The Basics of Magnetic Levitated Trains (Maglev)

A Shanghai Maglev traveling through a Pudong neighborhood at high speed. Getty Images/Christian Petersen-Clausen

Magnetic levitation (maglev) is a relatively new transportation technology in which non-contacting vehicles travel safely at speeds of 250 to 300 miles-per-hour or higher while suspended, guided, and propelled above a guideway by magnetic fields. The guideway is the physical structure along which maglev vehicles are levitated. Various guideway configurations, e.g., T-shaped, U-shaped, Y-shaped, and box-beam, made of steel, concrete, or aluminum, have been proposed.

There are three primary functions basic to maglev technology: (1) levitation or suspension; (2) propulsion; and (3) guidance. In most current designs, magnetic forces are used to perform all three functions, although a nonmagnetic source of propulsion could be used. No consensus exists on an optimum design to perform each of the primary functions.

Suspension Systems

Electromagnetic suspension (EMS) is an attractive force levitation system whereby electromagnets on the vehicle interact with and are attracted to ferromagnetic rails on the guideway. EMS was made practical by advances in electronic control systems that maintain the air gap between vehicle and guideway, thus preventing contact.

Variations in payload weight, dynamic loads, and guideway irregularities are compensated for by changing the magnetic field in response to vehicle/guideway air gap measurements.

Electrodynamic suspension (EDS) employs magnets on the moving vehicle to induce currents in the guideway.

Resulting repulsive force produces inherently stable vehicle support and guidance because the magnetic repulsion increases as the vehicle/guideway gap decreases. However, the vehicle must be equipped with wheels or other forms of support for "takeoff" and "landing" because the EDS will not levitate at speeds below approximately 25 mph.

EDS has progressed with advances in cryogenics and superconducting magnet technology.

Propulsion Systems

"Long-stator" propulsion using an electrically powered linear motor winding in the guideway appears to be the favored option for high-speed maglev systems. It is also the most expensive because of higher guideway construction costs.

"Short-stator" propulsion uses a linear induction motor (LIM) winding onboard and a passive guideway. While short-stator propulsion reduces guideway costs, the LIM is heavy and reduces vehicle payload capacity, resulting in higher operating costs and lower revenue potential compared to the long-stator propulsion. A third alternative is a nonmagnetic energy source (gas turbine or turboprop) but this, too, results in a heavy vehicle and reduced operating efficiency.

Guidance Systems

Guidance or steering refers to the sideward forces that are required to make the vehicle follow the guideway. The necessary forces are supplied in an exactly analogous fashion to the suspension forces, either attractive or repulsive. The same magnets on board the vehicle, which supply lift, can be used concurrently for guidance or separate guidance magnets can be used.

Maglev and U.S. Transportation

Maglev systems could offer an attractive transportation alternative for many time sensitive trips of 100 to 600 miles in length, thereby reducing air and highway congestion, air pollution, and energy use, and releasing slots for more efficient long-haul service at crowded airports.

The potential value of maglev technology was recognized in the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA).

Before the passage of the ISTEA, Congress had appropriated $26.2 million to identify maglev system concepts for use in the United States and to assess the technical and economic feasibility of these systems. Studies were also directed toward determining the role of maglev in improving intercity transportation in the United States. Subsequently, an additional $9.8 million were appropriated to complete the NMI Studies.

Why Maglev?

What are the attributes of maglev that commend its consideration by transportation planners?

Faster trips - high peak speed and high acceleration/braking enable average speeds three to four times the national highway speed limit of 65 mph (30 m/s) and lower door-to-door trip time than high-speed rail or air (for trips under about 300 miles or 500 km).

Still higher speeds are feasible. Maglev takes up where high-speed rail leaves off, permitting speeds of 250 to 300 mph (112 to 134 m/s) and higher.

Maglev has high reliability and less susceptible to congestion and weather conditions than air or highway travel. Variance from schedule can average less than one minute based on foreign high-speed rail experience. This means intra and intermodal connecting times can be reduced to a few minutes (rather than the half-hour or more required with airlines and Amtrak at present) and that appointments can safely be scheduled without having to consider delays.

