ABSTRACT:-
This Project was undertaken to briefly explain the Maglev, or magnetic levitation, which is a system of transportation that suspends, guides and propels vehicles, predominantly trains, using magnetic levitation from a very large number of magnets for lift and propulsion.
In this Project I have tried to explain about Functionality of Maglev and its Application.
I have briefly described about different types of maglev technology and its comparison with normal trains with few advantages and portrayed few Maglev trains running in Japan and Germany.
CONTENTS
Ø Introduction
Ø How Maglev train works
Ø Types of Maglev Trains
Ø Applications of Maglev
· Leviation
Methods of leviation
· Propulsion
· Evacuated tubes
· Stability
· Transrapid
· Lateral guidence
Ø Comparison of Maglev and conventional trains
Ø Some Maglev Trains
Ø Advantages
Ø Conclusion
Ø References
INTRODUCTION
Maglev, or magnetic levitation, is a system of transportation that suspends, guides and propels vehicles, predominantly trains, using magnetic levitation from a very large number of magnets for lift and propulsion. This method has the potential to be faster, quieter and smoother than wheeled mass transit systems. The power needed for levitation is usually not a particularly large percentage of the overall consumption; most of the power used is needed to overcome air drag, as with any other high speed train.
The highest recorded speed of a Maglev train is 581 kilometres per hour (361 mph), achieved in Japan in 2003, 6 kilometres per hour (3.7 mph) faster than the conventional TGV speed record.
The first commercial Maglev "people-mover" was officially opened in 1984 in Birmingham, England. It operated on an elevated 600-metre (2,000 ft) section of monorail track between Birmingham International Airport and Birmingham International railway station, running at speeds up to 42 km/h (26 mph); the system was eventually closed in 1995 due to reliability and design problems.
• A few countries are using powerful electromagnets to develop high-speed trains, called maglev trains.
• Traveling at speeds of up to 310 mph (500 kph), maglev trains could begin connecting distant cities in a few years.
The principal of a Magnet train is that floats on a magnetic field and is propelled by a linear induction motor. They follow guidance tracks with magnets. These trains are often refered to as Magnetically Levitated trains which is abbreviated to MagLev. Although maglevs don't use steel wheel on steel rail usually associated with trains, the dictionary definition of a train is a long line of vehicles travelling in the same direction - it is a train.
HOW MAGLEV WORKS:-
• A maglev train floats about 10mm above the guide way on a magnetic field.
• It is propelled by the guide way itself rather than an onboard engine by changing magnetic fields.
• Electromagnets on track: they attract the train as it is coming, and repel it as it’s going
• Once the train is pulled into the next section the magnetism switches so that the train is pulled on again
• The Electro-magnets run the length of the guide way.
TYPES OF MAGLEV TECHNOLOGY
There are notably three main technologies of maglev:-
1. Electromagnetic suspension (EMS) [electromagnets in the train attract it to a magnetically conductive (usually steel) track.]
In current electromagnetic suspension (EMS) systems, the train levitates above a steel rail while electromagnets, attached to the train, are oriented toward the rail from below. The system is typically arranged on a series of C-shaped arms, with the upper portion of the arm attached to the vehicle, and the lower inside edge containing the magnets. The rail is situated between the upper and lower edges.
The separation between the vehicle and the guideway must be constantly monitored and corrected by computer systems to avoid collision due to the unstable nature of electromagnetic attraction; due to the system's inherent instability and the required constant corrections by outside systems, vibration issues may occur.
The major advantage to suspended maglev systems is that they work at all speeds, unlike electrodynamic systems which only work at a minimum speed of about 30 km/h. This eliminates the need for a separate low-speed suspension system, and can simplify the track layout as a result.
2. Electrodynamic suspension (EDS)
[uses electromagnets on both track and train to push the train away from the rail.]
In electrodynamic suspension (EDS), both the rail and the train exert a magnetic field, and the train is levitated by the repulsive force between these magnetic fields. The magnetic field in the train is produced by either electromagnets or by an array of permanent magnets. The repulsive force in the track is created by an induced magnetic field in wires or other conducting strips in the track. A major advantage of the repulsive maglev systems is that they are naturally stable - minor narrowing in distance between the track and the magnets create strong forces to repel the magnets back to their original position, while a slight increase in distance greatly reduced the force and again returns the vehicle to the right separation. No feedback control is needed.
