Maglev Trains. Priyank Malik th Semester Student, Mechanical Engineering

Transcription

1 Maglev Trains Priyank Malik th Semester Student, Mechanical Engineering 5 th Abstract Technical trials on a maglev train track began in Japan in the 1970s, and a speed of 500 kph/310 mph has been reached, with a cruising altitude of 10 cm/4 in. The train is levitated by electromagnets and forward thrust is provided by linear motors aboard the cars, propelling the train along a reaction plate. The German government approved a plan to build the world's first commercial maglev The Berlin- Hamburg line will cost DM8.9 billion ( 3.5 billion). The three-hour journey time will be reduced by a third. Maglev trains in Japan have a 4 inch gap between the train and the track while in motion. When the trains in Japan slow down as they come into the station, wheels underneath the train reattach to the ground eventually bringing the train to a stop. How Maglev trains operate: Japanese Maglev train moves by the force of the magnets. Currently, Maglev trains have been created in Germany and Japan for test runs only. No commercial trains are operating. Germany and Japan are using two different types of maglev trains. Germany is using the power of magnetic "attraction", while Japan is mostly using magnetic "repulsion". In Germany the bottom of Maglev trains wrap around the track leaving only a 3/8 of an inch gap between the train and the track while in motion. In Japan, Maglev trains have magnetic tracks underneath the trains as well as on the sides of the bottom part of the train. The magnets on the side of the track correspond with those on the side of the train while the magnets on the bottom of the track correspond with those underneath the train. The Electrodynamic suspension (EDS) is one method that can be used for maglev trains. Superconductor electromagnets on the train generate a magnetic field. Propulsion coils on the guideway are used to exert a force on these magnets, and make the train move forward. Introduction Did you ever see a train without any wheels? Did you ever think of using magnets to get around? Well, Robert Goddard and a few other scientists did. I'm going to tell you about their invention, the MAGLEV TRAINS. The Magnetic Levitating Train or Maglev Train was first constructed in the 1960's. The Japanese tried to build one in the 1960's but did not have enough knowledge of magnets and it was a glichy experiment. Not until recently did they pick up on their experiment to create the maglev train. Maglev trains have come a long way. It all started with just a few trains in Germany and with one train in Japan. Now the idea has spread. 64 Department of Mechanical & Automobile Engineering

2 There are some in America and many more places. There are many more in Japan and Germany. The fastest is the MLXOI. It has a world record speed of 344 m.p.h. (miles per hour) or 554 kilometers per hour. It takes up no fossil fuels and has virtually no friction. This train is a great deal faster than a conventional train and also has a smoother ride. While most trains have a driver, most of these don't. They can be controlled by a computer. Some computer controlled maglev's are used to get people around airports, state parks, and places like that. This can provide information and perhaps convince the people to create a public maglev train. This train has a lot to do with magnetism and precision. Maglev trains are the future of high speed trains. Maglev combines the benefits of airplanes with the benefits of trains to create "flying trains". Maglev trains use electromagnetic technology to allow trains to actually hover above the ground. With the friction of wheels on rails gone, a whole new era of high speed trains is possible. Tracks for maglev trains are different from those of conventional trains. They are elevated above ground, allowing everything else to go underneath it, and nothing will stand in the way of 300mph trains. Did you ever wonder how maglev's got so fast? It's because the trains hover over a track. The train cars are actually suspended in the air above a single track. They move forward using the repulsive and attractive forces of magnetism. There is no friction to slow the train cars down. Scientists are saying they could get up to 600 to 1000 m.p.h. (966 to 1609 kilometers per hour) in the future with the advance of technology, wow! Now you know a lot about 'the trains of the future,' but I forgot to explain one thing. The word Maglev comes from MAGnetically LEVitated. 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 "8" 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 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 Department of Mechanical & Automobile Engineering 65

3 side near the car and an 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 basic idea behind an electromagnet is extremely simple: By running electric current through a wire, you can create a magnetic field. 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. The repulsion of superconducting magnets and electromagnets in the track keeps a maglev train suspended above the track. By varying the strength and polarity of the track electromagnets, the train can be driven forward. The propulsion coils exert a force on the train in the same way that an electric motor works. An alternating current flowing through the coils causes a continuously varying magnetic field, that moves forward along the track. The magnets on the train line up with this field, and so the train moves. As the train moves forwards, it induces a current in another set of coils, responsible for guidance and levitation of the train. They have a figure of eight shape, and the current flowing through them induces magnetic poles in both the top and bottom halves. These poles ensure that the magnets on the train are repelled by the bottom half, and attracted by the top half, resulting in the train levitating.at slow speeds however, the current induced in these coils or flux is not large enough to support the weight of the train. For this reason the train is fitted with a retractable landing gear to support the train until it takes off. A maglev train floats about 10mm above the guideway on a magnetic field. It is propelled by the guideway itself rather than an onboard engine by changing magnetic fields. 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 guideway. Developing Technology Maglev train technology is a popular topic of transportation conversation in several countries. Germany and Japan are both developing maglev train technology, and both are currently testing prototypes of their trains. (The German company "Transrapid International" also has a train in commercial use -- more about that in the next section.) Although based on similar concepts, the German and Japanese trains have distinct differences. In Germany, engineers have developed an electromagnetic suspension (EMS) system, called Transrapid. In this system, the bottom of the train wraps 66 Department of Mechanical & Automobile Engineering

