A SEMINAR REPORT ONEDDY CURRENT BRAKING SYSTEM & CHARACTERISTIC ANALYSIS USING THE LINEAR HALBACH ARRAY 1|P ag e Introduction 1. 6 Advantage 7 Conclusion 8 Bibilography. 4.1 General Characterstics.2 Linear Eddy Current Brake.1.1 Circular Eddy Current Brake.1 characteristic analysis of eddy-current brake system using the linear halbach array 5. Installation Location. 2|P ag e .CONTENTS Abstract 1. 5. 5. 5. Characteristics of Eddy current Brakes.2 Thermal Dynamics. Electrical Controls system. Working principle. 3. 2. 1. eddy current brakes slow an object by creating eddy currents through electromagnetic induction which create resistance. For such a breaker. Unlike the friction brakes. forces according to the secondary relative permeability. we give analytical formulas considering end effects for its magnetic field. and in turn either heat or electricity. such as a train or a roller coaster etc. linear Halbach magnetized mover is applied to eddy current braking system for high speed. eddy current distribution. In this paper. which apply pressure on two separate objects. is responsible for slowing an object. 3|P ag e .The results given here are purely analytic.ABSTRACT This paper presentation explores the working principle of eddy current brake mechanism. like a conventional friction brake. and conductivity. An eddy current brake. which can be analysed by Maxwell 3D Transient solver. 1 CIRCULAR EDDY CURRENT BRAKE: Electromagnetic brakes are similar to electrical motors. the current swirls in such a way as to create a magnetic field opposing the change. nonferromagnetic metal discs (rotors) are connected to a rotating coil. During braking. such as kinetic energy. The magnetic interaction between the applied field and the eddy currents acts to slow the wheels down. into heat. to do this in a conductor. eddy currents transform more useful forms of energy. producing a smooth stopping motion.1. In many applications the loss of useful energy is not particularly desirable. The faster the wheels are spinning. eddy currents cause energy to be lost. but there are some practical applications. (2) Linear eddy current brake 1. There are two basics types of Eddy current brake as follows(1) Circular eddy current brake. electrons swirl in a plane perpendicular to the magnetic field. When electromagnets are used. One is in the brakes of some trains. control of the 4|P ag e . More accurately. generating eddy currents in the wheels. and a magnetic field between the rotor and the coil creates a resistance used to generate electricity or heat. meaning that as the train slows the braking force is reduced. which is generally much less useful. By Lenz's law. Because of the tendency of eddy currents to oppose.INTRODUCTION An eddy current is a swirling current set up in a conductor in response to a hanging magnetic field. the metal wheels are exposed to a magnetic field from an electromagnet. the stronger the effect. This magnet does not touch the rail. These disturb the magnetic field in such a way that the magnetic force is diverted to the opposite of the direction of the movement. but is held at a constant small distance from the rail (approximately seven millimeters). However.INSTALLATION LOCATION 5|P ag e . thus creating a horizontal force component.braking action is made possible by varying the strength of the magnetic field. which then resists the rotation of the discs. 1. exerting only a vertical pull on the rail. A braking force is possible when electric current is passed through the electromagnets. which are being magnetized alternating as south and north magnetic poles. and causes eddy currents. It does not move along the rail. providing braking force. Japanese Shinkansen trains had employed circular eddy current brake system on trailer cars since 100 Series Shinkansen. When the magnet is moved along the rail. N700 Series Shinkansen abandoned eddy current brakes in favour of regenerative brakes since 14 of the 16 cars in the trainset used electric motors. hence in French the eddy current brake is called the "frein à courants de Foucault". as with the magnetic brake. it generates a nonstationary magnetic field in the head of the rail. which works against the movement of the magnet. The linear eddy current brake consists of a magnetic yoke with electrical coils positioned along the rail.2 LINEAR EDDY CURRENT BRAKE: The principle of the linear eddy current brake has been described by the French physicist Foucault. 2. 