Strong magnetic fields onboard the train would make the train inaccessible to passengers with pacemakers or magnetic data storage media such as hard drives and credit cards, necessitating the use of magnetic shielding; limitations on guideway inductivity limit the maximum speed of the vehicle; vehicle must be wheeled for travel at low speeds.
The drag force can be used to the electrodynamic system's advantage, however, as it creates a varying force in the rails that can be used as a reactionary system to drive the train, without the need for a separate reaction plate, as in most linear motor systems.
Another experimental technology, which was designed, proven mathematically, colleague reviewed, and patented, but is yet to be built, is the magnetodynamic suspension (MDS), which uses the attractive magnetic force of a permanent magnet array near a steel track to lift the train and hold it in place. It is also called the Inductrack system or the permanent magnet system.
The major advantage of this technology is that it provides Failsafe Suspension - no power required to activate magnets; Magnetic field is localized below the vehicle; can generate enough force at low speeds (around 5 km/h) to levitate maglev train and in case of power failure vehicles slow down on their own safely.
But this technology also has its drawback. It requires either wheels or track segments that move for when the vehicle is stopped. Magnetodynamic system is a new technology that is still under development (as of 2008) and as yet has no commercial version or full scale system prototype.
APPLICATIONS OF MEGLEV:-
Levitation
• The passing of the superconducting magnets by figure eight levitation coils on the side of the tract induces a current in the coils and creates a magnetic field. This pushes the train upward so that it can levitate 10 cm above the track.
• The train does not levitate until it reaches 50 mph, so it is equipped with retractable wheels.
LEVIATION METHODS:-
• Electromagnetic levitation:-
Electromagnetic levitation (EML), patented by Muck in 1923, is one of the oldest levitation techniques used for containerless experiments. The technique enables the levitation of an object using electromagnetic radiation. A typical EML coil has reversed winding of upper and lower sections energized by an Radio frequency power supply.
•Electrostatic levitation:-
Electrostatic levitation is the process of using an electric field to levitate a charged object and counteract the effects of gravity. It was used, for instance, in Robert Millikan's oil drop experiment and is used to suspend the gyroscopes in Gravity Probe B during launch.
Due to Earnshaw's theorem no static arrangement of classical electrostatic fields can be used to stably levitate a point charge. There is a point where the two fields cancel, but it is unstable. By providing feedback it is possible to adjust the charges to achieve a quasi static levitation.
In electrostatic levitation an electric field is used to counteract gravitational force.
•Acoustic leviation:-
Acoustic levitation is a method for suspending matter in a medium by using acoustic radiation pressure from intense sound waves in the medium. Acoustic levitation is possible because of the non-linear effects of intense sound waves.
Some methods can levitate objects without creating sound heard by the human ear such as the one demonstrated at Otsuka Lab, while others produce some audible sound. There are many ways of creating this effect, from creating a wave underneath the object and reflecting it back to its source, to using an acrylic glass tank to create a large acoustic field.
Acoustic levitation is usually used for containerless processing which has become more important of late due to the small size and resistance of microchips and other such things in industry. Containerless processing may also be used for applications requiring very-high-purity materials or chemical reactions too rigorous to happen in a container. This method is harder to control than other methods of containerless processing such as electromagnetic levitation but has the advantage of being able to levitate nonconducting materials.
Casimir effect :-
The Casimir effect and the Casimir-Polder force are physical forces arising from a quantized field. The typical example is of two uncharged metallic plates in a vacuum, placed a few micrometers apart, without any external electromagnetic field. In a classical description, the lack of an external field also means that there is no field between the plates, and no force would be measured between them. When this field is instead studied using quantum electrodynamics, it is seen that the plates do affect the virtual photons which constitute the field, and generate a net force—either an attraction or a repulsion depending on the specific arrangement of the two plates. Although the Casimir effect can be expressed in terms of virtual particles interacting with the objects, it is best described and more easily calculated in terms of the zero-point energy of a quantized field in the intervening space between the objects. This force has been measured, and is a striking example of an effect purely due to second quantization. However, the treatment of boundary conditions in these calculations has led to some controversy. In fact " Casimir's original goal was to compute the van der Waals force between polarizable molecules" of the metallic plates. Thus it can be interpreted without any reference to the zero-point energy (vacuum energy) or virtual particles of quantum fields.
PROPULSION:-
• An alternating current is ran through electromagnet coils on the guide walls of the guide way. This creates a magnetic field that attracts and repels the superconducting magnets on the train and propels the train forward.