Maglev gives petroleum independence - with respect to air and auto because of Maglev being electrically powered. Petroleum is unnecessary for the production of electricity. In 1990, less than 5 percent of the Nation's electricity was derived from petroleum whereas the petroleum used by both the air and automobile modes comes primarily from foreign sources.

Maglev is less polluting - with respect to air and auto, again because of being electrically powered. Emissions can be controlled more effectively at the source of electric power generation than at the many points of consumption, such as with air and automobile usage.

Maglev has a higher capacity than air travel with at least 12,000 passengers per hour in each direction. There is the potential for even higher capacities at 3 to 4 minute headways. Maglev provides sufficient capacity to accommodate traffic growth well into the twenty-first century and to provide an alternative to air and auto in the event of an oil availability crisis.

Maglev has high safety - both perceived and actual, based on foreign experience.

Maglev has convenience - due to high frequency of service and the ability to serve central business districts, airports, and other major metropolitan area nodes.

Maglev has improved comfort - with respect to air due to greater roominess, which allows separate dining and conference areas with freedom to move around. The absence of air turbulence ensures a consistently smooth ride.

Maglev Evolution

The concept of magnetically levitated trains was first identified at the turn of the century by two Americans, Robert Goddard and Emile Bachelet. By the 1930s, Germany's Hermann Kemper was developing a concept and demonstrating the use of magnetic fields to combine the advantages of trains and airplanes. In 1968, Americans James R. Powell and Gordon T. Danby were granted a patent on their design for a magnetic levitation train.

Under the High-Speed Ground Transportation Act of 1965, the FRA funded a wide range of research into all forms of HSGT through the early 1970s. In 1971, the FRA awarded contracts to the Ford Motor Company and the Stanford Research Institute for analytical and experimental development of EMS and EDS systems. FRA-sponsored research led to the development of the linear electrical motor, the motive power used by all current maglev prototypes. In 1975, after Federal funding for high-speed maglev research in the United States was suspended, industry virtually abandoned its interest in maglev; however, research in low-speed maglev continued in the United States until 1986.

Over the past two decades, research and development programs in maglev technology have been conducted by several countries including: Great Britain, Canada, Germany, and Japan. Germany and Japan have invested over $1 billion each to develop and demonstrate maglev technology for HSGT.

The German EMS maglev design, Transrapid (TR07), was certified for operation by the German Government in December 1991. A maglev line between Hamburg and Berlin is under consideration in Germany with private financing and potentially with additional support from individual states in northern Germany along the proposed route. The line would connect with the high-speed Intercity Express (ICE) train as well as conventional trains. The TR07 has been tested extensively in Emsland, Germany, and is the only high-speed maglev system in the world ready for revenue service. The TR07 is planned for implementation in Orlando, Florida.

The EDS concept under development in Japan uses a superconducting magnet system. A decision will be made in 1997 whether to use maglev for the new Chuo line between Tokyo and Osaka.

The National Maglev Initiative (NMI)

Since the termination of Federal support in 1975, there was little research into high-speed maglev technology in the United States until 1990 when the National Maglev Initiative (NMI) was established. The NMI is a cooperative effort of the FRA of the DOT, the USACE, and the DOE, with support from other agencies. The purpose of the NMI was to evaluate the potential for maglev to improve intercity transportation and to develop the information necessary for the Administration and the Congress to determine the appropriate role for the Federal Government in advancing this technology.

In fact, from its inception, the U.S. Government has aided and promoted innovative transportation for economic, political, and social development reasons. There are numerous examples. In the nineteenth century, the Federal Government encouraged railroad development to establish transcontinental links through such actions as the massive land grant to the Illinois Central-Mobile Ohio Railroads in 1850. Beginning in the 1920s, the Federal Government provided commercial stimulus to the new technology of aviation through contracts for airmail routes and funds that paid for emergency landing fields, route lighting, weather reporting, and communications. Later in the twentieth century, Federal funds were used to construct the Interstate Highway System and assist States and municipalities in the construction and operation of airports. In 1971, the Federal Government formed Amtrak to ensure rail passenger service for the United States.

