MagLev –Magnetic LeviationDriving without wheels, Flying without wingsBY – Debasis Ray, BS-10-224
Magnetic Leviation Magnetic levitation is the use of magnetic fields to levitate a(usually) metallic object. Manipulating magnetic fields and controlling their forces canlevitate an object. Using either Ferromagnetism or Diamagnetisim object can beleviated. A superconductor is perfectly diamagnetic and electromagnetscan exhibit varying levels of ferromagnetism Most imoportant application of Magnetic Leviation isTransrapid magnetic lift trains.
Basic Principle of Maglev TrainsMaglev trains have to perform the following functions tooperate in high speeds1.Leviation2.Propulsion3.Lateral Guidance
Types of Maglev TrainsBased on the technique used for Leviation the are two types ofMaglev trains1. Electromagnetic Suspension -Attractive2. Electrodynamic Suspension -repulsive
Electromagnetic Suspension(EMS) Electromagnetic Suspension uses electromagnets to leviatethe train
Principle of Magnetic Leviation In the EMS-attractive system, the electromagnets which dothe work of levitation are attached on the top side of a casingthat extends below and then curves back up to the rail that isin the center of the track.
The rail, which is in the shape of an inverted T, is aferromagnetic rail. When a current is passed through it, and theelectromagnet switched on, there is attraction, and thelevitation electromagnets, which are below the rail, raiseup to meet the rail. The car levitates.
Principle of Propulsion A linear electric motor (LEM) is a mechanism which converts electricalenergy directly into linear motion without employing any intervening rotarycomponents Linear Induction Motor (LIM) is basically a rotating squirrel cage inductionmotor opened out flat Instead of producing rotary torque from a cylindrical machine it produceslinear force from a flat one. LIM thrusts vary from just a few to thousands of Newtons , dependingmainly on the size and rating Speeds vary from zero to many meters per second and are determined bydesign and supply frequency
Gap Sensor The attractive force is controlled by a gap sensor that measures thedistance between the rails and electromagnets.
Principle of Lateral Guidance The levitation magnets and rail are bothU shaped(with rail being an inverted U). The mouths of U face one another. This configuration ensures that when ever a levitational forceis exerted, a lateral guidance force occurs as well. If the electromagnet starts to shift laterally from the center ofthe rail, the lateral guidance force is exerted in proportion tothe extent of the shift, bringing the electromagnet back intoalignment.
Superconductivity Superconductivity occurs in certain materials at very lowtemperatures. When superconductive, a material has an electrical resistanceof exactly zero. It is also characterized by a phenomenon called the Miessnereffect. This is the ejection of any sufficiently weak magneticfield from the interior of the superconductor as it transitionsinto the superconducting state.
•The passing of the superconducting magnets by figure eightlevitation coils on the side of the tract induces a current in thecoils and creates a magnetic field. This pushes the train upwardso that it can levitate 10 cm above the track.•The train does not levitate until it reaches 50 mph, so it isequipped with retractable wheels.PRINCIPLE OF MAGNETLEVITATION
•The propulsion coils located on the sidewalls on both sides of theguideway are energized by a three-phase alternating current froma substation, creating a shifting magnetic field on the guideway.•The on-board superconducting magnets are attracted and pushedby the shifting field, propelling the Maglev vehicle.•Braking is accomplished by sending an alternating current in thereverse direction so that it is slowed by attractive and repulsiveforces.PRINCIPLE OF PROPULSION
•When one side of the train nears the side of the guideway, thesuper conducting magnet on the train induces a repulsive forcefrom the levitation coils on the side closer to the train and anattractive force from the coils on the farther side.•This keeps the train in the center.PRINCIPLE OF LATERALGUIDANCE
The SCM (Super Conducting Magnet) Each SCM contains 4 SC coils. The SCM features highreliability and high durability. The cylindrical unit at the top is a tank holding liquefied heliumand nitrogen. The bottom unit is an SC coil alternately generating N polesand S poles.
An EDS system can provide both levitation and propulsionusing an onboard linear motor. EMS systems can only levitate the train using the magnetsonboard, not propel it forward.
Pros and Cons of Different TechnologiesTECHNOLOGY PROS CONSEMS(Electromagneticsuspension)Magnetic fields inside andoutside the vehicle are lessthan EDS; proven,commercially availabletechnology that can attainvery high speeds(500 km/h); no wheels orsecondary propulsionsystem neededThe separation betweenthe vehicle and theguideway must beconstantly monitored andcorrected by computersystems to avoid collisiondue to the unstable natureof electromagneticattraction; due to thesystems inherent instabilityand the required constantcorrections by outsidesystems, vibration issuesmay occur.
TECHNOLOGY PROS CONSEDS(Electrodynamicsuspension)Onboard magnets andlarge margin between railand train enable highestrecorded train speeds(581 km/h) and heavy loadcapacity; has recentlydemonstrated (December2005) successfuloperations using hightemperaturesuperconductors in itsonboard magnets, cooledwith inexpensive liquidnitrogenStrong magnetic fieldsonboard the train wouldmake the train inaccessibleto passengers withpacemakers or magneticdata storage media such ashard drives and creditcards, necessitating theuse of magnetic shielding;limitations on guidewayinductivity limit themaximum speed of thevehicle; vehicle must bewheeled for travel at lowspeeds.
Advantages of MagneticLevitated Transportation System Maglev uses 30% less energy than a high-speed train traveling atthe same speed (1/3 more power for the same amount of energy). The operating costs of a maglev system are approximately halfthat of conventional long-distance railroads. Research has shown that the maglev is about 20 times safer thanairplanes, 250 times safer than conventional railroads, and 700times safer than automobile travel. Maglev vehicle carries no fuel to increase fire hazard The materials used to construct maglev vehicles are non-combustible, poor penetration transmitters of heat, and able towithstand fire.
Current Projects Currently operational systems include Transrapid (Germany )and High Speed Surface Transport (Japan ). There areseveral other projects under scrutiny such as the SwissMetro, Seraphim and Inductrack. All have to do with personalrapid transit Germany and Japan have been the pioneering countries inMaglev research
Other Applications NASA plans to use magnetic levitation for launching of spacevehicles into low earth orbit. Boeing is pursuing research in MagLev to provide aHypersonic Ground Test Facility for the Air Force. The mining industry will also benefit from MagLev. There are probably many more undiscovered applications!
Conclusion The MagLev Train: Research on this ‘dream train has beengoing on for the last 30 odd years in various parts of the world. The chief advantages of this type of train are:Non-contact and non-wearing propulsion, independent offriction, no mechanical components like wheel, axle. Maintenance costs decrease The MagLev offers a cheap, efficient alternative to the currentrail system. A country like India could benefit very much if thiswere implemented here. Further possible applications need tobe explored.