Many of 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. And if the speed of the
vehicle is very high, the brake 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
Eddy current is the swirling
current produced in a conductor, which is subjected to a change in magnetic field.
Because of the tendency of eddy currents to oppose, eddy currents cause energy
to be lost. More accurately, eddy currents transform more useful forms of energy
such as kinetic energy into heat, which is much less useful. In many applications,
the loss of useful energy is not particularly desirable. But there are some practical
applications. Such an application is the eddy current brake.
Eddy current brake works according to Faraday's law of electromagnetic induction.
According to this law, whenever 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.
Essentially the eddy current brake consists
of two parts, a stationary magnetic field system and a solid rotating part, which
include a metal disc. During braking, the metal disc is exposed to a magnetic
field from an electromagnet, generating eddy currents in the disc. The magnetic
interaction between the applied field and the eddy currents 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
CURRENT INDUCED IN A CONDUCTOR
Essentially an eddy current brake consists of two members, a stationary magnetic
field system and a solid rotary member, generally of mild steel, which is sometimes
referred to as the secondary because the eddy currents are induced in it. Two
members are separated by a short air gap, they're being no contact between the
two for the purpose of torque transmission. Consequently there is no wear as in
Stator consists of pole core, pole shoe, and field winding. The field winding
is wounded on the pole core. Pole core and pole shoes are made of east steel laminations
and fixed to the state of frames by means of screw or bolts. Copper and aluminium
is used for winding material the arrangement is shown in fig. 1. This system consists
of two parts.
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