14-07-2012, 12:30 PM
MAGLEV TRAINS
MAGLEV TRAINS.doc (Size: 712.5 KB / Downloads: 135)
INTRODUCTION
WHAT ARE MAGLEV TRAINS?
Have you heard of maglev trains? Well these are going to be the trains of the 21st century. They are high-speed trains running in Japan and Germany. The speed of a normal Indian trains is much less than 60 km/hour, where as a maglev train is expected to go as fast as 400 km/hour! This will revolutionize the way people travel, in the near future. Maglev stands for magnetic levitation. Maglev trains function on the principles of magnets.
A substance that attracts another substance is known as a magnet. Mankind has known permanent magnets like loadstones, since thousands of years. These days magnets can be made from alloys of elements like iron, nickel, samarium, cobalt, tin, niobium, etc. All of us are familiar with a magnetic compass needle. This instrument has a small magnet, which deflects and shows the north-south directions.
Any magnet has two poles : the north pole and the south pole. Two like poles attract each other and two unlike poles repel each other. This means that when two magnets are brought close together, and if their N poles face each other, the magnets will be repelled. On the other hand if the N pole of one magnet is brought close to the S pole of the second magnet, the two magnets will get attracted together.
When a magnet is kept at one place, it influences its surrounding. If you take a bar magnet on a piece of paper and sprinkle some iron filings, you will notice that the iron filings form a particular pattern around the magnet. The pattern is called the magnetic lines of force. The effect the magnet has around its surrounding is called the magnetic field.
These days electromagnets are used everywhere. When electric current is passed through a circular coil, a magnetic field is produced. Take a wire and connect it to a battery and a key. Keep a compass needle in the centre. Note its initial position. As soon as you pass a current through the wire, the compass needle will show a deflection. As long as the current is passing through the wire, the compass needle will stay deflected. This clearly demonstrates that an electric current induces magnetic field around itself. Reverse the current, the deflection of the needle will be in the opposite direction. Thus electromagnets can be constructed easily. Also its magnetic poles can be reversed by reversing the direction of flow of the current.
In a maglev train, a series of electromagnets are placed at the bottom of the train and sides of the tracks. The maglev trains are pushed and speeded up by the fact that like poles attract and unlike poles repel. The strength of attraction and repulsion depends on the current. The speed of the train is determined by how fast the currents can be reversed. The train is virtually levitating from the tracks or the ground. The levitation arises due to repulsion of like poles. The train glides frictionless along the tracks, as there is no physical contact with the track. The trains are generally levitating a few inches above the ground.
In ordinary trains, the friction of the wheels with the tracks puts a restriction on the amount of speed the train can reach. Since there is no physical contact between the tracks and the train, the ride in this train is smooth, without any noise and fast. The speed is obtained due to attraction of unlike poles. The magnets are positioned in such a precise well aligned way, that one pair of electromagnets is in an attractive mode and the immediate pair is in the repulsive mode. The switching or reversing the current in the electromagnets propels the train forward. The rate of this switching determined the speed of the train.
When the train has to halt, the current through the electromagnets is switched off (this makes the magnetic fields zero) and a set of wheels is lowered so that the friction between the tracks and the wheels brings the train to a halt.
FROM STEAM TO MAGLEV:
Today, new technology has resulted in faster, more efficient trains that consume less energy than ever before. For almost 150 years, locomotives burned wood, coal, or oil to create steam. The steam was then injected into cylinders to create pressure to drive the pistons; the spent steam was exhausted upwards through the stack and also created a draft to bring oxygen into the firebox. Steam-powered locomotives required massive amounts of water and fuel -- either coal or wood -- consuming four times as much water as fuel. As the railroads began searching for an alternative to the steam locomotive at the turn of the century, they turned to electrical power. Electric locomotives were clean (important because of new air pollution ordinances) and powerful. These trains could convert electrical energy from an outside power source directly into mechanical energy, resulting in smooth torque, almost instantaneous, unlimited power (important for climbing hills), and eliminating the need to carry fuel on board
PRINCIPLE OF MAGLEV
Maglev is a system in which the vehicle runs levitated from the guideway (corresponding to the rail tracks of conventional railways) by using electromagnetic forces between superconducting magnets on board the vehicle and coils on the ground. The following is a general explanation of the principle of Maglev.
Principle of magnetic levitation:
.
The figured levitation coils are installed on the sidewalls of the guideway. When the on-board superconducting magnets pass at a high speed about several centimeters below the center of these coils, an electric current is induced within the coils, which then act as electromagnets temporarily. As a result, there are forces which push the superconducting magnet upwards and ones which pull them upwards simultaneously, thereby levitating the Maglev vehicle
Principle of propulsion:
A repulsive force and an attractive force induced between the magnets are used to propel the vehicle (superconducting magnet). The propulsion coils located on the sidewalls on both sides of the guideway are energized by a three-phase alternating current from a substation, creating a shifting magnetic field on the guideway. The on-board superconducting magnets are attracted and pushed by the shifting field, propelling the Maglev vehicle.