4 around a steel guideway. Electromagnets attached to the train's undercarriage are directed up toward the guideway, which levitates the train about 1/3 of an inch (1 cm) above the guideway and keeps the train levitated even when it's not moving. Other guidance magnets embedded in the train's body keep it stable during travel. Germany has demonstrated that the Transrapid maglev train can reach 300 mph with people onboard. Japanese engineers are developing a competing version of maglev trains that use an electrodynamic suspension (EDS) system, which is based on the repelling force of magnets. The key difference between Japanese and German maglev trains is that the Japanese trains use supercooled, superconducting electromagnets. This kind of electromagnet can conduct electricity even after the power supply has been shut off. In the EMS system, which uses standard electromagnets, the coils only conduct electricity when a power supply is present. By chilling the coils at frigid temperatures, Japan's system saves energy. Another difference between the systems is that the Japanese trains levitate nearly 4 inches (10 cm) above the guideway. One potential drawback in using the EDS system is that maglev trains must roll on rubber tires until they reach a liftoff speed of about 62 mph (100 kph). Japanese engineers say the wheels are an advantage if a power failure caused a shutdown of the system. Germany's Transrapid train is equipped with an emergency battery power supply. Traverser at the Miyazaki Maglev Test Track as turned toward the curved branch line Curved branch line entry test using MLU002 China test home-made maglev train Are Maglev Trains Safe? Maglev trains have proven to be exceptionally safe, quiet, and fast. Beacause there's no friction with the ground, maglev trains are much more quiet than trucks and automobiles. The only sound caused by the trains is the 'whoosh' as the train goes by from the air friction. Farmers in Germany who have trains running over their fields, when asked about how the feel about the trains running through their farm replied "We don't even know it's there". Cows don't even lift their heads when trains come through at 250mph. Maglev trains are also almost accident free. They are above any obstacles on the ground and are enclosed in or around the track. Also the propulsion system caused by the magnetic fields disallows trains to come to close to other trains on the track. German Maglev goes over farm exceeding 200mph, but is so quiet the cows don't even look up at it. Another issue with maglev trains is whether the magnetic waves, or electromegnetic fields caused by the train will harm the passengers or people living along the lines. Studies have shown that the trains generate minimal magnetic fields, not nearly enough to harm people around the track or any sensitive machinery. The tracks themselves do not generate any electromagnetic fields. The only time the magnetic waves are present is when the trains go by which is only a short time, especially when they go by at Department of Mechanical & Automobile Engineering 67

5 300mph. The magnetic field inside the cabin of the trains is just barely higher than earth's normal magnetic field. So if test runs go alright we could have fast, flying trains operating in the near future. Issues Related to Magnetic Levitating Trains Magnetic Fields Intensity of magnetic field effects of Maglev is extremely low (below everyday household devices) Hair dryer, toaster, or sewing machine produce stronger magnetic fields Energy Consumption Maglev uses 30% less energy than a highspeed train travelling at the same speed. (1/3 more power for the same amount of energy) Noise Levels No noise caused by wheel rolling or engine Maglev noise is lost among general ambient noise At 100m - Maglev produces noise at 69 db At 100m - Typical city center road traffic is 80 db Vibrations Just below human threshold of perception Power Supply 110kV lines fed separately via two substations Power Failure Batteries on board automatically are activated to bring car to next station Batteries charged continuously Fire Resistance of vehicles Latest non-pvc material used that is noncombustible and poor trasmitter of heat Maglev vehicle carries no fuel to increase fire hazard Safety 20 times safer than an airplane 250 times safer than other conventional railways 700 times safer than travel by road Collision is impossible because only sections of the track are activated as needed. The vehicles always travel in synchronization and at the same speed, further reducing the chances of a crash. Operation Costs Virtually no wear. Main cause of mechanical wear is friction. Magnetic levitation requires no contact, and hence no friction. Components normally subjected to mechanical wear are on the whole replaced by electronic comonents which do not suffer any wear Specific energy consumption is less than all other comparable means of transportation. Faster train turnaround time means fewer vehicles The Most Interesting Facts About Maglevs Current speed record is held by MLX01 at the Yamanashi Maglev Test Line: 581 km / h. The possible top speed of Maglev in a vacuum-filled tunnel (no air resistance): km /hr! First approval of a Maglev line: 1996 Germany,, it would have linked Hamburg and Berlin, but the project was cancelled in Department of Mechanical & Automobile Engineering

