|End of Page||Exploring Space ...||Site Map||Overview Page|
Maglev technology began to be worked on, in a serious way, during the 1970s. The most advanced work is largely done in Germany and Japan. During the last decade, America has completed some impressive concept design work, but is hampered by the lack of a test track.
However, the first conception of maglev traces to the early part of this century.
Magnetism has been known since antiquity. Electromagnetism (in which a soft-iron core material is magnetized by passing a current through a coil which is wound around the core) has been studied at least for 150 years. In 1904, the famed American rocket scientist Robert Goddard, while still a college freshman, made the first known breakthrough conceptualizing maglev. In a paper, he proposed a frictionless form of travel by raising train cars off the rails by electromagnetic repulsion roadbeds. The trains would travel at fantastic speeds inside a steel vacuum tube. In 1910, French engineer Emile Bachelet applied for a patent on a rail car which for purposes of levitation would use alternating-current electromagnets, and for purposes of propulsion would use solenoids at intervals along a road-bed. In 1935, German engineer Hermann Klemper demonstrated that levitation must be achievable with economical power output.
But it was in 1972, that the Germans conceived and began pursuing an experimental maglev vehicle, called Transrapid 02, on the basis of the electromagnetic (attractive) system. By 1979, visitors to Germany's Transportation Exposition in Hamburg could ride on a 36 ton Transrapid maglev train over a very short half- mile test track. Progress continued. By 1988, on a 6 mile straight test track in Lathen, Germany, the Transrapid 06 achieved a speed of 250 miles per hour. Much testing has been done. The latest version of the Transrapid, the TR07, has accumulated over 60,000 miles in operational experience at its 19 mile long, bone-shaped, test track in Emsland, Germany. It is by far, the most tested maglev system in the world.
Meanwhile, the Japanese concentrated primarily on electrodynamic (repulsion) system. This system has a much larger gap between the rail and the maglev vehicle than the German electromagnetic EMS system, up to 7 inches versus 3/8 of an inch, respectively. The Japanese said that the EMS-attractive system gap was too narrow to account for the hilly terrain of Japan, and Japan's occasional earthquakes. As early as December, 1979, Japan's Railway System, which runs its EDS maglev system, ran an unmanned experimental vehicle using this system at a record speed of 310 miles per hour. Successor vehicles, which have concentrated on developing the stability of the vehicles, have geared down the travelling speeds, but have achieved higher accelerations, achieving 7.9 feet/sec2.
The German Transrapid has announced that is prepared to begin construction on a commercial maglev system between Hamburg and Berlin, Germany.
Some would say that maglev is the biggest breakthrough in ground transportation since the invention of the wheel. Ironically, this distinction was achieved precisely by eliminating wheel-on- rail, or wheel-on-roadway modes of transport. Without friction, without moving parts which have to be lubricated and tended to, the operational side of vehicle maintenance is greatly reduced.
But what exactly does it mean to travel without a wheel? For example, what then drives the maglev, since the normal tractive power of a locomotive, a car engine, or the horse that pulls the wagon is now eliminated. Without the normal tractive power, what makes maglev go?
Most children who have played with magnets, which should include everyone, have noticed that north pole attracts south pole. If a north pole-oriented and a south pole-oriented magnet are put close to one another, they will pull together so tightly, depending on the strength of the magnet, that it will take some effort to pull them apart. By contrast, one cannot force two magnets of the same polarity-- north-north, south-south-- to touch one another, no matter how hard one pushes.
Electromagnets, depending on the number of winds in the coils, and strength of the current, can be made many times stronger than the strongest natural magnet. One can set a magnetic force with a south pole-orientation immediately in front of a magnetic force with a north-pole orientation, and cause attraction. If the north- pole oriented magnetic force is anchored to a vehicle, and the force of attraction to the south-pole oriented magnetic force is strong enough, the magnetic force will tug or pull the entire vehicle forward. This is the principal of propulsion in an attractive-EMS maglev system. But in order for this to work, two other conditions must be in place. First, the vehicle must already be elevated, or floating. This too can be achieved through magnetic attraction. So, in a Electromagnetic Suspension (EMS)- positive attraction system, electromagnetic force is used for both the functions of propulsion and levitation, although a different series of magnets is dedicated to each function. Electromagnetic force is also used for a third function: guidance-- keeping the train on the magnetic track, giving it tilt, or pitch and roll when necessary, etc.
