04-07-2014, 10:52 AM
MAGLEV MACHINES
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ABSTRACT
MAGNETIC LEVITATION –It uses magnetic fields to levitate a metallic object .By manipulating magnetic fields and controlling their forces an object can be levitated. Because of the growing need for quicker and more efficient methods for moving people and goods, researchers have turned to a new technique, one using electromagnetic rails and trains. This rail system is referred to as magnetic levitation, or maglev. Maglev is a generic term for any transportation system in which vehicles are suspended and guided by magnetic forces. Instead of engines, maglev vehicles use electromagnetism to levitate (raise) and propel the vehicle. Alternating current creates a magnetic field that pushes and pulls the vehicle which weighs almost about 1500 tonnes and keeps it above the support structure, called a guide way.
INTRODUCTION
The word levitation is derived from a Latin word “LEVIS”, which means light. Magnetic levitation is the use of magnetic fields to levitate a metallic object. By manipulating magnetic fields and controlling their forces an object can be levitated. When the like poles of two permanent magnets come near each other, they produce a mutually repulsing force that grows stronger as the distance between the poles diminishes. When the unlike poles of two permanent magnets are brought close to each other, they produce a mutually attractive force that grows stronger as the distance between them diminish .A levitation system is designed around the attractive force, between unlike poles as it would require a perfect balance between the attractive magnetic force and the suspended weight .In the absence of a perfect lift and weight force profile, the conveyance would either be pulled up toward the magnets or would fall. This simple illustration of magnetic levitation shows that the force of gravity can be counterbalanced by magnetic force.
TYPES OF LEVITATION
There are two ways of levitations,
1. Active 2. Passive.
In an active levitation system, electromagnets are coupled to amplifiers that receive signals from controllers. These controllers process signals from sensors that change the magnetic force to meet the needs of the magnetic system.
Passive magnetic levitation systems are impractical without a stabilizing ingredient. Diamagnetic levitation can be used to add stability to passive levitation systems. The combination of passive and diamagnetic levitation is a functional approach to many magnetic levitation applications
MAGLEV
Powerful electro magnets are used to develop high-speed trains called maglev trains. These will float over a guide way using the basic principles of magnets to replace the old steel wheel and track trains.
Magnetic levitation (maglev) is a relatively new transportation technology in which no contacting vehicles travel safely at speeds of 250 to 300 miles-per-hour or higher while suspended, guided, and propelled above a guide way by magnetic fields. The guide way is the physical structure along which maglev vehicles are levitated. Various guide way configurations, e.g., T-shaped, U-shaped, Y-shaped, and box-beam, made of steel, concrete, or aluminum, have been proposed.
A ultra high-speed transport system with a non-adhesive drive that is independent of wheel-and-rail frictional forces has been a long-standing dream of railway engineers. Maglev, a combination of superconducting magnets and linear motor technology, realizes super high-speed running, safety, reliability, low environmental impact and minimum maintenance
Principle of lateral guidance
The levitation coils facing each other are connected under the guideway, constituting a loop. When a running Maglev vehicle, that is a superconducting magnet, displaces laterally, an electric current is induced in the loop, resulting in a repulsive force acting on the levitation coils of the side near the car and attractive force acting on the levitation coils of the side farther apart from the car. Thus, a running car is always located at the center of the guideway
The Two Principal Systems Are EMS- attractive and EDS-repulsive
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
ELECRODYNAMIC SUSPENSION SYSTEM
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.
You can easily create a small electromagnet yourself by connecting the ends of a copper wire to the positive and negative ends of an AA, C or D-cell battery. This creates a small magnetic field. If you disconnect either end of the wire from the battery, the magnetic field is taken away.
ADVANTAGES OF MAGLEV OVER CONVENTIONAL TRAINS
Conventional trains use an engine where as maglev vehicles instead of engines use electro magnetism to levitate (raise) and propel the vehicle.
Instead of using fossil fuels, the magnetic field created by the electrified coils in the guideway walls and the tracks combine to propel the train.
Using a magnet's repelling force to float above magnets in the guideway, the trains aren't hampered by friction where as, Conventional trains are noisy due to the friction between their wheels and the steel rails, but maglev trains are much quieter.
These maglev trains are incomparable faster than normal conventional trains.
Moreover as these maglev trains work using electromagnetic induction using electricity these are pollution free.
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 turn around times, which mean 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