Today’s High-Speed Trains vs. Magnetically Suspended Trains
Difference Between Today’s High-Speed Trains And Magnetically Suspended Trains
Several countries have developed high-speed intercity passenger trains. The newest systems are able to reach speeds in excess of 200 miles (322 kilometers) per hour.
In Japan, the Shinkansen Bullet Train, in operation since the 1960s, attains speeds of more than 185 miles (300 kilometers) per hour. The electric, self-propelled, multiple-unit car system will be upgraded with trains capable of reaching 224 miles (360 kilometers) per hour over the next several years. Japan’s network of high-speed rail lines also continues to expand.
The TGV, for Train à Grande Vitesse, is France’s high-speed passenger train, operating at speeds in excess of 185 miles per hour. Locomotives at each end pull the train in either direction. The TGV connects more than 150 communities, linking Paris to such cities as London, Brussels, Zurich, and Milan. In April 2007, the newly modified TGV set a world speed record of more than 357 miles (575 kilometers) per hour.
Both the TGV and Shinkansen trains use a hanging-wire system to supply electricity. While the TGV travels on dedicated specially built tracks, its trains do mix with other trains on conventional tracks for the last few miles near cities.
Another European high-speed train, the Eurostar, takes passengers from London (beneath the English Channel, via the Chunnel) to Paris and Brussels. The trip to Paris takes 3 hours, and riders can go from London to Brussels in 2 hours and 40 minutes. Each train has 18 cars, which can seat as many passengers as two jumbo jets.
In the United States, Amtrak runs a high-speed train on its routes between Washington, D.C., and Boston. The sleekly designed Acela Express uses giant alternating-current (AC) wheel motors, which provide smoother, more powerful acceleration than the direct-current (DC) models that have been used on U.S. trains for decades. AC motors also involve simpler machinery and require far less maintenance. The Acela, whose top speed is 150 miles (240 kilometers) per hour, travels from New York to Boston in 3 hours and 20 minutes—taking about 35 percent less time than is typical for standard train service.
Acela has had its share of mechanical problems, perhaps related to the structural strain of high-speed rail travel. In 2002, the trains were sidelined because of cracks in some of their shock-absorber assemblies. In April 2005, more cracks were detected, this time in several disc brake rotors, and Amtrak temporarily suspended Acela service. Slower passenger trains took over the Northeast route until the 20-train Acela fleet was again fully operational.
Magnetically Suspended Trains
The wheel-to-track interface is the major obstacle to the further development of trains that travel at high speeds. This interface provides traction, braking, and guidance capabilities, but imperfections in track and wheels lower the performance level. Magnetic systems allow trains to travel above the track without touching it, thus eliminating the problem.
Magnetic systems, often referred to as maglev systems, were proposed by researchers in the 1930s. Experimental versions have been developed through efforts by Japan, Germany, Britain, and the United States since the 1960s. Japan and Germany have invested the most on research and the development of prototypes, and have designed hardware that uses magnetism to levitate, guide, and propel ground vehicles.
The maglev system both levitates and guides the vehicle. Magnets also propel the train through the use of electric motors. At present, there are two different systems being developed: electromagnetic suspension (EMS), investigated by researchers in Germany, and electrodynamic suspension (EDS), used in Japan.
Germany has developed Transrapid—an “attractive” electromagnetic system, comprised of an electromagnet attracted to a nonenergized magnetic surface. In 1974, a 20-ton vehicle was built and tested at speeds up to 150 miles (240 kilometers) per hour. In 1979, a maglev system was exhibited at the Hamburg Trade Fair; it featured a two-section vehicle 85 feet (26 meters) long, weighing 80,000 pounds (36,000 kilograms), and able to transport 75 passengers at 50 miles (80 kilometers) per hour over a short elevated guideway. In China, Transrapid trains, traveling more than 250 miles (400 kilometers) per hour, shuttle passengers to and from the airport outside of Shanghai, a distance of about 19 miles (30 kilometers). In 2007, Chinese officials announced plans to expand the high-speed maglev line to the site of the 2010 World Expo along the banks of the Huangpu River, which runs through the heart of Shanghai. Another joint Sino-German project is the planned extension of Shanghai’s maglev line by some 112 miles (180 kilometers) to the city of Guangzhou.
During the 1970s, the U.S. company Boeing Aerospace developed a 90-foot (27-meter) test track with a 12,000-pound (5,400-kilogram) simulated car using the attractive electromagnetic system. Without strong government support, however, industry interest in maglevs ebbed and research remained at a standstill for many years in the United States. Because of high initial costs and lack of public enthusiasm, U.S. maglev projects have been slow to develop. Even so, in 2007, California officials were evaluating a proposed maglev line that would connect Sacramento to San Diego, passing through the cities of San Francisco and Los Angeles. Other possible U.S. maglev sites include Chicago and a corridor between Anaheim, California, and Las Vegas.
In Japan, researchers and engineers have taken a unique approach to maglev design, focusing on the development of an electrodynamic or repulsive system, which uses two electromagnets to repulse each other. Onboard, cryogenically cooled (that is, cooled to near absolute zero, which is −460° F or −273° C), superconducting magnets induce eddy currents in the ground coils as the vehicle moves. The magnets, made of superconducting materials, lose all electrical resistance at temperatures near absolute zero. These materials are called superconductors. Another property of superconductors is that they exclude magnetic fields.
The eddy currents in the ground coils produce a repulsive force that levitates the car. The vehicle must be traveling at a high rate of speed for this to happen. At lower speeds, a set of ground wheels is required. Japan has tested this principle using a number of unmanned maglev trains—several of which have reached velocities in excess of 300 miles (480 kilometers) per hour. The development of this transportation system is ongoing, as is advanced testing of the trains’ safety and durability at high speeds.
One of the main problems with the Japanese design is that it requires an expensive cooling system. The development of new superconducting elements that work at much higher temperatures than other substances will revolutionize the development of electrodynamic maglev systems. These materials have the potential to make the use of superconducting magnets much cheaper, since they will not require costly coolants.
Both the electromagnetic and electrodynamic systems have strengths and weaknesses. The electromagnetic system requires a small gap between the magnets. In addition, the surface has to be about 3/8-inch (10 millimeters) thick; this requires a closer guideway tolerance. Development of a gap sensor to handle this problem has been a major undertaking. The small gap needs less power for levitation and there is less magnetic drag, further reducing power requirements. The electromagnetic system also uses a simpler guideway (track), and a simpler system on board since it has no supercooled magnets or low-speed running gear.
The electrodynamic system can have an air gap up to 6 inches (15 centimeters), requiring less tolerance in the guideway. The main problem is the need for cryogenically cooled superconducting magnets. If the development of the new warm-temperature superconducting materials yields a product that reduces the cooling costs for the magnets, the system will gain plausibility.