2002
MAGLEV Magnetic Levitation The following paper was submitted and presented by me and my colleague in 2002 during our Engineering Degree Course. Maglev is a technology which uses magnetic forces to suspend vehicles in air, hence eliminating friction. This allows vehicles to achieve very high speeds which can revolutionize the ground transportation. The technology is environment friendly but is yet in development stage.
Ashutosh Agrawal Email:
[email protected] Blog: www.frontiers2explore.blogspot.com LinkedIn: www.linkedin.com/in/itsmeashu/
A : MAGLEV
NEW PROMISE
By: Ashutosh Agrawal
Anil Kumar Soni
B.Tech, final year,
B.Tech, final year,
Mechanical Engg.
Mechanical Engg.
Kamla Nehru Institute of Technology, Sultanpur
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CONTENTS 1. Abstract 2. Introduction 3. Levitation and Guidance Systems 4. Propulsion System 5. Guideway Configurations 6. Maglev Transportation 7. Maglev Launch System 8. Conclusion 9. References
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ABSTRACT Magnetic Levitation is an advanced technology known as Maglev in short. In this magnetic forces lift, propel and guide a vehicle few centimeters above a guideway using magnetic forces. The physical contact between vehicle and guideway is eliminated and permits cruising speeds in range of 500 km/h. The levitation and guidance is achieved by either magnetic attraction ( EMS - Electro Magnetic Suspension ) or repulsion ( EDS - Electro Dynamic Suspension ). The propulsion is achieved by linear motor of either ‘long stator’ or ‘short stator’. Because of its high speed, Maglev may be able to offer competitive trip-time savings in transportation. Many feasible concepts of Maglev transportation like Skytran (for intracity transportation), autoshuttle, transrapid etc have been developed and so also the various possible configurations of the guideways like ‘Y’, ‘U’, ‘T’ and Box beam. The capability of Maglev of controlled lift of thousands of pounds into the air and high acceleration has ushered it into area of space vehicle launch systems. The paper focuses on the technical aspects of Maglev that make this ‘flying in air’ phenomenon possible and its profitable applications in transportation and space launch.
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INTRODUCTION ‘Trains that fly in air’, has fascinated many, but only a few know the magnificent yet simple principle behind it. From long ago magnetic forces has been known as capable of suspending ferromagnetic particles in air. But it was at the turn of 20th century, the concept of magnetically levitated trains was first identified by two Americans, Robert Goddard and Emile Bachelet1. By the 1930’s Germany’s Hermann Kemper demonstrated the concept and in 1968 Americans James R. Powell and Gordon T. Danby were granted a patent on their design of Maglev train1. A Maglev train is levitated (i.e. lifted), guided and propelled by magnetic fields a few centimeters above the guideway, completely eliminating the physical contact between train and guideway and enabling the speed up to 500km/h1. Over the past two decades, several countries including Germany, Japan and America have conducted R&D programs in Maglev technology. Germany and Japan have invested over $1billion each to develop and demonstrate Maglev technology for High Speed Ground Transportation (HSGT) 1. Maglevs has expanded its area of application with NASA experimenting on the use of Maglev for the cheaper launches of spacecrafts.
LEVITATION AND GUIDANCE SYSTEMS As shown in the fig.[1] levitation implies vertical support and guidance implies lateral support to ensure that train does not run off the track. Same principle is employed for both support and guidance. There are two principal means of both guidance and levitation.
Attractive force system technically known as Electro Magnetic Suspension or EMS.
Repulsive force system technically known as Electro Dynamic Suspension or EDS.
Electro Magnetic Suspension: In this electromagnets are attracted to ferromagnetic rails on
the guideway.
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In the figure below the bar in blue colour is the guiderail and the one in red is electromagnet on underside of the train. Drift between the rails and levitation magnets caused by wind or when the train rounds a curve.
The gap widens between rail and track because of shortage of magnetic force.
The widening gap is sensed by gap sensors and the current is increased in leviatation magnets to increase the magnetic attraction till train comes back directly above the guide rails.
