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Maglev (Magnetic Levitation)

Maglev Background

Magnetic levitation (maglev) is an innovative transportation technology. It is sometimes said to be the first fundamental innovation in the field of railroad technology since the invention of the railway. A high speed maglev train uses non-contact magnetic levitation, guidance and propulsion systems and has no wheels, axles and transmission. The replacement of mechanical components by wear-free electronics overcomes the technical restrictions of wheel-on-rail technology. Compared with traditional railways, maglev systems have features that could constitute an attractive transportation alternative:

• High speed. Capable of traveling safely at speeds of 250 to 300 miles-per-hour (112m/s to 134m/s) or higher, which is four times the national highway speed limit of 65 mph (30m/s). Maglev could offer a convenient alternative for intercity travelers.

• High safety. Despite high speeds, passengers may be safer than in other transportation systems. The electromagnetically suspended vehicle is wrapped around the guideway and therefore virtually impossible to derail. Elevated guideways ensure that no obstacles can be in the way.

• Less pollution. As maglev is electrically powered, there is no direct air pollution as with airplanes and automobiles. It is easier and more effective to control emissions at the source of electric power generation rather than at many points of consumption. Due to its non-contact technology, there is neither rolling nor engine noise.

• Low energy consumption. With non-contact technology, there is no energy loss due to the wheel-guideway friction. The vehicle weight is lower due to the absence of wheels, axles and engine.

• High capacity. Maglev systems can provide sufficient capacity to accommodate traffic growth. They can help relieve air and highway congestion by diverting a portion of highway trips and by substituting for short air trips.

There are three primary functions in maglev technology: (1) levitation or suspension; (2) propulsion; (3) guidance. Current maglev system design uses magnetic forces to perform all three functions.

Currently there are two principal different designs of suspension systems. One design is called ElectroDynamic Suspension (EDS). The Japan Railway Technical Research Institute’s (RTRI) MLU-series maglev design is an EDS system.

The EDS has onboard magnets that induce current in the guideway sidewalls while the vehicle is moving. Resulting repulsive forces produce inherently stable vehicle support and guidance, because the magnetic repulsion increases as the vehicle/guideway gap (both vertical and lateral) decreases. The magnetized coil running along the track repels the large magnets mounted on the train's undercarriage, allowing the train to levitate between 0.39 and 3.93 inches (1 to 10 cm) above the guideway. However, some form of support is needed for taking off and landing, since the EDS cannot be levitated at speeds lower than 62 mph.

The second design is called ElectroMagnetic Suspension (EMS). The German technology, the Transrapid International (TRI) maglev system, is based on an EMS design, which is an attractive force levitation system. Electronically controlled support magnets are located on both sides along the entire length of the vehicle. Ferromagnetic stator packs are mounted to the underside of the guideway. The electromagnets on the vehicle interact with and are attracted to ferromagnetic rails on the guideway. Electromagnets attached to the train's undercarriage are directed up toward the guideway, which levitates the train about 1/3 inch (1 cm) above the guideway and keeps the train levitated even when it's not moving. The attractive force produces inherently unstable vehicle support because the attractive force increases as the vehicle/guideway gap decreases. An electronic control system is equipped to maintain the vehicle/guideway gap and prevent contact. This involves the complex problems of gap sensing, analog and digital control, and precision construction.

Guidance magnets are located on both sides along the entire length of the vehicle to keep the vehicle laterally stable during travel on the track. Electronic control systems control the clearance (nominally 10 mm). The levitation system uses on-board batteries that are independent of the propulsion system. The vehicle is capable of hovering up to one hour without external energy. While traveling, the on-board batteries are recharged by linear generators integrated into the support magnets.

A synchronous, long stator linear motor is used in the Transrapid maglev system both for propulsion and braking. It functions like a rotating electric motor whose stator is cut open and stretched along under the guideway. Inside the motor windings, alternating current is generating a magnetic traveling field that moves the vehicle without contact. The support magnets in the vehicle function as the excitation portion (rotor). The speed can be continuously regulated by varying the frequency of the alternating current. If the direction of the traveling field is reversed, the motor becomes a generator which brakes the vehicle without any contact.