Assessment of Maglev Technology

In order to determine the technical feasibility of deploying maglev in the United States, the NMI Office performed a comprehensive assessment of the state-of-the-art of maglev technology.

Over the past two decades various ground transportation systems have been developed overseas, having operational speeds in excess of 150 mph (67 m/s), compared to 125 mph (56 m/s) for the U.S. Metroliner. Several steel-wheel-on-rail trains can maintain a speed of 167 to 186 mph (75 to 83 m/s), most notably the Japanese Series 300 Shinkansen, the German ICE, and the French TGV. The German Transrapid Maglev train has demonstrated a speed of 270 mph (121 m/s) on a test track, and the Japanese have operated a maglev test car at 321 mph (144 m/s). The following are descriptions of the French, German, and Japanese systems used for comparison to the U.S. Maglev (USML) SCD concepts.  

French Train a Grande Vitesse (TGV)

The French National Railway's TGV is representative of the current generation of high-speed, steel-wheel-on-rail trains. The TGV has been in service for 12 years on the Paris-Lyon (PSE) route and for 3 years on an initial portion of the Paris-Bordeaux (Atlantique) route. The Atlantique train consists of ten passenger cars with a power car at each end.  The power cars use synchronous rotary traction motors for propulsion. Roof mounted pantographs collect electric power from an overhead catenary. Cruise speed is 186 mph (83 m/s). The train is nontilting and, thus, requires a reasonably straight route alignment to sustain high speed. Although the operator controls the train speed, interlocks exist including automatic overspeed protection and enforced braking. Braking is by a combination of rheostat brakes and axle-mounted disc brakes. All axles possess antilock braking. Power axles have anti-slip control. The TGV track structure is that of a conventional standard-gauge railroad with a well-engineered base (compacted granular materials). The track consists of continuous-welded rail on concrete/steel ties with elastic fasteners. Its high-speed switch is a conventional swing-nose turnout. The TGV operates on pre-existing tracks, but at a substantially reduced speed. Because of its high speed, high power, and antiwheel slip control, the TGV can climb grades that are about twice as great as normal in U.S. railroad practice and, thus, can follow the gently rolling terrain of France without extensive and expensive viaducts and tunnels.

German TR07

The German TR07 is the high-speed Maglev system nearest to commercial readiness. If financing can be obtained, ground breaking will take place in Florida in 1993 for a 14-mile (23 km) shuttle between Orlando International Airport and the amusement zone at International Drive. The TR07 system is also under consideration for a high-speed link between Hamburg and Berlin and between downtown Pittsburgh and the airport. As the designation suggests, TR07 was preceded by at least six earlier models. In the early seventies, German firms, including Krauss-Maffei, MBB and Siemens, tested full-scale versions of an air cushion vehicle (TR03) and a repulsion maglev vehicle using superconducting magnets. After a decision was made to concentrate on attraction maglev in 1977, advancement proceeded in significant increments, with the system evolving from linear induction motor (LIM) propulsion with wayside power collection to the linear synchronous motor (LSM), which employs variable frequency, electrically powered coils on the guideway. TR05 functioned as a people mover at the International Traffic Fair Hamburg in 1979, carrying 50,000 passengers and providing valuable operating experience.

The TR07, which operates on 19.6 miles (31.5 km) of guideway at the Emsland test track in northwest Germany, is the culmination of nearly 25 years of German Maglev development, costing over $1 billion. It is a sophisticated EMS system, using separate conventional iron-core attracting electromagnets to generate vehicle lift and guidance. The vehicle wraps around a T-shaped guideway. The TR07 guideway uses steel or concrete beams constructed and erected to very tight tolerances. Control systems regulate levitation and guidance forces to maintain an inch gap (8 to 10 mm) between the magnets and the iron "tracks" on the guideway. Attraction between vehicle magnets and edge-mounted guideway rails provide guidance. Attraction between a second set of vehicle magnets and the propulsion stator packs underneath the guideway generate lift. The lift magnets also serve as the secondary or rotor of a LSM, whose primary or stator is an electrical winding running the length of the guideway. TR07 uses two or more nontilting vehicles in a consist. TR07 propulsion is by a long-stator LSM. Guideway stator windings generate a traveling wave that interacts with the vehicle levitation magnets for synchronous propulsion. Centrally controlled wayside stations provide the requisite variable-frequency, variable-voltage power to the LSM. Primary braking is regenerative through the LSM, with eddy-current braking and high-friction skids for emergencies. TR07 has demonstrated safe operation at 270 mph (121 m/s) on the Emsland track. It is designed for cruise speeds of 311 mph (139 m/s).