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. The net result is to convert the motion of the rotors into heat in the rotors. which then generates electrical tension (Faraday's induction law). Any air flow movement within the chassis of the vehicle is found to have a relatively insignificant effect on the air flow around tire areas and hence on the temperature of both front and rear discs. the braking torque varies in direct proportion to the value of the current. Due to its specific installation location (transmission line of rigid vehicles). 6|P ag e . Typically. So the application of the retarder does not affect the temperature of the regular brakes. completely without the use of friction. 3. When the electromagnet is energized. It was the Frenchman Raoul Sarazin who made the first vehicle application of eddy current brakes. The development of this invention began when the French company Telma. the retarders help to extend the life span of the regular brakes and keep the regular brakes cool for emergency situation. The practical location of the retarder within the vehicle prevents the direct impingement of air on the retarder caused by the motion of the vehicle. If the current exciting the electromagnet is varied by a rheostat. the rotation of the disc is free and accelerates uniformly under the action of the weight to which its shaft is connected.Electromagnetic brakes work in a relatively cool condition and satisfy all the energy requirements of braking at high speeds. The brake is fitted into the chassis of the vehicle by means of anti-vibration mounting. The propeller shaft is divided and fitted with a sliding universal joint and is connected to the coupling flange on the brake. electromagnetic brakes have been mounted in the transmission line of vehicles. If the electromagnet is not energized. In that way. which sets up a force opposing the rotation of the disc. the rotation of the disc is retarded and the energy absorbed appears as heating of the disc.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. electromagnetic brakes have better heat dissipation capability to avoid problems that friction brakes face. (3) A multiple domain eddy current regions are needed including master/slave boundaries. permit independent cooling of the arrangement. The stator assembly is 9 supported resiliently through anti-vibration mountings on the chassis frame of the vehicle. which are integral to the disc. Careful design of the fins. 7|P ag e . which provide the braking force when subject to the electromagnetic influence when the coils are excited. A typical retarder consists of stator and rotor. The stator holds 16 induction coils. The coils are made up of varnished aluminum wire mounded in epoxy resin.associated with Raoul Sarazin. The rotor is made up of two discs. energized separately in groups of four. (2) A fine mesh is required due to very small skin depths.1 Block diagram of Eddy current Brake The simulation eddy current brakes is difficult because. developed and marketed several generations of electric brakes based on the functioning principles described above (Reverdin. (1)Physical effects such as nonlinear saturation. skin effects and motion induced eddy currents must be considered simultaneously. 1974). Fig 1. A transient solution with time-stepping is necessary. The excitation can be DC. It uses both linear and nonlinear materials. and transient voltages or currents. An external schematic circuit is available and considers skin and proximity effects.The results from three unique simulations will be shown while pointing out the challenges of each design and the methodology needed to allow the simulation to be successful Collaborative.Solves transient magnetic fields caused by time-varying or moving electrical sources and permanent magnets. Fig 1. It also considers motioninduced eddy currents and time-diffusion of magnetic field. sinusoidal.Which is well suited for magnetic problems with motion. They can be analysed by Maxwell 3D Transient solver .2(a) 8|P ag e . and the four remaining positions increase the braking power in sequence.Fig: 1.ELECTRIC CONTROL SYSTEM The energization of the retarder is operated by a hand control mounted on the steering column of the vehicle. and rotor use the same non linear iron. In this case. 4.2(c) Fig 1.model set up for eddy current brake simulation by using Maxwell 3-D transient solver The Red coils are fed by a continuous DC current. This control has five positions: the first is ‘off’.