Variations in payload weight, dynamic loads and guideway irregularities are compensated for by changing the magnetic field in response to air gap measurements. Electro Dynamic Suspension: In this the magnets on the moving vehicle induce currents in
the induction coils of guideway as it passes over it. The resulting repulsive force suspends the vehicle in air. This system is inherently stable for both support and guidance because magnetic repulsion increases as the air gap decreases. However this system requires speed approx. upto 40km/h1 to levitate the vehicle. So the vehicle must be equipped with some support like wheels for speed below the 40km/h limit. This flaw as it may be seen is an advantage as it provides fail safe security in case if electrical drive systems fail. The vehicle will be still levitated at speeds above the 40km/h and will slowly touch down the rails as speed will drop. In case of EMS system if onboard electrical system were to fail fail then vehicle will touch down at very moment at high speed of 500km/h and the result can be catastrophic. The induction coils that can be used are of two types:
Simple single coil of shape ‘’.
‘8’ shaped coil. The system is called null flux system and is worth discussing.
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Null Flux System: In this system induction coils are wound as figure ‘8’. These coils are
mounted on sidewalls of guideway. If vehicle’s magnetic field passes directly through centre of the ‘8’ shaped coil, the net flux is zero. But if field is slightly below their centre, electric current is induced within the coils which then act as electromagnets temporarily. The result is a repulsive force in lower half of the coil pushing it upward and attractive force in upper half of the coil pulling it upward. Both act simultaneously to levitate the vehicle. Please refer fig.[2].
There are currently two choices of magnets used on the vehicle in EDS:
Superconducting magnets: The electrical resistivity of a superconducting material becomes zero below a certain critical temperature. The current flows in the material without any loss. So in a superconducting solenoid large current will keep circulating for long periods. A superconducting magnet require small space, less material and produce magnetic field upto 5-10 T. Eg: TcYbaCuO, critical temp:77K5.
Permanent magnets: the pemanent magnets used are that of Ne-Fe-B (Neodymium, Iron & Boron) which are arranged in Halbach array4 (invented by Klaus Halbach). Halbach array: In this permanent magnets are arranged in alternate vertical and
horizontal pattern so that the magnetic-field lines reinforce one another below the array but cancel one another above it. Refer fig.[3]. When moving, the magnets induce current in the track's circuits(‘’ shaped coil), coil), which produces an electromagnetic field that repels the array, thus levitating the train car. Halbach arrays can also provide lateral stability if they are deployed alongside the track's circuits. Refer fig.[4].
PROPULSION SYSTEM There are two alternatives for propulsion: Non-magnetic energy source: gas turbine or turboprop can be used for the propulsion but this results in a heavy vehicle and reduced operating efficiency. Magnetic energy source: It employs the principle of linear motor for the propulsion.
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A repulsive force and an attractive force induced between the magnets are used to propel the vehicle. The propulsion coils located on the sidewalls on both sides of the guideway are energized by a three-phase alternating current from a substation, creating a shifting magnetic field on the guideway. The on-board magnets are attracted and pushed by the shifting field, propelling the Maglev vehicle There are two possible cnfigurations of linear motor: Long Stator: ‘Long Stator’ propulsion uses an elctrically powered linear motor winding in
the guideway. Short Stator: In this the motor winding is on the vehicle and the guideway is passive.
Of the two the Long Stator propulsion is having high initial cost but it has high payload capacity and lower operating cost and studies indicate it to be a favoured option. The drive coils in long stator can be interspersed among the track's levitating circuits. An array of substations along the wayside sends three phase AC power, in synchronization with train motion, to the windings. The power flows in a linear sequence to generate a magnetic wave along the guideway. Only the section of the guideway under the train receives power as vehicle rides on the magnetic wave.
GUIDEWAY CONFIGURATIONS The one of the main advantages of maglev is the flexibility it offers in guideways configurations.
Box Beam: In this vehicle straddles on a concrete box beam guideway. Interaction between the vehicle magnets and laminated Aluminium ladder on each guideway sidewall generates lift and guidance. Propulsion windings are also attached to the guideway sidewalls. Fig.[5].
