30-07-2012, 10:59 AM
A Technical Paper on Magnetic Levitation
[attachment=29454]
ABSTRACT
This paper “A technical paper on magnetic levitation”deals with the present scenario of magnetic levitation (maglev) with Linear induction motor(LIM) .The magnetically levitated train has no wheels, but floats-- or surfs-- on an electromagnetic wave, enabling rides at 330 miles per hour. By employing no wheels, maglev eliminates the friction, and concomitant heat, associated with conventional wheel-on-rail train configurations. There are two basic types of non-contact Maglev systems Electro Dynamic Suspension (EDS), and Electro Magnetic Suspension (EMS). EDS is commonly known as "Repulsive Levitation," and EMS is commonly known as "Attractive Levitation”. Each type of Maglev system requires “propulsion” as well as "levitation." The various projects use different techniques for propulsion, but they are all variations of the Linear Induction Motor (LIM) or Linear Synchronous Motor (LSM).The conversion to a linear geometry has a far greater effect on induction motor performance than on that of synchronous motors.The cost of making the guide way is a high percentage of the total investment for a maglev system. The comparison looks even better for maglev when the terrain becomes difficult. Many of the tunnels, embankments, and cuttings necessary for roads and railroads are avoided because maglev guide ways can be easily adapted to the topography. The Maglev system requires a slightly larger start-up capital construction cost, but its operating cost can be one-half that of conventional rail because it deploys electricity in electromagnets in an extraordinarily efficient manner, rather than using as a fuel source coal, gas or oil. The crucial point is that maglev will set off a transportation and broader scientific explosion.
INTRODUCTION
Air flights are and will remain beyond the reach of a major section of society, particularly in India. Moreover there are problems of wastage of time in air traffic delays and growing safety concerns. Trends in increased mobility of large masses with changing lifestyle for more comfort are leading to congestion on roads with automobiles. Besides, increasing pollution levels from automobiles, depleting fuel resources, critical dependence on the fuel import and due to a limited range of mobility of buses and cars the need for fast and unwavering transportation is increasing throughout the world. High-speed rail has been the solution for many countries. Trains are fast, comfortable, and energy-efficient and magnetic levitation may be an even better solution.Development of magnetic levitated transport systems is under progress in developed countries and it is just a matter of time they make inroads to India as well. Therefore, it will be interesting to know about the science and technology behind mass ground transport system known as "magnetic flight".
MAGNETIC LEVITATION
Magnetic levitation is the use of magnetic fields to levitate a (usually) metallic object. Manipulating magnetic fields and controlling their forces can levitate an object. In this process an object is suspended above another with no other support but magnetic fields. The electromagnetic force is used to counteract the effects of gravitation. . The forces acting on an object in any combination of gravitational, electrostatic, and magneto static fields will make the object's position unstable. The reason a permanent magnet suspended above another magnet is unstable is because the levitated magnet will easily overturn and the force will become attractive. If the levitated magnet is rotated, the gyroscopic forces can prevent the magnet from overturning. Several possibilities exist to make levitation viable. It is possible to levitate superconductors and other diamagnetic materials, which magnetize in the opposite sense to a magnetic field in which they are placed. A superconductor is perfectly diamagnetic which means it expel a magnetic field (Meissner-Ochsenfeld effect). Other diamagnetic materials are common place and can also be levitated in a magnetic field if it is strong enough.
LEVITATION
Each type of Maglev system requires propulsion as well as "levitation." The various projects below use different techniques for propulsion. The first thing a maglev system must do is get off the ground, and then stay suspended off the ground. This is achieved by the electromagnetic levitation system.
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 rail, and the electromagnet switched on, there is attraction, and the levitation electromagnets, which are below the rail, rise up to meet the rail. The car levitates.
