Introduction of Eddy Current Brake Presented By :~ jayanti hazra
Contents :~ Introduction of eddy current Introduction of eddy current brake Circular eddy current brake Linear eddy current brake How eddy current brake works? Advantages Disadvantages Applications Future Aspects conclusion
INTRODUCTION Of Eddy Current Eddy currents (Foucault currents) are electric currents induced in conductors when exposed to a changing magnetic field; due to relative motion of the field source and conductor or due to variations of the field with time. This can cause a circulating flow of electrons, or current, within the body of the conductor. These circulating eddies of current have inductance and thus induce magnetic fields.
INTRODUCTION Of Eddy Current Brake Eddy current brakes, like conventional friction brakes, are responsible for slowing an object, such as rotating machinery, a moving train, or even a roller coaster There are two basic types: (1)rotational (2)linear
circular eddy current brake system Electromagnetic brakes are similar to electrical motors; non-ferromagnetic metal discs (rotors) are connected to a rotating coil, and a magnetic field between the rotor and the coil creates a resistance used to generate electricity or heat. When electromagnets are used, control of the braking action is made possible by varying the strength of the magnetic field. A braking force is possible when electric current is passed through the electromagnets. 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. The net result is to convert the motion of the rotors into heat in the rotors. Japanese Shinkansen trains had employed circular eddy current brake system on trailer cars since 100 Series Shinkansen.
LINEAR EDDY CURRENT BRAKE The principle of the linear eddy current brake has been described by the 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.
The braking energy of the vehicle is converted in eddy current losses which lead to a warming of the rail. (The regular magnetic brake, in wide use in railways, exerts its braking force by friction with the rail, which also creates heat.) The eddy current brake does not have any mechanical contact with the rail, and thus no wear, and creates no noise or odor. The eddy current brake is unusable at low speeds, but can be used at high speeds both for emergency braking and for regular braking. The first train in commercial circulation to use such a braking system has been the ICE 3. Modern roller coasters also use this type of braking, but in order to avoid the risk of potential power outages, they utilize permanent magnets instead of electromagnets , thus not requiring any power supply.
How do they work ??
Working Principle
Magnetic field lines across the magnetic material inside a copper tube
Direction of magnetic lines of force due to magnet in copper tube
Induction of Eddy current due to the motion of magnet in the copper tube
produced by induced eddy current Direction of magnetic lines of force produced by induced eddy current
(Arrangement of ECB in high speed trains)
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. It is also used in the smooth breaking and functioning of roller coasters and such fast moving machines.
FUTURE ASPECT:-~ In future ordinary brakes will 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;~ ECB is a good invention for the speed control of high speed vehicles We can control the speed of high speed vehicles without wear and tear in parts of it. Drawback of ordinary mechanical braking system can be overcome by application of ECB. It makes use of opposing tendency of eddy current.