Magnetic levitation train

From Academic Kids

Maglev can also mean general magnetic levitation.
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Shanghai_Transrapid_002.jpg
Transrapid maglev in Shanghai

A magnetic levitation train or maglev is a train-like vehicle that is suspended in the air above a single track, and propelled forward using the repulsive and attractive forces of magnetism. Because of the lack of physical contact between the track and the vehicle, the only friction is that between the carriages and the air. Consequently maglev trains can travel at very high speeds with reasonable energy consumption and noise levels (systems have been proposed that operate at up to 650 km/h (404 mph), which is far faster than is practical with conventional rail transport). Whilst the very high maximum speeds make maglev trains potential competitors to airliners on many routes, the high cost of the lines has limited their current commercial application to one line in Shanghai that takes people 30 km to the airport in just 8 minutes. Other maglev applications worldwide are being investigated for feasibility.

Contents

Technology

There are three primary types of maglev technology: One that relies on superconducting magnets (electrodynamic suspension), one that relies on feedback controlled electromagnets (electromagnetic suspension), and a newer, potentially more economical system that uses permanent magnets (Inductrack).

Japan and Germany are active in maglev research producing several different approaches and designs. In one design, the train can be levitated by the repulsive force of like poles or the attractive force of opposite poles of magnets. The train can be propelled by a linear motor on the track or on the locomotive or both. Massive electrical induction coils are placed along the track in order to produce the magnetic field necessary to propel the train, leading some to speculate that the cost of constructing such tracks would be enormous.

Unmoving magnetic bearings purely using electromagnets or permanent magnets are unstable because of Earnshaw's theorem; Diamagnetic and superconducting magnets on the other hand can support a maglev stably. Conventional maglev systems are stabilized with electromagnets that have electronic stabilization. The electromagnets and electronics tend to be large, power-hungry, and expensive.

The weight of the large electromagnet is a major design issue. A very strong magnetic field is required to levitate a massive train, so conventional maglev research uses superconductor research for an efficient electromagnet.

The effect of a powerful magnetic field on the human body is largely unknown. For the safety of the passengers, shielding might be needed, which would add additional weight to the train. The concept is simple, but the engineering and design aspects are complex.

A newer, perhaps less-expensive system is called "Inductrack." The technique has a load-carrying ability related to the speed of the vehicle, because it depends on currents induced in a passive electromagnetic array by permanent magnets. In the prototype, the permanent magnets are in a cart; horizontally to provide lift, and vertically to provide stability. The array of wire loops is in the track. The magnets and cart are unpowered, except for the speed of the cart. Inductrack was originally developed as a magnetic motor and bearing for a flywheel to store power. With only slight design changes, the bearings were unrolled into a linear track. Inductrack was developed by physicist Richard Post at Lawrence Livermore National Laboratory.

Inductrack uses Halbach arrays for stabilization. Halbach arrays are arrangements of permanent magnets that stabilize moving loops of wire without electronic stabilization. Halbach arrays were originally developed for beam guidance of particle accelerators. They also only have a magnetic field on the track side, thus reducing any potential effects on the passengers.

Currently, some space agencies, such as NASA, are researching the use of maglev systems to launch spacecraft. In order to do so, the space agency would have to get a maglev-launched spacecraft up to escape velocity, a task which would otherwise require elaborate timing of magnetic pulses (see coilgun) or a very fast, very powerful electric current (see railgun).

Maglev systems

In Berlin, the M-Bahn was built in the 1980s: a driverless maglev system with a 1.6 km track connecting 3 metro stations. Testing with passenger traffic started in August 1989, and regular operation started in July 1991. Because of traffic changes after the fall of the Berlin Wall, deconstruction of the line began only 2 months later and was completed in February 1992. The line was replaced by a regular metro line.

The world's first commercial automated system was a low-speed maglev shuttle that ran from the airport terminal of Birmingham International Airport (UK) to the nearby railway station from 1984 till 1995. The length of the track was 600 metres, and trains "flew" at an altitude of 1.5 cm. It was in operation for nearly eleven years, but obsolescence problems with the electronic systems made it unreliable in its later years and it has now been replaced with a cable-drawn system.

Transrapid (a German maglev company, which has a test track in Emsland, Germany), constructed the first operational high-speed conventional maglev railway in the world, from Shanghai, China to the new Shanghai airport in Pudong. It was inaugurated in 2002. It has a peak speed of 430 km/h (269 mph) and a track length of 30 km.

Japan has a test track in Yamanashi prefecture where test trains have reached 581 km/h (363 mph), much faster than wheeled trains. These trains use superconducting magnets which allows for a larger gap, and repulsive-type "Electro-Dynamic Suspension" (EDS). The high-speed Transrapid by comparison uses conventional electromagnets and attractive-type "Electro-Magnetic Suspension" (EMS). These "Superconducting Maglev Shinkansen", developed by the Central Japan Railway Co. ("JR Central") and Kawasaki Heavy Industries, are currently the fastest trains in the world, achieving a record speed of 581 km/h on December 2, 2003.

The world's first commercial automated "Urban Maglev" system commenced operation in March 2005 in Japan. This is the 9 station 8.9 km long Tobu-kyuryo Line Linimo, otherwise known as the Nagoya East Hill Line. The line has a minimum operating raidus of 75 m and a maximum gradient of 6%. The linear motor magnetic leviatated train has a top speed of 100 km/h. The line serves the local communcity as well as the Expo 2005 fair site. The trains are designed by the Chubu HSST Development Corp, which also operates a test track in Nagoya. Urban-type maglev trains patterned after the HSST has been constructed and demonstrated in Korea, and a Korean commercial version is proposed by Rotem.

In the US, the Federal Transit Administration (FTA) Urban Maglev Technology Demonstration program has funded the design of several low-speed urban maglev demonstration projects. It assessed HSST for the Maryland Department of Transportation and maglev technology for the Colorado Department of Transportation. The FTA also funded work to demonstrate new maglev designs by General Atomics at California University of Pennsylvania, of the MagneMotion M3, and of the Maglev2000 of Florida superconducting EDS system. Other US urban maglev demonstration projects of note are the LEVX in Washington State, the Massachusetts-based Magplane, and a design similar to HSST by American Maglev Technology of Florida at Old Dominion University in Virginia.

UniModal is a proposed personal rapid transit system using Inductrack suspension to achieve average commute speeds of 160 km/h (100 mph) in the city.

On December 31, 2000, the first manned high-temperature superconducting maglev was successfully tested in Southwest Jiaotong University, Chengdu, China. This system is based on the principle that bulk high-temperature superconductors can be levitated or suspended stably above or below a permanent magnet. The load is over 530 kg and the levitation gap is over 20 mm. The system uses liquid nitrogen, which is very cheap, to cool the superconductor.

The first patent for a magnetic levitation train propelled by linear motors was US patent 3,470,828, issued in October 1969 to James R. Powell and Gordon T. Danby. The technology underlying it was invented by Eric Laithwaite, and described by him in "Proceedings of the Institution of Electrical Engineers", vol. 112, 1965, pp. 2361-2375, under the title "Electromagnetic Levitation". Laithwaite patented the linear motor in 1948.

See also

External links

de:Maglev eo:Maglevo fr:Train sustentation magntique id:Kereta maglev ja:浮上式高速鉄道 nl:Magneetzweeftrein pl:Kolej magnetyczna ru:Маглев sl:Maglev zh-cn:磁悬浮列车 zh-tw:磁懸浮列車

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