18-08-2012, 01:31 PM
Electromagnetic breaking system
Electromagnetic breaking system.pptx (Size: 443.03 KB / Downloads: 45)
introduction
Electromagnetic brakes operate electrically, but transmit torque mechanically. This is why they used to be referred electro-mechanical brakes.
Electromagnetic brakes work in a relatively cool condition and satisfy all the energy requirements of braking at high speeds, completely without the use of friction.
All of the torque comes from the magnetic attraction and coefficient of friction between the steel of the armature and the steel of the brake field.
Braking action is made by varying the strength of the magnetic field.
If the brake was required to have an extended time to stop or slip time, a low coefficient material can be used. Conversely, if the brake was required to have a slightly higher torque (mostly for low RPM applications), a high coefficient friction material could be used.
Working principle
The working principle of the electric retarder is based
on the creation of eddy currents within a metal disc
rotating between two electromagnets.
This sets up a force opposing the rotation of the disc.
If the electromagnet is not energized, the rotation of the
disc is free and accelerates uniformly under the action of
the weight to which its shaft is connected.
When the electromagnet is energized, the rotation of the
disc is retarded and the energy absorbed appears as
heating of the disc.
If the current exciting the electromagnet is varied by a rheostat the braking torque varies in direct proportion to
Thermal dynamics
Thermal stability of the electromagnetic brakes is achieved by means of the convection and radiation of the heat energy at high temperature.
The value of the energy dissipated by the fan can be calculated by following expression
advantage
It uses electromagnetic force and not mechanical friction
Fully resettable
Can be activated at will via electrical signal
Low maintenance
Operates at any rotational speed
Light weight
disadvantage
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.
These brakes can only be used where the infrastructure has been modified to accept them.
application
It is used as a stopping mechanism in trains.
It is also used in the smooth breaking and functioning of roller coasters and such fast moving machines.