©2004 Picture Author: Mira Leung
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How it works

So what does a MagLev look like?
Picture from http://www.transrapid.de/foto_galerie/images/shanghai   A MagLev in a station; Picture from http://www.transrapid.de/foto_galerie/images/shanghai
(From afar, it looks just like your regular SkyTrain, but when you see it up close you can see that it's definitely hovering above the track.)
Look ma, no wheels! A MagLev is constantly kept afloat by electromagnets on the track (also called a guideway) and on the train's underside. As we all know, the opposing polarities of magnets are attracted to each other and the same polarities oppose each other. So a MagLev would be levitated with the track's and the train's magnets facing each other on the opposing sides. End of story, right?
Picture from www.hk-phy.org/articles/maglev/maglev_e.html

Nope, there's way more to it than you think. There are many different MagLev systems being developed. The most successful one so far is called the Transrapid system and it is currently being used by the MagLev in Shanghai. This system uses electromagnetic suspension technology (EMS) and it works on the concept that electromagnetic forces attract to a metal or another electromagnet when they face each other with the opposing polarities. Another system under development uses electrodynamic suspension technology (EDS) and it works on the concept of repulsive magnetic forces when electromagnets face each other with the same polarities. The EDS system uses superconductors cooled with liquid helium, and it's still in the experimental stage with many technical difficulties to be overcome. For starters, the train can't not be levitated at speeds less than 100 kilometres per hour and the magnetic field intensity inside the train is about 1000 times higher than that of the Transrapid System. Also, the super-cooled conductors are really expensive and the unregulated levitation causes rough rides on the train. So far, the Transrapid system is the only one commercially available. It's a more comfortable and safer system in terms of regulated levitation and the magnetic field intensity inside the passenger compartment. Its intensity is comparable to the earth's magnetic field and far below the field intensity of a hair dryer, an electric drill or a sewing machine. Since the Transrapid system has already been proven successful, it is the one we will learn about in the next couple of pages.

Briefly, in this system, the train and the track each have a set of electromagnets for levitation. The track has another set to keep the train positioned properly and to guide the train along. These guidance electromagnets keep the train from straying off track. Finally, another set of electromagnets built into the track and the train generate a electromagnetic travelling field that pushes the vehicle forward. There are two major systems in operation in a MagLev: the Levitation System and the Propulsion System .

1) The Levitation System

Support electromagnets built into the undercarriage and along the entire length of the train pull it up to the guideway electromagnets, which are called ferromagnetic reaction rails. The guidance magnets placed on each side of the train keep it centered along the track and guide the train along. All the electromagnets are controlled electronically in a precise manner. It ensures the train is always levitated at a distance of 8 to 10 mm from the guideway even when it isn't moving. This levitation system is powered by onboard batteries, which are charged up by the linear generator when the train travels. The generator consists of additional cable windings integrated in the levitation electromagnets. The induced current of the generator during driving uses the propulsion magnetic field's harmonic waves, which are due to the side effects of the grooves of the long stator so the charging up process does not consume the useful propulsion magnetic field. The train can rely on this battery power for up to one hour without an external power source. The levitation system is independent from the propulsion system.
Picture from www.visonengineer.com
2) The Propulsion System

For propulsion and braking of a MagLev, a long electromagnetic stator is installed underneath both sides of the guideway facing the train's support electromagnets, which resemble a motor's rotor. The construction of this system looks like the stator of a rotating motor was cut open and stretched along the guideway undersides and the rotor part is built into the undercarriage of a train.

The three-phase winded stator generates an electromagnetic travelling field and moves the train when it is supplied with an alternating current. The electronmagnetic field from the support electromagnets (rotor) pulls it along. The magnetic field direction and speed of the stator and the rotor are synchronized. The MagLev's speed can vary from standstill to full operating speed by simply adjusting the frequency of the alternating current. To bring the train to a full stop, the direction of the travelling field is reversed. Even during braking, there isn't any mechanical contact between the stator and the rotor. Instead of consuming energy, the Transrapid system acts as a generator, converting the breaking energy into electricity, which can be used elsewhere.

Now that we know how the Transrapid system works, let's take a look at how electromagnetism works.

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