Terry Brown
WRIT 340
12/2/11
Maglevs: Where Flying Trains come from and Where They’re Headed
Introduction
“Where is my flying car?” has become an idiomatic expression often used to decry one’s frustration with the lack of advancement of modern technology. With more and more technologies that only existed in the realm of science fiction crossing into reality, it seems puzzling that one of its main staples, the flying car, has not made the leap yet. Mankind is making progress, however; while there may be no flying car in the original sense of the term yet, flying, or rather floating trains are already in existence. Magnetic levitation (maglev for short) is a technology that has been in the works for some time, and has already been implemented in a few cases around the world. Combining some of the benefits of airplanes and trains, they offer the high capacity and easy accessibility of trains with the reduced friction of a flying body using the power of electro-magnets. Although it does have some setbacks and challenges to overcome before widespread adoption, the technology has proven itself a worthy successor to high speed rail through projects of both small and large scales.
Maglev
Though one might assume that the maglev is a brand new technology because they have only become widely adopted in recent years, its origins actually date back to the mid-19th century. The first mention of related technologies appears in a rough description of the maglev concept given by Charles Wheatstone of King’s College in the 1840’s [1]. The first related patent was issued in the US under the title “electric traction apparatus” to Alfred Zehden in 1905 [2] Zehden’s patent describes the basis of what is now known as a linear induction motor: a propulsion device that produces motion by using magnets to create a tractive force between a track and a body instead of using a rotating shaft to produce torque, as is the case in conventional motors. This is one of the core technologies used for maglev, as it allows a contactless method of propulsion for a car on a track. This patent came amid a heightened interest in electricity resulting from the widespread adoption of the light bulb and electric motor around this time; it was, however, most likely treated as a mere novelty due to its lack of a practical application. It wasn’t until Eric Laithwaite, an undergraduate at Manchester University, took interest in the subject in the 1948 that a full scale model was built [3].
The basic physics of a linear motor is easy to demonstrate: using two magnets, put them close together on a smooth surface and turn them so that they repel each other; hold one of the magnets so that it can’t move and the other will slide away [4]. Repeat this simple process and the effect can be used to propel a body forward. The basic layout of a linear motor is shown in fig (1); a body containing magnets is placed upon a “track” of electromagnets with alternating polarity. Assume that the body is in state A when the electromagnet is turned on. The current in the electromagnet is then reversed, reversing the polarity of the electromagnet. This causes the magnets in the track to repel the magnets in the body, propelling it forward, as shown in state B. The magnet then realigns itself, returning to state A a bit down the track from its beginning state. The cycle is then repeated, with the current and polarity of the electromagnet reversed so that the body is propelled further forward. Another example of this is in fig. (2), with tracks on both sides of the vehicle, instead of directly underneath it. When the alternation of the current is conducted at the right frequency, the body is continuously propelled forward. The result is a system that can move a body forward without the need for any physical contact. This is called a linear induction motor, because the system works as if a regular motor was “unrolled” onto a linear track, with the rotor placed in the body and the stators, or stationary magnets, unraveled onto the track.
Magnetic Levitation: EDS and EMS
Laithwaite, now known as the father of maglev, continued his research on the linear induction motor after becoming a professor at Imperial College of London in 1964 [3]. He worked to increase their efficiency and strength, and thus their practicality in real world applications. The next big step in the field of maglev came with Laithwaite’s development of the magnetic river in 1974: an electrodynamic suspension (EDS) magnetic levitation system, or in other words, a magnetic system that works to keep a body afloat above a track [5].