• Braking is accomplished by sending an alternating current in the reverse direction so that it is slowed by attractive and repulsive forces.
In electrodynamic suspension (EDS), both the rail and the train exert a magnetic field, and the train is levitated by the repulsive force between these magnetic fields. The magnetic field in the train is produced by either electromagnets or by an array of permanent magnets . The repulsive force in the track is created by an induced magnetic field in wires or other conducting strips in the track. A major advantage of the repulsive maglev systems is that they are naturally stable - minor narrowing in distance between the track and the magnets create strong forces to repel the magnets back to their original position, while a slight increase in distance greatly reduced the force and again returns the vehicle to the right separation.] No feedback control is needed.
The drag force can be used to the electrodynamic system's advantage, however, as it creates a varying force in the rails that can be used as a reactionary system to drive the train, without the need for a separate reaction plate, as in most linear motor systems. Laithwaite led development of such "traverse-flux" systems at his Imperial College lab. Alternately, propulsion coils on the guideway are used to exert a force on the magnets in the train and make the train move forward. The propulsion coils that exert a force on the train are effectively a linear motor: an alternating current flowing through the coils generates a continuously varying magnetic field that moves forward along the track. The frequency of the alternating current is synchronized to match the speed of the train. The offset between the field exerted by magnets on the train and the applied field creates a force moving the train forward.
EVACUATED TUBES:-
Some systems (notably the swissmetro system) propose the use of vactrains — evacuated (airless) tubes used in tandem with maglev technology to minimize air drag. This has the potential to increase speed and efficiency greatly, as most of the energy for conventional Maglev trains is lost in air drag.
One potential risk for passengers of trains operating in evacuated tubes is that they could be exposed to the risk of cabin depressurization unless tunnel safety monitoring systems can repressurize the tube in the event of a train malfunction or accident.
STABILITY:-
Earnshaw's theorem shows that any combination of static magnets cannot be in a stable equilibrium. However, the various levitation systems achieve stable levitation by violating the assumptions of Earnshaw's theorem. Earnshaw's theorem assumes that the magnets are static and unchanging in field strength and that the relative permeability is constant and greater than 1 everywhere. EMS systems rely on active electronic stabilization. Such systems constantly measure the bearing distance and adjust the electromagnet current accordingly. All EDS systems are moving systems (no EDS system can levitate the train unless it is in motion).
Because Maglev vehicles essentially fly, stabilisation of pitch, roll and yaw is required by magnetic technology. In addition translations, surge (forward and backward motions), sway (sideways motion) or heave (up and down motions) can be problematic with some technologies.
TRANSRAPID WORKS
The electromagnets on the underside of the train pull it up to the ferromagnetic stators on the track and levitate the train.
• The magnets on the side keep the train from moving from side to side.
• A computer changes the amount of current to keep the train 1 cm from the track.
• LATERAL GUIDENCE:-
When one side of the train nears the side of the guideway, the super conducting magnet on the train induces a repulsive force from the levitation coils on the side closer to the train and an attractive force from the coils on the farther side. This keeps the train in the center.
COMPARISON OF MAGLEV AND CONVENTIONAL TRAINS:-
• Major comparative differences between the two technologies lie in backward-compatibility, rolling resistance, weight, noise, design constraints, and control systems.
Backwards Compatibility Maglev trains currently in operation are not compatible with conventional track, and therefore require all new infrastructure for their entire route. By contrast conventional high speed trains such as the TGV are able to run at reduced speeds on existing rail infrastructure, thus reducing expenditure where new infrastructure would be particularly expensive (such as the final approaches to city terminals), or on extensions where traffic does not justify new infrastructure.
Efficiency Due to the lack of physical contact between the track and the vehicle, maglev trains experience no rolling resistance, leaving only air resistance and electromagnetic drag, potentially improving power efficiency.
Weight The weight of the large electromagnets in many EMS and EDS designs is a major design issue. A very strong magnetic field is required to levitate a massive train. For this reason one research path is using superconductors to improve the efficiency of the electromagnets, and the energy cost of maintaining the field.
Noise. Because the major source of noise of a maglev train comes from displaced air, maglev trains produce less noise than a conventional train at equivalent speeds. However, the psychoacoustic profile of the maglev may reduce this benefit: A study concluded that maglev noise should be rated like road traffic while conventional trains have a 5-10 dB "bonus" as they are found less annoying at the same loudness level.
