRODUCTION:
A linear eddy current brake in a German ICE 3 high speed train in action.
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 conductive surface moving past a stationary magnet will have circular
electric currents called eddy currents induced in it by the magnetic field, due to
Faraday’s law of induction. By Lenz’s law, the circulating currents will create
their own magnetic field which opposes the field of the magnet. Thus the moving
conductor will experience a drag force from the magnet that opposes its motion,
proportional to its velocity. The electrical energy of the eddy currents is dissipated
as heat due to the electrical resistance of the conductor.
In an electromagnetic 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.
Another advantage is that since the brake does not work by friction, there are no
brake shoe surfaces to wear out, necessitating replacement, as with friction brakes.
A disadvantage is that since the braking force is proportional to velocity the brake
has no holding force when the moving object is stationary, as is provided by static
friction in a friction brake, so in vehicles it must be supplemented by a friction
brake.
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.
LAYOUT OF EDDY CURRENT BRAKING SYSTEM:
WORKING PRINCIPLE:
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.
In an electromagnetic 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.
Another advantage is that since the brake does not work by friction, there are no
brake shoe surfaces to wear out, necessitating replacement, as with friction brakes.
A disadvantage is that since the braking force is proportional to velocity the brake
has no holding force when the moving object is stationary, as is provided by static
friction in a friction brake, so in vehicles it must be supplemented by a friction
brake.
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 quiet, frictionless, and wear-free, and require little
or no maintenance.
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 jerkfree 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.