19-06-2012, 06:06 PM
Magnetic levitation transport
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Magnetic levitation transport is a form of transportation that suspends guides and propels vehicles via electromagnetic force. This method can be faster than wheeled mass transit systems, potentially reaching velocities comparable to turboprop and jet aircraft (500 to 581 km/h).
The only notable currently operating commercial application of a high-speed maglev line is the IOS (initial operating segment) demonstration line of Shanghai, China that transports people 30km (18.6 miles) to the airport in just 7 minutes 20 seconds (top speed of 431 km/h or 268 mph, average speed 250 km/h or 150 mph). Other maglev projects worldwide are being studied for feasibility. However, scientific, economic and political barriers and limitations have hindered the widespread adoption of the technology.
All operational implementations of maglev technology have had minimal overlap with wheeled train technology and have not been compatible with conventional railroad tracks. Because they cannot share existing infrastructure, maglev must be designed as complete transportation systems. The term "maglev" refers not only to the vehicles, but to the railway system as well, specifically designed for magnetic levitation and propulsion.
Magnetically Levitated Trains
The principal of a Magnet train is that floats on a magnetic field and is propelled by a linear induction motor. They follow guidance tracks with magnets. These trains are often referred to as Magnetically Levitated a train which is abbreviated to Maglev. Although maglev don't use steel wheel on steel rail usually associated with trains, the dictionary definition of a train is a long line of vehicles traveling in the same direction - it is a train.
A super high-speed transport system with a non-adhesive drive system that is independent of wheel-and-rail frictional forces has been a long-standing dream of railway engineers. Maglev, a combination of superconducting magnets and linear motor technology, realizes super high-speed running, safety, reliability, low environmental impact and minimum maintenance.
Technology of Maglev
There are two primary types of maglev technology:
• Electromagnetic suspension (EMS) uses the attractive magnetic force of a magnet beneath a rail to lift the train up.
• Electrodynamics suspension (EDS) uses a repulsive force between two magnetic
fields to push the train away from the rail.
Electromagnetic suspension
In current EMS systems, the train levitates above a steel rail while electromagnets, attached to the train, are oriented toward the rail from below. The electromagnets use feedback control to maintain a train at a constant distance from the track.
Propulsion
An EMS system can provide both levitation and propulsion using an onboard linear motor. EDS systems can only levitate the train using the magnets onboard, not propel it forward. As such, vehicles need some other technology for propulsion. A linear motor (propulsion coils) mounted in the track is one solution. Over long distances where the cost of propulsion coils could be prohibitive, a propeller or jet engine could be used.
Stability
Static magnetic bearings using only electromagnets and per magnets are unstable, as explained by Earns haw’s theorem. EMS systems rely on active electronic stabilization. Such systems constantly measure the bearing distance and adjust the electromagnet current accordingly. As all EDS systems are moving systems (i.e. no EDS system can levitate the train unless it is in motion), Earns haw’s theorem does not apply to them.