The second key condition that must be met for maglev, is that one can turn the current on and off very rapidly, and at will. Thus one can create a magnetically oriented north pole, and withdraw it back to neutral, as in the case of EMS-attractive system propulsion; or one can create a magnetically oriented north pole, and then by changing the direction of the current, create an opposite south pole polarity, in the place where one had a north pole only a fraction of a second ago, as in the case of EDS- repulsive system propulsion. Electromagnetism, as opposed to normal magnetism, allows one to do this, by turning on and off, or shifting directionality of the current. What happens is that the frequency of action is so great, that one doesn't end up with many discrete steps, but rather a process that is apparently continuous: one creates a standing electromagnetic wave.
We will look at the propulsion and levitation principles, at least schematically of the two dominant maglev systems: EMS- attraction and EDS-repulsion. Though there may be many variants of each system, all maglev research for commercial purposes is focusing on one or the other system.
However, this raises a frequently asked question: where is the motor or engine in the maglev system? The answer that there is none is not strictly accurate: there is a motor, it's just not where one would normally think to look for it. The motor of a maglev system is the interaction between the electromagnets/superconducting magnets (SCMs) and the guideway; the package of the two, and their interaction is what constitutes the motor. Otherwise, there is no standing motor aboard, as in the case of train locomotive or automobile engine.
In a normal conventional motor, say an induction motor, there are two principal parts: the stator, which is the outer circle, which is stationary, and consists of a series of windings, called the primary windings; and the rotor, which is the inner circle, which can rotate as a result of action from the stator, and which consists of a series of windings called secondary windings. The rotor is most frequently connected to a shaft which can rotate, performing work. What happens is that a magnetic force in the primary windings of the stator induces a voltage, which induces a current in the secondary windings of the rotor. The total process causes the rotor to rotate (often, in this system, the polarity of the poles of the stator are alternated very rapidly between north, south, north, etc).
There are other motors, for example, synchronous motors. But whatever the motor, in a maglev system, it is linearized, meaning that it is opened up, unwound, and stretched out, for as long as the track extends. Usually, the straightened stators, whether they be long or short, are embedded in the track, and the rotors are embedded in the electromagnetic system onboard the vehicle; but on occasion, in some systems, the roles can be reversed. This becomes important in the propulsion system.
Figures x.1 and x.2 show the principal two systems: EMS- attractive and EDS-repulsive, respectively.
In the EMS-attractive system, the electromagnets which do the work of levitation are attached on the top side of a casing that extends below and then curves back up to the rail that is in the center of the track. The rail, which is in the shape of an inverted T, is a ferromagnetic rail. When a current is passed through it, and the electromagnet switched on, there is attraction, and the levitation electromagnets, which are below the rail, raise up to meet the rail. The car levitates. The gap between the bottom of the vehicle and the rail is only 3/8" and an electronic monitoring system, by controlling the amount of attractive force, must closely control the size of the gap.
In the EDS-repulsive system, the superconducting magnets (SCMs), which do the levitating of the vehicle, are at the bottom of the vehicle, but above the track. The track or roadway is either an aluminum guideway or a set of conductive coils. The magnetic field of the superconducting magnets aboard the maglev vehicle induces an eddy current in the guideway. The polarity of the eddy current is same as the polarity of the SCMs onboard the vehicle. Repulsion results, "pushing" the vehicle away and thus up from the track. The gap between vehicle and guideway in the EDS-system is considerably wider, at 1 to 7 inches, and is also regulated (by a null-flux system). A more advanced EDS-repulsive system, worked on by the Japanese (and Americans), utilizes a U-shaped guideway, in which the vehicle nestles in between the U-shaped guideway (this makes the vehicle very stable; it can't overturn). Coils are implanted in the walls of the U- shaped guideway, called guidewalls. Thus, the guideway is not below, but out to the sides. Now the repulsion goes perpendicularly outward from the vehicle to the coils in the guidewalls. The perpendicular repulsion still provides lift.
The EMS-attractive system maglev surfs with its support magnets on the alternating magnetic field generated in the roadway. The created electromagnetic wave is actually a mobile or travelling electromagnetic wave. The EMS-attractive system is sometimes labeled a "pull" system: the vehicle is pulled forward.
Braking is done by reversing the magnetic field. Some trains also have air flaps, like airplanes, to slow down, as well as wheels that extend downward or outward to the guideway for emergency braking in the unlikely event that everything else fails.
The propulsion of the EDS-repulsive system can be described as "pull- then neutral- then push." (EDS-repulsive also usually uses a linear synchronous motor or a locally commutated motor). In the EDS system, coils or an aluminum sheet in the guideway are used for providing drive, although they also are different than the coils dedicated for the function of levitation.