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U - shaped guideway: Null flux (8-shaped) levitation coils located on the sidewalls provide levitation and guidance. LSM LSM propulsion coils are also located on sidewalls.
T - shaped guideway: The vehicles wrap around this T shaped ferromagnetic guideway. Levitation and guidance are based on EMS system. The electromagnets for levitaion are located underneath the guideway and that for guidance are mounted on the edge of guideway. The guideway has LSM windings which interact with lift electromagnets mounted on vehicle. Fig.[6].
Y - shaped guideway: Here the vehicle wraps around a Y-shaped ferromagnetic guideway. The advantage is that a common set of vehicle magnets are used for levitation, guidance and proplulsion unlike in T-shaped which required two separate vehicle magnets. The pole faces of vehicle electromagnets are attracted to the underside of the ferromagnetic guideway. The guideway has LSM windings for propulsion.
MAGLEV TRANSPORTATION Due to the flexibility maglev offers many concepts of transportation which have been worked out, and the possibilities of many more are immense. We discuss here the concepts whose feasibilities have been established through extensive studies.
Maglev Trains: Maglev trains are capable of travelling at twice the speed of their fastest counterparts wheel-on-rail train TGV of France. The result is considerable trip time savings and faster trips which makes its commercialisation feasible. Various commercial maglev train projects are in progress all over the world. 1.
Maglev track connecting cities of Washington and Baltimore10.
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Maglev track between Hamburg and Berlin and between downtown Pittsburgh & the airport in Germany1 .
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34 km long Maglev track connecting Longyang Road Station on Metro Line II with Pudong International Airport in China, designed for 433 kmph speed9.
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Maglev track between Osaka and Tokyo in Japan which would reduce the trip time from bullet train’s 2 hours 30 mins to 1 hour1.
Autoshuttle6: It is a German dual-mode concept that utilizes Maglev carriers to transport a variety of conventional vehicles like cars, trucks etc. Fig.[7].
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Skytran7: Small podlike two-passenger cars would be suspended from a monorail-type track that would support the levitating circuits. The cars would be available, on call, at each station in the system. After the passengers board a car, it would glide up to the main track and merge with the traffic speeding by the station at 160 kmph. As a car approaches its destination, it would switch to an exit track, dropping down to the station to allow the passengers to disembark. Fig.[8].
MAGLEV LAUNCH SYSTEM Studies by NASA have shown that if their rockets could be accelerated up a sloping track to speeds on the order of Mach 0.8 (950 kilometers per hour) before the rocket engines were fired up, it could substantially cut the cost of launching satellites. Such a system could reduce the required rocket fuel by 30 to 40 percent, thereby making it easier for a single-stage vehicle to boost a payload into orbit4. Refer fig.[9]. NASA envisions a track a mile and a half long ( 2.4 km ) on which a winged craft would ride on a sled that would be magnetically levitated and propelled at an acceleration of 2 gs ( 19.6 m/s2 ) until it reaches a speed of 400 milesph (643.6 kmph). The contestants of this NASA project are PRT Advanced Maglev Systems, Foster-Miller and Lawrence Livermore National Lab3. PRT Advanced Maglev Systems of Park Forest built a 50 feet (15.24 m) long working model of spacecraft maglifter at Marshall Centre in Huntsville, Ala. The test vehicle weighing 30 lb reached speeds of 60 mph (96.54 kmph) in less than half a second3. Foster-Miller’s maglev launch system for NASA uses two sets of windings on the track. One set forms the stator that propels the vehicle and the other ,‘Null-Flux’, windings levitate and guide the vehicle. The experimental track built by it is 40 feet (12.2 m) long is in two parts: the first half contains the drive motor and the other comprise a magnetic brake. It was able to gain 58 mph (93 kmph) in 20 feet (6.1 m) or in three-tenth of a second3. Lawrence Livermore National Laboratory in Livermore, California is building a mag-lifter using permanent magnets arranged in Halbach array, thus avoiding use of superconductors which requires cooling at cryogenic temperatures. A 20 feet (6.1 m) long working model has been built and a larger working model is under construction at Livermore3.