(b).2 (b) Fig : 1. the contacts are switched on successively over the slack movement of the brake pedal. The rotation of the light blue rotor. The use of an automatic control must be coupled with a cut-off system operating at very low vehicle speed in order to prevent energization of the retarder while the vehicle is stationary with the driver maintaining pressure on the brake pedal.2 (a).(c).Poles. produces FOUCAULT’scurrents that brake the device. blooming. that creates a permanent magnetic field. which in turn close the four groups of coil 9|P ag e . This hand-control system can be replaced by an automatic type that can operate mechanically through the brake pedal. Both the manual control and the automatic control activate four solenoid contractors in the relay box. as do exhaust and hydrokinetic brakes.circuits within the electric brake at either 24 volts or 12 volts. and the potentially “brake fade” problem could be avoided. 10 | P a g e . In research conducted by a truck manufacturer. These performance of electromagnetic brakes make them much more competitive candidate for alternative retardation equipments compared with other retarders. as appropriate (Reverdin 1974 and Omega Technologies). It does not need a subsidiary cooling system. The installation of an electromagnetic brake is not very difficult if there is enough space between the gearbox and the rear axle. The exhaust brake is an on/off device and hydrokinetic brakes have very complex control system.CHARACTERISTIC OF ELECTROMAGNETIC BRAKES 5. it is apparent that the electromagnetic brake is an attractive complement to the safe braking of heavy vehicles. and at least three times the braking power of an exhaust brake (Reverdin 1974). The electromagnetic brake also has better controllability. The brake linings would last considerably longer before requiring maintenance. The electromagnetic brake control system is an electric switching system which gives it superior controllability. the electromagnetic brake prevents the dangers that can arise from the prolonged use of brakes beyond their capability to dissipate heat. and therefore practically never reach high temperatures. From the foregoing. It does not rely on the efficiency of engine components for its use. Furthermore. the friction brakes can be used less frequently. This is most likely to occur while a vehicle descending a long gradient at high speed.1 GENARAL CHARACTERSTICS: It was found that electromagnetic brakes can develop a negative power which represents nearly twice the maximum power output of a typical engine. By using the electromagnetic brake as supplementary 10 retardation equipment. it was proved that the electromagnetic brake assumed 80 percent of the duty which would otherwise have been demanded of the regular service brake (Reverdin 1974). 5. furthermore. and these "onesided flux" structures were initially described by him as a "curiosity". a physicist at Lawrence Berkeley National Laboratory. An eddy current braking system of high speed railway is developed because of the adhesion limit. As a result. In the 1980s. the magnetic field is enhanced on the bottom side and cancelled on the top side The effect was discovered by Mallinson in 1973.1. the braking system with a linear Halbach magnetized mover develops a higher braking force because of the strong flux density [2]For high-speed linear braking system. In the diagram. the late Klaus Halbach. invented the Halbach array to focus accelerator particle beams. although he recognised at the time the potential for significant improvements in magnetic tape technology. Linear eddy current braking system are used in magnetic train to avoid the abrasion of mechanical disc brake [1] The eddy-cur-levitation applications and in high-speed vehicles in order to rent braking system with dc-excited magnet inherently needs the power supply and has the consequent power losses. dynamic end effects are caused by the relative motion between the mover of a finite length and an infinitely long secondary. the end effect should be necessarily accounted for . 11 | P a g e . If the dc-excited magnetic poles are replaced with permanent magnet.5.a braking system has a high efficiency due to no power losses and a high power/weight ratio. In particular. a magnetic drag force occur [3]In the characteristic analysis of linear braking system with magnet for high speed. the attraction force decreases notably with speed and.1 CHARACTERISTIC ANALYSIS OF EDDY-CURRENT BRAKE SYSTEM USING THE LINEAR HALBACH ARRAY: HALBACH ARRAY A Halbach array is a special arrangement of permanent magnets that augments the magnetic field on one side of the array while cancelling the field to near zero on the other side. 2(a) fig 2.A. 2.2(a) Magnetostatic field distribution in the transverse direction. MODEL AND ASSUMPTIONS In order to obtain an analytical solution of the eddy-current braking system with a linear Halbach array mover shown in Fig. Fig 2. fig 2. 