Figure 1.5 schematically shows that, in accordance with Lenz’s Law, the interaction of the levitation field with the current in the slots of the rail results in propulsion or braking force. During the motion of the magnet along the rail, the linear generator winding of the main pole is coupled with a non-constant flux, which induces a voltage and reloads the on-board batteries. The generation process begins in the range of 15 km/h and equals the losses of the magnetic suspension systems at 90 km/h. The whole energy losses of the vehicle are compensated at a velocity of 110 km/h and the batteries are reloaded. Thus the levitation magnet integrates three tasks: levitation, propulsion and transfer of energy to the vehicle.

The maglev train hovers over a double track guideway. It can be mounted either at-grade or elevated on columns and consists of individual steel or concrete beams.

One major difference between Japanese and German maglev trains is that the Japanese trains use super-cooled, superconducting electromagnets. In the EMS system, which uses standard electromagnets, the coils only conduct electricity when a power supply is present. But the technical requirements for Japanese maglev train are higher than in the case of attractive magnetic forces for which only one side of the system needs to be equipped with electrical wires (the vehicle) for vehicle levitation.

Another difference between the systems is that the Japanese trains levitate nearly 4 inches (10 cm) above the guideway. Compared with German trains, which are levitated only about 1/3 inch (1cm), this great gap will generate high stray magnetic fields. Since the gap is much smaller in the EMS system, the force density is sufficiently high and the power consumption is very low even with ordinary electromagnets. It is not necessary to use superconducting coils. While levitation can be achieved at low speed and even at standstill for an EMS system, maglev trains using EDS system must roll on rubber tires until they reach a lift-off speed of about 62 mph (100 kph).

Maglev Progress

Germany (TRI) has been investigating electromagnetic levitation since 1969, and commissioned the TR02 in 1971. The eighth generation vehicle, the TR08, which operates on 19.6 miles (31.5km) of guideway at the Emsland test track in northwest Germany, is the culmination of nearly 30 years of German maglev development. Control systems regulate levitation and guidance forces to maintain a 1cm (0.4in) gap between the magnets and the iron tracks on the guideway. Some of its precursor prototype vehicles, the TR07 and the TR06, have been tested at the Transrapid Test Facility (TVE) for more than 15 years.

Construction work of the Shanghai Transrapid line began in March 2001. After only 22 months of construction time, the world's first commercially operated Transrapid train made its successful maiden trip on December, 31 2002. On December 29, 2003, the world’s first commercial Transrapid line with a five section train started scheduled operation in Shanghai. The Shanghai maglev system travels on a 30km double-track elevated guideway, connecting LongYang Station in Shanghai to Pudong International Airport. The journey time is under 8 minutes. Regardless of the load and speed, the onboard control system maintains a 10mm gap with a ±2mm tolerance between the vehicle’s support magnets and the guideway’s stators and between the guidance magnets and the steel guide rails. A hybrid girder design is used to combine the low cost of concrete with the precision manufacturing offered by steel. The I-shaped hybrid girder is 25m long, 2.8 wide, 2.2m high and weighs 1.86MN with a reinforced concrete center girder and bolted steel cantilevers. The girders were milled to a precision of 0.2mm.. Engineers evaluated the girder with respect to as many as 14,000 load cases by consideration of the deflection, dynamic strength and thermal expansion. The reinforced concrete support piers are designed to withstand the seismic forces of earthquakes up to 7.5 on the Richter scale. The maximum allowable total deformation of the guideway is 10mm, which can come from the settlements caused by consolidation or creep, by dead load, by cyclic loads from the vehicles or by dynamic loads during operation. "Three-way" bearings are installed between the guideways to allow alignment corrections. The Chinese government intends to link Shanghai to the city of Hangzhou, 193km to the southwest, which would create the world’s first intercity maglev line.

In Germany, starting in 2009, the Transrapid will connect Munich's city center with "Franz-Josef Strauß" Airport. The construction of the Shanghai Transrapid line and the decision on the maglev projects in Germany have given credibility to the innovative rail system. In the U.S., Congress established the Maglev Deployment Program in 1998 as part of the Transportation Equity Act for the 21st Century (TEA-21) with the expressed purpose of building a maglev demonstration project. Six projects are about to be decided on: a 60 kilometer long connection between Baltimore and Washington, a 76 kilometer long airport link in Pittsburgh, two in Southern California, one from Las Vegas to Anaheim, California, and one from Atlanta to Chattanooga, Tennessee.

[Source: Huiguang Dai, “Dynamic Behavior of Maglev Vehicle/Guideway System with Control”, Department of Civil Engineering Case Western Reserve University, August, 2005.]