The coils in the guideway are excited by an alternating, three-phase current. This produces an alternating magnetic field, or standing magnetic wave. As with EMS- attraction, sections of the guideway are excited sequentially, with the excited section being immediately in front of the maglev vehicle. Superconducting magnets onboard the maglev vehicle are attracted to the section of the guideway immediately ahead of it, pulling the vehicle forward. Then, when the vehicle is directly overhead, the direction of the current (and thus the polarity) of the particular guideway segment is changed. During the fraction of a section in which the polarity is being changed, there is effectively neither an attractive nor repulsive interaction. But once the change in polarity occurs, and while the front of the vehicle is moving forward to the next excited portion of the guideway, a repulsive force is created, pushing the vehicle from behind. This occurs-- the vehicle's movement-- in coherence with the alternating magnetic field.
So, if the EMS-attractive drive system is a "pull system," the EDS-repulsive drive system is a "pull-neutral-then push system."
There are different benefits to the EMS-attractive and the EDS-repulsive system. The EMS-attractive system has had more testing, and appears more ready to go. It also does not require a secondary suspension system, which the EDS-repulsive system does.
But there are two features of the EDS system, which make it very attractive and promising. First, the EDS-repulsive system employs superconducting magnets (SCMs), which for a variety of reasons, the EMS-attractive system cannot. The benefits are potentially large, and it will also mean development in the field of SCMs. In 1908, Kamerlingh Onnes, working at the University of Leiden in Holland, succeeded in liquefying helium by achieving a temperature of only 4.2 degrees Kelvin (or above absolute zero) for the first time.
In 1911, Onnes discovered the phenomenon of superconductivity, while exploring how far the electrical resistivity of a pure metal would decrease as the temperature dropped. He found that some materials brought down to 4.2L Kelvin exhibited virtually no resistance to an electrical current-- the current once established, continued to flow unimpeded and appeared to be capable of persisting forever: no resistance means no loss of energy through heat dissipation. It has been estimated that superconducting magnets for maglev will only have to be recharged after about 400 hours of use, or every 2 weeks, if the vehicle ran continually. By contrast, electromagnets of the EMS-attractive system require a continuous input of current to create the magnetic fields.
The importance of the discovery can be illustrated by the fact that a conventional 12 gauge copper wire cannot carry a current greater than 20 amperes because resistive energy loss and heating would melt the copper; a comparable wire of a superconducting alloy, such as niobium-titanium, can carry a current of 50,000 amperes, if kept at the temperature of liquid helium. Superconductivity is an immense benefit to maglev in terms of reducing power requirements: once the power is introduced into the system at the beginning of the ride, it stays, without loss, for the whole ride, cutting down hugely on the power requirement per passenger-mile travelled.
Op Cut: [In 1987, Dr. Paul Chu of the University of Houston, announced the he succeeded in producing superconductivity, using liquid nitrogen, at a temperature of 93 o K. This means superconducting takes place at a higher temperature, ultimately making it less costly, because one needs less cryogenics. EDS- maglev can proceed with superconductivity at it now exists. If what Dr. Chu discovered can be commercialized, that will make the process even more efficient and cheaper.]
A second advantage of EDS-maglev is that it has a larger air gap than EMS-maglev, meaning that the system should handle wind- gusts, or hilly terrain, or earthquakes, or other disturbances, much more smoothly. It is also believed, that hypothetically, EDS- maglev will be able to attain higher speeds in the long-run.
However, whichever system of maglev one chooses, it is light- years above all other existing conventional modes of ground transport. According to a Rand Corporation study, referred to earlier in this pamphlet, a second generation maglev system that travels in an evacuated tunnel-- i.e., a vacuum, could potentially travel the 2,800 miles between New York City and Los Angeles in less than an hour. No ground-based form of transport, and no commercial airplane can do that, or will be able to for some time to come.
Each industry consortium has released preliminary studies of their design for maglev. Three are using EDS-repulsive; the Grumman Corporation is using EMS-attractive. All four have released concept designs that show impressive ideas, including innovative improvements over the relevant German or Japanese models, or entirely new systems. All could be built using American engineering and manufacturing.
But the problem is that no money has been awarded yet by the National Maglev Initiative to build a maglev prototype development program, including a maglev test track. America has no maglev program.
However, whichever path America chooses-- whether America licenses maglev from the German Transrapid, as is proposed in Pennsylvania, or develops its own system-- the crucial point is that maglev will set off a transportation and broader scientific explosion.
|Top of Page||Exploring Space ...||Site Map||Overview Page|
Readings from the American Almanac. Contact us at: firstname.lastname@example.org.