One interpretation of this is to have another set of electromagnets in the track as shown in fig. (3). In this configuration, the electromagnets in the tracks serve two purposes. The first is to act as a linear motor, similar to the function of the track shown in fig. (2). The second is to repel the train from the ground and walls, ensuring that it is stably suspended above the tracks [6].This is achieved by taking advantage of Lenz’s and Faraday’s laws: a changing magnetic field, as occurs when the magnets in the body are passing by, generates an electromotive force in the electromagnetic circuit in the tracks. While the mathematical proof for this system is beyond the scope of this article, simply put this means that if the train passes by the electromagnets in the track quickly enough, the resulting change in magnetic field will induce a current within the electromagnets. This in turn causes the track to produce a repelling magnetic force, represented by the arrows in fig. (3), which are used both to levitate the train and to keep it within the width of the track. When implemented successfully, this system makes the train “fly,” lifting it up to a few inches above the ground [5]. The advantages of EDS are that the levitation system itself does not require power, and can be integrated with the Linear motor. EDS does, however require the train to have wheels in order to accelerate to the “take off” speed required for the levitation force to become strong enough to lift the train. EDS also means that a strong magnetic field is created on-board, which can pose a threat to pace-makers and other artificial organs. There is currently no work-around for this, so trains relying on this system remain inaccessible to those with artificial hearts. An advanced form of this EDS is used in the Japanese Shinkansen Maglev (fig. 4) currently under construction, but as of yet it remains unused in any commercial system.
Meanwhile, an alternative technology to EDS was developed for Maglevs that didn’t require such strong magnetic fields. Called electromagnetic suspension (EMS), it is based on the simple idea of using active magnets in the track to support the train, as opposed to EDS where inactive magnets are induced into creating a repelling force. EMS systems commonly use permanent magnets, which don’t require power, to levitate the body. The problem with this is that placing a repelling magnet atop another magnet does not cause the top magnet to simply float above the bottom magnet; the system is unstable, meaning the top magnet will be pushed to the side, in this case causing the train to derail. To address this problem, modern EMS systems supplement the permanent magnets with computer-operated electro-magnets to keep the train in place. This system has the advantage of being able to levitate the body at lower speeds, and with smaller magnetic fields than EDS; however they require closer monitoring and constant adjustments of the electromagnets to maintain stability [7]. This system has been used in all commercial Maglev systems so far, including the German Transrapid system built by Siemens and ThyssenKrupp, recently used for the Shanghai Maglev Train shown in fig. (5) [7].
Maglev: a Promising Technology
Together, the linear propulsion motor and magnetic levitation system provide a frictionless alternative to the traditional train. Thanks to linear induction, there are no moving parts in the propulsion system, and the magnetic suspension means that maglev trains do not touch the ground. This means that the only drag experienced is aerodynamic and electromagnetic, allowing Maglevs to reach top speeds of over 360 mph with a lower energy consumption than their wheeled predecessors. A beneficial side effect of this is that the trains are quiet and stable, since the only noise and disturbances they generate come from the displacement of air.
The lack of moving parts also means that these trains need less maintenance. Since they are not in contact with the rails, there in no wear on the trains or rails. Maintenance is minimal, and the vehicles follow a maintenance schedule closer to that of aircraft than that of traditional trains, meaning that their maintenance schedules are based on hours of operation rather than distance travelled [8]. Maglevs are also immune to weather since their tracks are not subject to heat deformation or freezing, reducing traditional constraints placed on rail travel. This makes the technology ideal for any location with extreme weather.
Lastly and most importantly, linear motors allow maglevs to accellerate and deccelerate to and from high speeds in a short distance. This makes them ideal both for rapid inner-city travel since this means that they can accellerate to their top speeds even when stations are close together. Though they are not quite as fast as the average jet plane, with top speeds of 360mph as opposed to airliner’s cruising speeds of around 500mph, maglevs can also be a competitive alternative along mid-range routes because train travel does not require the security and preperation necessary to travel through an airport, reducing travel time. For routes of up to 500 miles, taking a maglev could easily become cheaper, quicker, and safer than travelling by air.