LINEAR INDUCTION MOTORS:
LIM's do indeed have two distinct advantages. First of all, they are simpler and less costly to construct. The stationary element of the motor consists of nothing more than a rail or plate of a conducting material, such as aluminum. Alternating current applied to the coils of the moving electromagnets induces a fluctuating magnetic field around this conductor which provides the propulsive force. By contrast, LSM's require the installation of alternating north and south magnetic poles on both moving and stationary elements. Secondly, LIM's are self-starting, with the speed of motion being infinitely variable from zero up to the design maximum. LSM's, on the other hand, exhibit no starting torque; rotary motors of this type are generally equipped with auxiliary squirrel-cage windings so that they can act as induction motors until they reach operating speed.
LINEAR SYNCHRONOUS MOTORS
LSM's possess other advantages, however, which are more than sufficient to outweigh these faults. They are far more efficient; models have been built with efficiencies of 97% or more, whereas the highest value yet attained for an LIM scarcely exceeds 70%. This is true despite the fact that rotary synchronous motors enjoy only a slight efficiency advantage over rotary induction motors; apparently the conversion to a linear geometry has a far greater effect on induction motor performance than on that of synchronous motors. Moreover, the efficiency of an LSM is relatively unaffected by the speed of travel; LIM's, on the other hand, do not reach peak efficiencies until they attain velocities which are well beyond those being considered here.
An LSM also operates at a constant speed, which depends solely on the frequency of the alternating current applied to its armature. This feature offers opportunities for absolute speed control; under normal operation, there is no way for any moving conveyance to alter its prescribed position relative to that of any other vehicle on the track.
CONCLUSION
The Maglev Train: Research on this ‘dream train’ has been going on for the last 30 odd years in various parts of the world. The chief advantages of this type of train are: 1. Non-contact and non-wearing propulsion, independent of friction, no mechanical components like wheel, axle. Maintenance costs decrease. Low noise emission and vibrations at all speeds (again due to non-contact nature). Low specific energy consumption. Faster turnaround times, which means fewer vehicles. All in all, low operating costs. Speeds of up to 500kmph. Low pollutant emissions. Hence environmentally friendly. The Maglev offers a cheap, efficient alternative to the current rail system. A country like India could benefit very much if this were implemented here. Further possible applications need to be explored.
[attachment=29454]
ABSTRACT
This paper “A technical paper on magnetic levitation”deals with the present scenario of magnetic levitation (maglev) with Linear induction motor(LIM) .The magnetically levitated train has no wheels, but floats-- or surfs-- on an electromagnetic wave, enabling rides at 330 miles per hour. By employing no wheels, maglev eliminates the friction, and concomitant heat, associated with conventional wheel-on-rail train configurations. There are two basic types of non-contact Maglev systems Electro Dynamic Suspension (EDS), and Electro Magnetic Suspension (EMS). EDS is commonly known as "Repulsive Levitation," and EMS is commonly known as "Attractive Levitation”. Each type of Maglev system requires “propulsion” as well as "levitation." The various projects use different techniques for propulsion, but they are all variations of the Linear Induction Motor (LIM) or Linear Synchronous Motor (LSM).The conversion to a linear geometry has a far greater effect on induction motor performance than on that of synchronous motors.The cost of making the guide way is a high percentage of the total investment for a maglev system. The comparison looks even better for maglev when the terrain becomes difficult. Many of the tunnels, embankments, and cuttings necessary for roads and railroads are avoided because maglev guide ways can be easily adapted to the topography. The Maglev system requires a slightly larger start-up capital construction cost, but its operating cost can be one-half that of conventional rail because it deploys electricity in electromagnets in an extraordinarily efficient manner, rather than using as a fuel source coal, gas or oil. The crucial point is that maglev will set off a transportation and broader scientific explosion.
INTRODUCTION
Air flights are and will remain beyond the reach of a major section of society, particularly in India. Moreover there are problems of wastage of time in air traffic delays and growing safety concerns. Trends in increased mobility of large masses with changing lifestyle for more comfort are leading to congestion on roads with automobiles. Besides, increasing pollution levels from automobiles, depleting fuel resources, critical dependence on the fuel import and due to a limited range of mobility of buses and cars the need for fast and unwavering transportation is increasing throughout the world. High-speed rail has been the solution for many countries. Trains are fast, comfortable, and energy-efficient and magnetic levitation may be an even better solution.Development of magnetic levitated transport systems is under progress in developed countries and it is just a matter of time they make inroads to India as well. Therefore, it will be interesting to know about the science and technology behind mass ground transport system known as "magnetic flight".