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The goal of using magnetic levitation is to help to reach a target of reducing the cost of launching payload from the present $10,000 a pound to less than $1000 and perhaps eventually to $200 a pound or so3.
ADVANTAGES OF MAGLEV
Unlike trains or cars there is no surface contact or friction to slow them down. More speed = More passengers.
Faster trips :- High peak speed and high acceleration/braking enable average speed 3-4 times the national highway speed limit of 65 mph (105 kmph).
High reliability :- Less susceptible to congestion and wheather conditions than air and highway.
Petroleum independence with respect to air and auto as a result of being electrically powered.
Less polluting as a result of being electrically powered. Emissions can be controlled more effectively at the source of electric power generation than at many points of consumption, such as with air and automobile usage.
Higher capacity than air. At least 12,000 passengers with potential for even higher capacities at 3-4 minutes headways1.
High safety – both percieved and actual as based on the experiments.
Convinience and Comfort – due to high frequency frequency of service, vibration free, free, smooth-assilk train rides and quieter. At speeds below 155 mph (249.4 kmph) the noise produced by Maglev trains is less than that by conventional trains. At speeds above 155 mph, most of the noise produced by vehicle is of aerodynamic origin, wheather it is on rail or levitated1.
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CONCLUSION Any practical and commercial use of maglev has to be examined for technical & financial feasibility. The technical feasibility has been stablished by status of Japanese MLU002 prototype system currently being run in yamanshi test line5 & by German transrapid system at Emsland test facility8. Both test systems have have supplemented Maglev as the promise of a faster, smoother, clean and safer ride. The other aspect of financial feasibility is subjective to a country. To judge its financial feasibility its cost and revenue estimates have to be extensively studied in context of the geography, demography and existing transportation systems. Studies in America were carried out by National Maglev Initiative (NMI) evaluated Maglev potential and in short their conclusion was that a 300 mph ( 483 kmph ) is entirely feasible1. Various commercial projects in America, Germany, China and Japan should leave no room of doubt for its economical viability. The need to upgrade this technology for a nation can be summed up in one sentence that high mobility is linked with eonomic growth and productivity of nation. India has the most complex, widespread rail network which is now bogged down by congestion. Maglev provides the flexibility to equip existing steel tracks with magnetic levitation (based on EDS) and propulsion system. This will help in operating both maglev and conventional trains on same track. The possible incorporation of both steel track and maglev guideway is hinted in figure. By this we can replace the conventional trains with maglev trains in phased manner. The space launch systems based on maglev are also feasible as indicated by NASA. Various test models have proved its technical feasibility and cost studies by NASA clearly indicate cheaper launching in future. Over the years India has developed strong infrastructure for space exploration and has its own array of launch vehicles and a reusable vehicle ‘Avataar’ on the cards. With NASA in persuit of low cost maglev launch its time that India too must venture into this field so that it can compete, in the growing billion b illion dollar market of satellite launch, in future.
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REFERENCES 1. National Maglev Initiative (NMI), formed by DOT, DOE, USACE and others, (U.S.), ‘Final Report on the National Maglev Initiative’, www.bts.gov . 2. Leo O’ Connor, Associate Editor,’US Developers Join Magnetic Rail Push’, Mechanical Engineering, ASME, NewYork, August 1993. 3. Barbara Wolcott, ‘Induction for the Birds’, Mechanical Engineering, ASME, NewYork, Feb 2000. 4. Dr. Richard F. Post., Inventor of Inductrack Passive Magnetic Levitation, ‘Maglev: A New Approach’, Scientific American, Jan 2000. 5. Railway Technical Research Institute, Japan, ‘Maglev’, www.rtri.or.jp . 6. ‘Autoshuttle’, www.autoshuttle.de . 7. ‘Skytran’, www.skytran.net . 8. ‘Transrapid International’, www.transrapid.de . 9. ‘Shanghai Builds Maglev Rail Line’, www.goldsea.com 10. ‘Baltimore-Washington Project’, www.bwmaglev.com
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