Design Comparisons Braking and overhead wire wear have caused problems for the Fastech 360 railed Shinkansen. Maglev would eliminate these issues. Magnet reliability at higher temperatures is a countervailing comparative disadvantage (see suspension types), but new alloys and manufacturing techniques have resulted in magnets that maintain their levitational force at higher temperatures.
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SOME MAGLEV TRAINS
JR-Maglev, Japan
Japan has a demonstration line in Yamanashi prefecture where test trains JR-Maglev MLX01 have reached 581 kilometres per hour (361 mph), slightly faster than any wheeled trains (the current speed record is 574.8 kilometres per hour (357.2 mph).
These trains use superconducting magnets which allow for a larger gap, and repulsive-type electrodynamic suspension (EDS). In comparison Transrapid uses conventional electromagnets and attractive-type electromagnetic suspension (EMS). These "Superconducting Maglev Shinkansen", developed by the Central Japan Railway Company (JR Central) and Kawasaki Heavy Industries, are currently the fastest trains in the world, achieving a record speed of 581 kilometres per hour (361 mph) on December 2, 2003.
Emsland, Germany
Transrapid, a German maglev company, has a test track in Emsland with a total length of 31.5 km (19.6 miles). The single track line runs between Dörpen and Lathen with turning loops at each end. The trains regularly run at up to 420 km/h (260 mph). The construction of the test facility began in 1980 and finished in 1984.
ADVANTAGES:-
Safety
• The trains are virtually impossible to derail because the train is wrapped around the track.
• Collisions between trains are unlikely because computers are controlling the trains movements.
Maintenance
• There is very little maintenance because there is no contact between the parts.
Comfort
• The ride is smooth while not accelerating..
Economic Efficency
• The initial investment is similar to other high speed rail roads. (Maglift is $20-$40 million per mile and I-279 in Pittsburg cost $37 million per mile 17 years ago.)
• Operating expenses are half of that of other railroads.
• A train is composed of sections that each contain 100 seats, and a train can have between 2 and 10 sections.
• The linear generators produce electricity for the cabin of the train.
Speed
• The train can travel at about 300 mph. (Acela can only go 150 mph)
• For trips of distances up to 500 miles its total travel time is equal to a planes (including check in time and travel to airport.)
• It can accelerate to 200 mph in 3 miles, so it is ideal for short jumps. (ICE needs 20 miles to reach 200 mph.)
Envoirnment:-
• It uses less energy than existing transportation systems. For every seat on a 300 km trip with 3 stops, the gasoline used per 100 miles varies with the speed. At 200 km/h it is 1 liter, at 300 km/h it is 1.5 liters and at 400 km/h it is 2 liters. This is 1/3 the energy used by cars and 1/5 the energy used by jets per mile.
• The tracks have less impact on the environment because the elevated models (50ft in the air) allows all animals to pass, low models ( 5-10 ft) allow small animals to pass, they use less land than conventional trains, and they can follow the landscape better than regular trains since it can climb 10% gradients (while other trains can only climb 4 gradients) and can handle tighter turns.
Noise Pollution
• The train makes little noise because it does not touch the track and it has no motor. Therefore, all noise comes from moving air. This sound is equivalent to the noise produced by city traffic.
Magnetic Field:
• The magnetic field created is low, therefore there are no adverse effects.
CONCLUSION:-
This system is not ready for use now, but it should be ready in a few years. It’s top speed with people aboard is 350 mph. The super conducting magnets create a strong magnetic field that could be a problem for some passengers. The train is earthquake proof because the greater space (10 cm) between the track and the train leaves more room for track deformation. Linear generators will produce all the electricity needed in the train’s interior. Only the part of the track that is used will be electrified so no energy is wasted. Maglev trains use magnets to levitate and propel the trains forward. Since there is no friction these trains can reach high speeds. It is a safe and efficient way to travel. Governments have mixed feelings about the technology. Some countries, like China, have embraced it and others like Germany have balked at the expense.
REFERENCES:-
Ø “How Maglev Trains Work”. http://travel.howstuffworks.com/maglev-train.htm
Ø Maglevs (Magnetically Levitated Trains)”. http://www.okeating.com/hsr/maglev.htm
Ø “Electromagnetic Systems”. http://www.ga.com/atg/ems.php
Ø "MagLev: A New Approach". http://www.skytran.net/press/sciam01.htm.
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