MAGNETIC LEVITATION
Magnetic levitation is the use of magnetic fields to levitate a (usually) metallic object. Manipulating magnetic fields and controlling their forces can levitate an object. In this process an object is suspended above another with no other support but magnetic fields. The electromagnetic force is used to counteract the effects of gravitation. . The forces acting on an object in any combination of gravitational, electrostatic, and magneto static fields will make the object's position unstable. The reason a permanent magnet suspended above another magnet is unstable is because the levitated magnet will easily overturn and the force will become attractive. If the levitated magnet is rotated, the gyroscopic forces can prevent the magnet from overturning. Several possibilities exist to make levitation viable. It is possible to levitate superconductors and other diamagnetic materials, which magnetize in the opposite sense to a magnetic field in which they are placed. A superconductor is perfectly diamagnetic which means it expel a magnetic field (Meissner-Ochsenfeld effect). Other diamagnetic materials are common place and can also be levitated in a magnetic field if it is strong enough.
LEVITATION
Each type of Maglev system requires propulsion as well as "levitation." The various projects below use different techniques for propulsion. The first thing a maglev system must do is get off the ground, and then stay suspended off the ground. This is achieved by the electromagnetic levitation system.
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 rail, and the electromagnet switched on, there is attraction, and the levitation electromagnets, which are below the rail, rise up to meet the rail. The car levitates.
LINEAR INDUCTION MOTORS:
LIM's do indeed have two distinct advantages. First of all, they are simpler and less costly to construct. The stationary element of the motor consists of nothing more than a rail or plate of a conducting material, such as aluminum. Alternating current applied to the coils of the moving electromagnets induces a fluctuating magnetic field around this conductor which provides the propulsive force. By contrast, LSM's require the installation of alternating north and south magnetic poles on both moving and stationary elements. Secondly, LIM's are self-starting, with the speed of motion being infinitely variable from zero up to the design maximum. LSM's, on the other hand, exhibit no starting torque; rotary motors of this type are generally equipped with auxiliary squirrel-cage windings so that they can act as induction motors until they reach operating speed.
LINEAR SYNCHRONOUS MOTORS
LSM's possess other advantages, however, which are more than sufficient to outweigh these faults. They are far more efficient; models have been built with efficiencies of 97% or more, whereas the highest value yet attained for an LIM scarcely exceeds 70%. This is true despite the fact that rotary synchronous motors enjoy only a slight efficiency advantage over rotary induction motors; apparently the conversion to a linear geometry has a far greater effect on induction motor performance than on that of synchronous motors. Moreover, the efficiency of an LSM is relatively unaffected by the speed of travel; LIM's, on the other hand, do not reach peak efficiencies until they attain velocities which are well beyond those being considered here.
An LSM also operates at a constant speed, which depends solely on the frequency of the alternating current applied to its armature. This feature offers opportunities for absolute speed control; under normal operation, there is no way for any moving conveyance to alter its prescribed position relative to that of any other vehicle on the track.
CONCLUSION
The Maglev Train: Research on this ‘dream train’ has been going on for the last 30 odd years in various parts of the world. The chief advantages of this type of train are: 1. Non-contact and non-wearing propulsion, independent of friction, no mechanical components like wheel, axle. Maintenance costs decrease. Low noise emission and vibrations at all speeds (again due to non-contact nature). Low specific energy consumption. Faster turnaround times, which means fewer vehicles. All in all, low operating costs. Speeds of up to 500kmph. Low pollutant emissions. Hence environmentally friendly. The Maglev offers a cheap, efficient alternative to the current rail system. A country like India could benefit very much if this were implemented here. Further possible applications need to be explored.