Japanese High-Speed Maglev

The Japanese have spent over $1 billion developing both attraction and repulsion maglev systems. The HSST attraction system, developed by a consortium often identified with Japan Airlines, is actually a series of vehicles designed for 100, 200, and 300 km/h. Sixty miles-per-hour (100 km/h) HSST Maglevs have transported over two million passengers at several Expos in Japan and the 1989 Canada Transport Expo in Vancouver. The high speed Japanese repulsion Maglev system is under development by Railway Technical Research Institute (RTRI), the research arm of the newly privatized Japan Rail Group. RTRI's ML500 research vehicle achieved the world high-speed guided ground vehicle record of 321 mph (144 m/s) in December 1979, a record that still stands, although a specially modified French TGV rail train has come close. A manned three-car MLU001 began testing in 1982. Subsequently, the single car MLU002 was destroyed by fire in 1991. Its replacement, the MLU002N, is being used to test the sidewall levitation that is planned for eventual revenue system use. The principal activity at present is the construction of a $2 billion, 27-mile (43 km) maglev test line through the mountains of Yamanashi Prefecture, where testing of a revenue prototype is scheduled to commence in 1994.

The Central Japan Railway Company plans to begin building a second high-speed line from Tokyo to Osaka on a new route (including the Yamanashi test section) starting in 1997. This will provide relief for the highly profitable Tokaido Shinkansen, which is nearing saturation and needs rehabilitation. To provide ever improving service, as well as to forestall encroachment by the airlines on its present 85 percent market share, higher speeds than the present 171 mph (76 m/s) are regarded as necessary. Although the design speed of the first generation maglev system is 311 mph (139 m/s), speeds up to 500 mph (223 m/s) are projected for future systems. Repulsion maglev has been chosen over attraction maglev because of its reputed higher speed potential and because the larger air gap accommodates the ground motion experienced in Japan's earthquake-prone territory. The design of Japan's repulsion system is not firm. A 1991 cost estimate by Japan's Central Railway Company, which would own the line, indicates that the new high-speed line through the mountainous terrain north of Mt. Fuji would be very expensive, about $100 million per mile (8 million yen per meter) for a conventional railway. A maglev system would cost 25 percent more. A significant part of the expense is the cost of acquiring surface and subsurface ROW. Knowledge of the technical details of Japan's high-speed Maglev is sparse. What is known is that it will have superconducting magnets in bogies with sidewall levitation, linear synchronous propulsion using guideway coils, and a cruise speed of 311 mph (139 m/s).

U.S. Contractors' Maglev Concepts (SCDs)

Three of the four SCD concepts use an EDS system in which superconducting magnets on the vehicle induce repulsive lift and guidance forces through movement along a system of passive conductors mounted on the guideway. The fourth SCD concept uses an EMS system similar to the German TR07. In this concept, attraction forces generate lift and guide the vehicle along the guideway. However, unlike TR07, which uses conventional magnets, the attraction forces of the SCD EMS concept are produced by superconducting magnets. The following individual descriptions highlight the significant features of the four U.S. SCDs.