The Limitations
Despite all of these advantages of Maglevs over conventional rail, there are still many challenges that they must overcome in order to win the battle for prominence on the rails. The first is perception of safety. In the decades of testing that maglevs have gone through so far, they have encountered only a handful of accidents, which is not a bad track record. Many in the public remain wary of the technology, however, since it has had limited use in commercial operation and has yet to prove itself free of negative health effects or other threats to the public’s wellbeing. Just recently, a project intended to extend the Shanghai Maglev was shelved, partly due to concerns by the track’s neighbors over potential health problems arising from the magnetic fields [9]. Since the Shanghai Maglev uses EMS, which has weaker magnetic fields than the EDS, this is likely to be an even greater issue for EDS based technologies.
The maglev’s other weakness, and the main reason why the Shanghai Maglev extension failed, is cost. Building a track of around 50 miles can cost billions of dollars, several times more than any conventional rail technology. While in a few areas, particularly those with high ridership, Maglevs do make sense, for the majority of cases they remain impractical. To date, the only maglev systems built have been used either as experimental tracks, for airport transportation, or for exhibition purposes.
Future
As of today (Dec. 2011), there are two commercial Maglev projects that have overcome these hurdles and are currently in the works. The first is an inner-city track of about 6 miles to be built in Beijing, called the Beijing S1 line. This would become the fourth Maglev service open to the public in addition to those already in operation in China, Korea, and Japan. This is a relatively modest project with expected high speeds of 65mph and a slated completion date of 2013 [10]. It is likely that most Maglev projects in the near future will be along similar scales.
A much more ambitious project is also underway in Japan; this is the Chuo Shinkansen, or “central bullet train.” The Chuo Shinkansen is an ambitious project attempting to connect the two largest Japanese cities, Tokyo and Osaka, with an EDS Maglev train. The project has already won government approval, and construction is expected to begin in 2014. The first portion of the track is expected to open around 2027, with the full length expected to open around 2045. This long timescale results both from the cost, expected to be over $55billion, as well as the fact that a majority of the track will be built underground [11]. This would make the roughly 350 mile journey between the cities possible in as little as one hour, and would be the first large scale inter-city Maglev to be built.
There are numerous other proposals for both short and long distance Maglevs around the world, but few seem likely to begin construction in the near future primarlity due to economic concerns. It appears that the long-term success of Maglevs will depend on the success of the pioneering projects being implemented now, as well as the ability of companies to lower the cost of the technology.
Conclusion
Maglev is a technology that has been around for some time, but has only recently become feasible after years of development. Even now, its practicality is questionable due to its high costs. As shown in recent implementations and upcoming projects, however, Maglev shows great potential and is continuously improving thanks to improving technologies. Soon, with any luck it will become a much faster and more reliable alternative to conventional rail; and once mankind is able to figure out the secret to flying trains, we can only assume that the flying cars cannot be too far behind.
Bibliography
[1] K. K. Patel. (2006) “A prototype of a modular linear motor” University of South Carolina, Proquest, 2006.
[2] A. Zehden. “Electric Traction Apparatus.” US Patent 782,312. Feb 14, 1905.
[3] A. Anderson. "Dreaming of the second age of topology."New Scientist 2 Apr. 1987 pp53.
[4] BBC. "The magnetic attraction of trains" BBC News - Home., 9 Nov. 1999. [online] <
[5] E. Laithwaite. "Linear Motors for High Speed Vehicles" New Scientist 28 June 1973pp 802.
[6] L. Heim, L. Long, and N. Newcomb."Maglev Trains."Maglev Trains.University of North Carolina, [online] <
[7]Shanghai Maglev. "Maglev Technology" Shanghai Maglev Train, Shanghai Maglev Transportation Development Co., [online] <
[8] NAMTI. "Maglev Technology Explained" North American Maglev Transport Institute. North American Maglev Transport Institute, [online] <
[9] R. Chan, "Hundreds protest Shanghai maglev rail extension." Business & Financial News. Reuters, 12 Jan. 2008. [online] <
[10]J. Chen. "New maglev line to connect western Beijing" Chinadaily US Edition. Chinadaily, 19 Aug. 2011. [online] <
[11] Asahi Shinbun. "Maglev launch to be delayed to 2027." Asahi Shinbun. Asahi Shinbun, 30 Apr. 2010, [online] <