Maglev (Magnetic Levitation) Maglev Background Magnetic levitation (maglev) is an innovative transportation technology. It is sometimes said to be the first fundamental innovation in the field of railroad technology since the invention of the railway. A high speed maglev train uses non-contact magnetic levitation, guidance and propulsion systems and has no wheels, axles and transmission. The replacement of mechanical components by wear-free electronics overcomes the technical restrictions of wheel-on-rail technology. Compared with traditional railways, maglev systems have features that could constitute an attractive transportation alternative: • High speed. Capable of traveling safely at speeds of 250 to 300 miles-per-hour (112m/s to 134m/s) or higher, which is four times the national highway speed limit of 65 mph (30m/s). Maglev could offer a convenient alternative for intercity travelers. • High safety. Despite high speeds, passengers may be safer than in other transportation systems. The electromagnetically suspended vehicle is wrapped around the guideway and therefore virtually impossible to derail. Elevated guideways ensure that no obstacles can be in the way. • Less pollution. As maglev is electrically powered, there is no direct air pollution as with airplanes and automobiles. It is easier and more effective to control emissions at the source of electric power generation rather than at many points of consumption. Due to its non-contact technology, there is neither rolling nor engine noise. • Low energy consumption. With non-contact technology, there is no energy loss due to the wheel-guideway friction. The vehicle weight is lower due to the absence of wheels, axles and engine. • High capacity. Maglev systems can provide sufficient capacity to accommodate traffic growth. They can help relieve air and highway congestion by diverting a portion of highway trips and by substituting for short air trips. There are three primary functions in maglev technology: (1) levitation or suspension; (2) propulsion; (3) guidance. Current maglev system design uses magnetic forces to perform all three functions. Currently there are two principal different designs of suspension systems. One design is called ElectroDynamic Suspension (EDS). The Japan Railway Technical Research Institute’s (RTRI) MLU-series maglev design is an EDS system. The EDS has onboard magnets that induce current in the guideway sidewalls while the vehicle is moving. Resulting repulsive forces produce inherently stable vehicle support and guidance, because the magnetic repulsion increases as the vehicle/guideway gap (both vertical and lateral) decreases. The magnetized coil running along the track repels the large magnets mounted on the train's undercarriage, allowing the train to levitate between 0.39 and 3.93 inches (1 to 10 cm) above the guideway. However, some form of support is needed for taking off and landing, since the EDS cannot be levitated at speeds lower than 62 mph. The second design is called ElectroMagnetic Suspension (EMS). The German technology, the Transrapid International (TRI) maglev system, is based on an EMS design, which is an attractive force levitation system. Electronically controlled support magnets are located on both sides along the entire length of the vehicle. Ferromagnetic stator packs are mounted to the underside of the guideway. The electromagnets on the vehicle interact with and are attracted to ferromagnetic rails on the guideway. Electromagnets attached to the train's undercarriage are directed up toward the guideway, which levitates the train about 1/3 inch (1 cm) above the guideway and keeps the train levitated even when it's not moving. The attractive force produces inherently unstable vehicle support because the attractive force increases as the vehicle/guideway gap decreases. An electronic control system is equipped to maintain the vehicle/guideway gap and prevent contact. This involves the complex problems of gap sensing, analog and digital control, and precision construction. Guidance magnets are located on both sides along the entire length of the vehicle to keep the vehicle laterally stable during travel on the track. Electronic control systems control the clearance (nominally 10 mm). The levitation system uses on-board batteries that are independent of the propulsion system. The vehicle is capable of hovering up to one hour without external energy. While traveling, the on-board batteries are recharged by linear generators integrated into the support magnets. A synchronous, long stator linear motor is used in the Transrapid maglev system both for propulsion and braking. It functions like a rotating electric motor whose stator is cut open and stretched along under the guideway. Inside the motor windings, alternating current is generating a magnetic traveling field that moves the vehicle without contact. The support magnets in the vehicle function as the excitation portion (rotor). The speed can be continuously regulated by varying the frequency of the alternating current. If the direction of the traveling field is reversed, the motor becomes a generator which brakes the vehicle without any contact. Figure 1.5 schematically shows that, in accordance with Lenz’s Law, the interaction of the levitation field with the current in the slots of the rail