Bechtel SCD

The Bechtel concept is an EDS system that uses a novel configuration of vehicle-mounted, flux-canceling magnets.  The vehicle contains six sets of eight superconducting magnets per side and straddles a concrete box-beam guideway. Interaction between the vehicle magnets and a laminated aluminum ladder on each guideway sidewall generates lift.  Similar interaction with guideway mounted nullflux coils provides guidance. LSM propulsion windings, also attached to the guideway sidewalls, interact with vehicle magnets to produce thrust. Centrally controlled wayside stations provide the required variable-frequency, variable-voltage power to the LSM. The Bechtel vehicle consists of a single car with an inner tilting shell. It uses aerodynamic control surfaces to augment magnetic guidance forces. In an emergency, it delevitates onto air-bearing pads. The guideway consists of a post-tensioned concrete box girder. Because of high magnetic fields, the concept calls for nonmagnetic, fiber-reinforced plastic (FRP) post-tensioning rods and stirrups in the upper portion of the box beam. The switch is a bendable beam constructed entirely of FRP.

Foster-Miller SCD

The Foster-Miller concept is an EDS similar to the Japanese high-speed Maglev, but has some additional features to improve potential performance. The Foster-Miller concept has a vehicle tilting design that would allow it to operate through curves faster than the Japanese system for the same level of passenger comfort. Like the Japanese system, the Foster-Miller concept uses superconducting vehicle magnets to generate lift by interacting with null-flux levitation coils located in the sidewalls of a U-shaped guideway. Magnet interaction with guideway-mounted, electrical propulsion coils provides null-flux guidance. Its innovative propulsion scheme is called a locally commutated linear synchronous motor (LCLSM). Individual "H-bridge" inverters sequentially energize propulsion coils directly under the bogies. The inverters synthesize a magnetic wave that travels along the guideway at the same speed as the vehicle. The Foster-Miller vehicle is composed of articulated passenger modules and tail and nose sections that create multiple-car "consists." The modules have magnet bogies at each end that they share with adjacent cars. Each bogie contains four magnets per side. The U-shaped guideway consists of two parallel, post-tensioned concrete beams joined transversely by precast concrete diaphragms. To avoid adverse magnetic effects, the upper post-tensioning rods are FRP. The high-speed switch uses switched null-flux coils to guide the vehicle through a vertical turnout. Thus, the Foster-Miller switch requires no moving structural members.

Grumman SCD

The Grumman concept is an EMS with similarities to the German TR07. However, Grumman's vehicles wrap around a Y-shaped guideway and use a common set of vehicle magnets for levitation, propulsion, and guidance.  Guideway rails are ferromagnetic and have LSM windings for propulsion. The vehicle magnets are superconducting coils around horseshoe-shaped iron cores. The pole faces are attracted to iron rails on the underside of the guideway. Nonsuperconducting control coils on each iron-core leg modulate levitation and guidance forces to maintain a 1.6-inch (40 mm) air gap. No secondary suspension is required to maintain adequate ride quality. Propulsion is by conventional LSM embedded in the guideway rail. Grumman vehicles may be single or multi-car consists with tilt capability. The innovative guideway superstructure consists of slender Y-shaped guideway sections (one for each direction) mounted by outriggers every 15-feet to a 90-foot (4.5 m to a 27 m) spline girder. The structural spline girder serves both directions. Switching is accomplished with a TR07-style bending guideway beam, shortened by use of a sliding or rotating section.

Magneplane SCD

The Magneplane concept is a single-vehicle EDS using a trough-shaped 0.8-inch (20 mm) thick aluminum guideway for sheet levitation and guidance. Magneplane vehicles can self-bank up to 45 degrees in curves. Earlier laboratory work on this concept validated the levitation, guidance, and propulsion schemes. Superconducting levitation and propulsion magnets are grouped in bogies at the front and rear of the vehicle. The centerline magnets interact with conventional LSM windings for propulsion and generate some electromagnetic "roll-righting torque" called the keel effect. The magnets on the sides of each bogie react against the aluminum guideway sheets to provide levitation. The Magneplane vehicle uses aerodynamic control surfaces to provide active motion damping. The aluminum levitation sheets in the guideway trough form the tops of two structural aluminum box beams. These box beams are supported directly on piers. The high-speed switch uses switched null-flux coils to guide the vehicle through a fork in the guideway trough. Thus, the Magneplane switch requires no moving structural members.

Sources: National Transportation Library http://ntl.bts.gov/​