2. Fig 2. B.) 2) The induced currents in the secondary vary sinusoidally along the transverse direction. 2.2(b).1 Schematic of eddy current braking system.1.1 Fig 2. 2 Eddy-current braking system using linear Halbach array. FIELD EQUATIONS: 12 | P a g e . as shown in Fig. 1) The flux density distribution in the air gap is symmetric to the center of the secondary in the transverse direction(direction as shown in Fig. the following assumptions are made.)and sinusoidal in the longitudinal direction ( direction.2(a). Fig 2.2(b) Fig.2 (b) Magnetostatic field distribution in the longitudinal direction. C.According to the above assumptions. υ is the relative mover speed. These phenomena are called “end effect.in fig 3 shows the magnetostatic field distribution due to magnet source Fig 3 : Magnetostatic field distribution due to magnet source.SIMULATION RESULTS ACCORDING TO THE SECONDARY PERMEABILITY AND CONDUCTIVITY: Using three-dimensional (3-D) finite-element analysis. the air-gap reaction field fulfils the equations Where σ is the electric conductivity of the secondary. For a fixed value of the secondary conductivity and permeability. the drag and attraction force variation with speed is calculated and ploted in fig 4(c) 13 | P a g e . for the speed is high. respectively. Fig. the eddy current density increases and the air-gap flux density has a nonuniform distribution. 4(a) and fig 4(b) shows how the transverse eddy-current density and absolute value of air-gap flux density longitudinal distributions vary for two different speeds. and d is the field penetration depth.” For a fixed low value of the secondary conductivity. The solution of (3) takes the forms. It can be seen that. the curie temperature of the disc material could never been reached(Reverdin 1974). 14 | P a g e . Therefore. (a) Distributions of the eddy current density in the transverse direction and (b) flux density in the longitudinal direction 5. The major part of the heat energy is imparted to the ventilationg air which is circulating vigorously through the fan of the heated disc. 4. The electromagnetic brakes has excellent heat dissipation efficiency owing to the high temperature of the surface of the disc which is being cooled and also because the flow of air through the centrifugal fan is very rapid.2 THERMAL DYNAMICS Thermal stability of the electromagnetic brakes is achieved by means of the convection and radiation of the heat energy at high temperature.Fig 4 (a) Fig 4 (b) Fig. The practical location of the electromagnetic brakes prevents the direct impingement of air on the brakes caused by the motion of the vehicle. Low maintainance cost.ADVANTAGE Advantage Of Eddy Current Brake are as follows: 1. These are non mechanical. Operates at any rotational speed. Fully resettable. electromagnetic brakes have better thermal dynamic performance than regular friction brakes. Any air flow movement within the chassis of the vehicle is found to have a relatively 12 insignificant effect on the air flow and hence temperature of both front and rear discs. 3. Can be activated at will via electrical signal. Due to its special mounting location and heat dissipation mechanism.no parts need to be replaced. 2. 5. 15 | P a g e . 4. 6.no moving parts hence no friction. and forces according to the secondary relative permeability and conductivity were presented. eddy current distribution. Comparisons between numerical simulations and experimental data were also presented. Based on analytical 2-D field solutions considering dynamic end effect. A Halbach magnetized mover was applied to a high-speed eddy current braking system. It was observed that the air-gap flux density has a nonuniform distribution for the high speed. they have been widely used on heavy vehicles where the ‘brake fading’ problem is serious. 16 | P a g e . the magnetic field. The same concept is being developed for application on lighter vehicles. CONCLUSION With all the advantages of electromagnetic brakes over friction brakes.7. eddycurrentprojects. no. IEEE. and SangSub Jeong IEEE transactions on magnetics. Sung-Ho Lee.org 4. Characteristic Analysis of Eddy-Current Brake System Using the Linear Halbach Array -Seok-Myeong Jang.com 3.Bibilography 1. 5. Member. september 2002 2.wikipedia. “Analysis of Eddy Current Brakes using Maxwell 3D Transient” -Valeo Telma Electrical System. 38. www. vol. 17 | P a g e . www.