A second approach is Electrodynamic Suspension (EDS). The difference here is that both the rail and the train are magnetised. The magnets on the train can be either electromagnets, or strong permanent magnets. The track has an array of electromagnets, and when the train is moving at speed the train and track repel each other. This system is self-correcting. The train always levitates at the optimum gap, without the need for expensive or complicated feedback systems. But the downside of EDS is that the train still needs wheels of some sort. At low speeds not enough repulsive force is generated for the train to levitate.
The system I saw at General Atomics is based on a third way, known as Inductrak, which does away with electromagnets in favour of permanent magnets arranged in a special pattern known as a Halbach array, originally designed for particle accelerators. These concentrate the magnetic field on one side, while canceling it on the opposite side. Like an EDS system, these still needs support when stationary, but levitate at much slower speeds, making them a more practical alternative for systems with multiple stops. Inductrack also has the distinct advantage that in a power failure, the cars slow down on their own, and the levitation gradually lowers as the train slows. It is also thought that over time, this approach may be more cost effective than electromagnetic systems, something that will not be known until commercial system begin to operate.
Electric surf
General Atomics has spent five years refining the power and control systems, and completing a full test programme overseen by the US Department of Transport.
“That test programme was very successful. We completed everything we can do on a test track of this type” says Dr Gurol, who now needs further funding. “The technology is ready to go to the next step. That is a demonstration system carrying either real passengers or cargo.”
But levitating is only half the equation. The trains must also move forward. The most common propulsion for Maglev trains is a linear motor. Coils of wire, mounted in the track, have a current flowing through them in sequence. They operate in a similar way to conventional rotational electric motors, except instead of being wrapped in a cylinder, they are stretched out horizontally.
The Maglev train at General Atomics, however, uses a linear synchronous motor.
“It operates similar to a wave coming towards the shore” says Dr Gurol. “That wave is not water, but electromagnetic. The surfer rides the wave.”
But in the case of the maglev, the surfer is the train, riding the electromagnetic wave.
This kind of system has several advantages over existing train technology, says Dr Gurol. “They’re better in bad weather conditions because they’re not driven by friction, and electrical contact doesn’t become an issue.”
“If you look at a typical train… they use electric motors. They need a third rail for picking up power from a guide way. They transfer that power to rotating electric motors on the vehicle, which provide the propulsive forces. That involves gearboxes, all kinds of power equipment on board, and so forth.”
As maglev trains don’t need many of these moving parts, they are subject to less wear and tear and therefore cost less to maintain, their proponents argue. But not everyone agrees, pointing out that there are too few installations to know the true cost.
Those arguments could soon be settled, however, with new systems coming online in Beijing, China and Seoul, Korea, in the coming months. And others systems are planned in Puerto Rico, Venezuela, Europe and Australia, for everything from low-speed urban transporters to high-speed transcontinental routes that could challenge plane travel. Some have even speculated that a Trans-Atlantic tunnel could use the technology. If and when that happens, I would recommend something more comfortable than a shipping container to ferry the passengers.
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