results in propulsion or braking force. During the motion of the magnet along the rail, the linear generator winding of the main pole is coupled with a non-constant flux, which induces a voltage and reloads the on-board batteries. The generation process begins in the range of 15 km/h and equals the losses of the magnetic suspension systems at 90 km/h. The whole energy losses of the vehicle are compensated at a velocity of 110 km/h and the batteries are reloaded. Thus the levitation magnet integrates three tasks: levitation, propulsion and transfer of energy to the vehicle. The maglev train hovers over a double track guideway. It can be mounted either at-grade or elevated on columns and consists of individual steel or concrete beams. One major difference between Japanese and German maglev trains is that the Japanese trains use super-cooled, superconducting electromagnets. In the EMS system, which uses standard electromagnets, the coils only conduct electricity when a power supply is present. But the technical requirements for Japanese maglev train are higher than in the case of attractive magnetic forces for which only one side of the system needs to be equipped with electrical wires (the vehicle) for vehicle levitation. Another difference between the systems is that the Japanese trains levitate nearly 4 inches (10 cm) above the guideway. Compared with German trains, which are levitated only about 1/3 inch (1cm), this great gap will generate high stray magnetic fields. Since the gap is much smaller in the EMS system, the force density is sufficiently high and the power consumption is very low even with ordinary electromagnets. It is not necessary to use superconducting coils. While levitation can be achieved at low speed and even at standstill for an EMS system, maglev trains using EDS system must roll on rubber tires until they reach a lift-off speed of about 62 mph (100 kph). Maglev Progress Germany (TRI) has been investigating electromagnetic levitation since 1969, and commissioned the TR02 in 1971. The eighth generation vehicle, the TR08, which operates on 19.6 miles (31.5km) of guideway at the Emsland test track in northwest Germany, is the culmination of nearly 30 years of German maglev development. Control systems regulate levitation and guidance forces to maintain a 1cm (0.4in) gap between the magnets and the iron tracks on the guideway. Some of its precursor prototype vehicles, the TR07 and the TR06, have been tested at the Transrapid Test Facility (TVE) for more than 15 years. Construction work of the Shanghai Transrapid line began in March 2001. After only 22 months of construction time, the world's first commercially operated Transrapid train made its successful maiden trip on December, 31 2002. On December 29, 2003, the world’s first commercial Transrapid line with a five section train started scheduled operation in Shanghai. The Shanghai maglev system travels on a 30km double-track elevated guideway, connecting LongYang Station in Shanghai to Pudong International Airport. The journey time is under 8 minutes. Regardless of the load and speed, the onboard control system maintains a 10mm gap with a ±2mm tolerance between the vehicle’s support magnets and the guideway’s stators and between the guidance magnets and the steel guide rails. A hybrid girder design is used to combine the low cost of concrete with the precision manufacturing offered by steel. The I-shaped hybrid girder is 25m long, 2.8 wide, 2.2m high and weighs 1.86MN with a reinforced concrete center girder and bolted steel cantilevers. The girders were milled to a precision of 0.2mm.. Engineers evaluated the girder with respect to as many as 14,000 load cases by consideration of the deflection, dynamic strength and thermal expansion. The reinforced concrete support piers are designed to withstand the seismic forces of earthquakes up to 7.5 on the Richter scale. The maximum allowable total deformation of the guideway is 10mm, which can come from the settlements caused by consolidation or creep, by dead load, by cyclic loads from the vehicles or by dynamic loads during operation. "Three-way" bearings are installed between the guideways to allow alignment corrections. The Chinese government intends to link Shanghai to the city of Hangzhou, 193km to the southwest, which would create the world’s first intercity maglev line. In Germany, starting in 2009, the Transrapid will connect Munich's city center with "Franz-Josef Strauß" Airport. The construction of the Shanghai Transrapid line and the decision on the maglev projects in Germany have given credibility to the innovative rail system. In the U.S., Congress established the Maglev Deployment Program in 1998 as part of the Transportation Equity Act for the 21st Century (TEA-21) with the expressed purpose of building a maglev demonstration project. Six projects are about to be decided on: a 60 kilometer long connection between Baltimore and Washington, a 76 kilometer long airport link in Pittsburgh, two in Southern California, one from Las Vegas to Anaheim, California, and one from Atlanta to Chattanooga, Tennessee. [Source: Huiguang Dai, “Dynamic Behavior of Maglev Vehicle/Guideway System with Control”, Department of Civil Engineering Case Western Reserve University, August, 2005.]
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