6 The first official Maglev line: 2004, Shanghai opened line between the airport and the financial district. The lenght of this line is 30km, the possible top speed on this route: 432km / hr. Maglev is an acronym for: Magnetic Levitated. Maglev Suspension Versus Wheeled Suspension Cited advantages of maglev trains over wheeled trains (1, 12) include: 1. Wheels produce medium to high environmental noise levels. 2. Wheeled systems rely on propulsion through wheel-rail friction, and the high aerodynamic drag forces lead to upper speed limits due to limited wheel-rail adhesion. 3. Maglev vehicles can accelerate and decelerate rapidly and bank steeply on curves. 4. Suspension through point contact (up to 70,000 psi or 482 MPa) leads to increased structural requirements and increased wear/maintenance. Frequently Asked Questions How fast can maglev trains travel? As long as the track is straight enough that the train doesn't experience severe accelerations up, down, left, or right, there is no limit to how fast it can go. In fact, the levitation process becomes more and more energy efficient as the speed increases. However, the moving train does experience a pressure drag force (a type of air resistance) that increases roughly as the square of the train's speed. The power needed to overcome this drag force increases as the cube of the train's speed, making it impractical to propel the train forward above a certain speed. What would be a legitimate form of propulsion for magnetic trains? The most sensible propulsion system for a magnetically levitated train would be a linear electric motor. This motor would consist of electromagnets on the train and electromagnets on the track. By turning these electromagnets on and off at carefully chosen moments, they can be used to pull or push the train forward for propulsion or backward for breaking. The timing is important because, for propulsion, the magnet on the train must always be attracted toward the track magnet in front of it and repelled by the track magnet behind it. For breaking, this relationship must be reversed. How does a magnetic train work? How can I make an experiment with it for a school project? There are many techniques for supporting a train on magnetic forces, but the simplest and most promising involves electrodynamic levitation. In this technique, the train has a strong magnet under it and it rides on an aluminum track. The train leaves the station on rubber wheels and then begins to fly on a cushion of magnetic forces when its speed is high enough. Its moving magnet induces electric currents in the aluminum track and these currents are themselves magnetic. The train and track repel one another so strongly with magnetic forces that the train hovers tens of centimeters above the track. To demonstration this effect, you can lower a very strong magnet above a rapidly spinning aluminum disk. In my class, I spin a sturdy aluminum disk with a motor and lower a 5 cm diameter disk magnet onto its surface. I hold the magnet firmly with a strap made of duct tape, so that the magnet won't fly across the room or flip over as it descends. Instead of touching the spinning disk, the magnet floats about 2 cm above it. If you try this experiment, don't spin the aluminum disk too fast or it will tear itself apart. It should spin about as fast as an electric fan on high speed. Also, be careful with the magnet, because it will experience magnetic drag forces as well as the magnetic lift force. If you don't hold tight, it will be yanked out of your hand. For a simpler experiment that anyone can do, float an aluminum pie plate in a basin of water and circle one pole of a strong magnet just above its surface. The pie plate will begin to spin with the magnet. You are again inducing currents in the aluminum, making it magnetic. While the forces here are too weak to lift the magnet in your hand, they are enough to cause the pie plate to begin spinning, even though you never actually Department of Mechanical & Automobile Engineering 69

7 touch it. This technique is used in many electric motors. That's physics for you--the same principles just keep showing up in seemingly different machines. If magnetic trains are to work,, wouldn't friction on the bottom of the train create thermal energy which would destroy the magnetism of the train? When a magnetically levitated train is operating properly, it doesn't touch the track and experiences no friction. In principle, it shouldn't get hot at all. The magnetic drag effect will warm the track slightly, but that won't matter to the train's magnets. Actually, the train's magnets will almost certainly be superconducting wire coils with currents flowing in them. That type of magnet doesn't depend on the magnetic order of permanent magnets. It's the magnetic order of permanent magnets that is destroyed by heat. An electromagnetic coil will stay magnetic as long as current flows through it, even if it's so hot that it's ready to melt. 70 Department of Mechanical & Automobile Engineering