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The desire to develop an efficient means of mass transit and the congestion in airports are pointed the main reason behind the birth of Maglev trains. Maglev (magnetic levitation) has been described as the brightest form of mass transit.
Despite the fact that this new form of mass transit commenced operations between Birmingham airport and the main railway in 1984, research on Maglev trains began as early as 1934 by Herman Kemper of Germany in 1934. This new development in mass transport generated interest in a number of countries such as Japan, the United States and china.
The levitation and propulsion of Maglev trains are based on the principles of electromagnetism. The advantage of the car over all forms of transport is that it has no contact with the rail, thus moves without friction. This enables Maglev trains to attain very high speeds of almost 500 kilometres per hour.
Furthermore, the cars have no engines or any moving parts, despite the fact that they need a lot of electricity to create the desired powerful electromagnets on the tracks. According to Hillebrand (2008), “the basic principle applied in maglev trains is that of the magnetic poles, where like poles repel while unlike poles attract.”
Working Principle of Maglev Trains
These trains are called Maglev trains because of the fundamental concepts under which they work. These cars are fitted with huge magnets that move above their tracks, reducing the impact of friction and enabling the cars to attain much higher speeds than conventional trains.
The trains’ powerful attached magnets are used to create a high density of magnetic field at the bottom. The tracks have electromagnetic magnetic field that repels this magnetic density on the bottom, thereby propelling the car forward. The magnets are U-shaped and fitted with individual coils to which an alternating current is applied in order to create repulsion between magnets.
The gap between the train and the trucks is about 2 and 3 cm for Indatruck models, or 1 cm for Transrapid International model. Meissner effect is used to create bearings without the train coming into contact with the trucks. Thus, the train can climb steep hills or even ice-covered trucks without losing speed considerably.
Hillebrand (2008) argues that these trains tend to quite pricey compared to conventional trains. Other developments introduced another set of coils in which alternating current passes to create electromagnets. Two sets of coils achieved the function of checking the lateral movement, while the other levitated the car. This is done by placing guidance magnets on the left side so that the train moves forward and does not hit the sides.
Electromagnetic Suspension (EMS)
This is one of the most efficient forms of Maglev cars. In this type of Maglev technology, the train levitates above the steel rail while electromagnets that are strategically attached t the train are placed below.
According to Hillebrand (2008), “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 and the rail is situated between the upper and lower edges.
To create large magnetic fields, superconductors are used to produce stronger magnetic fields. Research in this filed has indicated that stronger magnetic fields are produced by rare earth magnets, other than iron and ferrite. Neodymium-iron-boron is used to create the desired high magnetic field.
Levitation of the train
The suspension or levitation of EDS is as a result of the magnetic fields that bombard the car as it passes through the superconducting magnets.
According to Oxlade (2006), “the electromagnets underneath are attracted to the track, made of a ferromagnetic substance (i.e., a regular magnet made of something similar to iron), and just enough energy is put into the electromagnets to keep the vehicle hovering around the track.” Once the car is levitated from the track, a complex system of feedback is used to maintain the train at an appropriate distance from the track. The figure below illustrates how levitation is achieved in EDS
Oxlade (2006, p. 17).
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Propulsion of the Train
The propulsion if the train takes place after it is levitated by the repulsion of magnetic forces. The truck has several coils which use alternating current to change polarity at a high frequency. The change of polarity by the coils makes them propel forward.
Vertical magnetic forces that provide levitation make the car to balance in suspension and is stabilized by the horizontal magnetic forces so that the car is centred and does not drift to any side. Gibilisco (2006) points out that “the frequency of the alternating current is synchronized to match the speed of the train and the offset between the field exerted by magnets on the train and the applied field creates a force moving the train forward.”
Higher levitation speeds were achieved in the Japanese models by positioning upper and lower coils, such that they created field currents of figure of eight. This arrangement is called Halbach array whose main purpose is concentration of magnetic field above the car. While the lower coils produced repulsive forces for levitating the train, the lower coils provided the “push-pull effect” together with linear motors in the tracks which propel the car forward at higher.
Stopping a Maglev Train
The pulling up of the train along the railway track involves a linear synchronous motor (LSM), which makes use of electromagnetic currents in the car to head. This enables the car to be continually and continuously drawn further along its track. The process of stopping a Maglev car involves reducing the frequency of the electromagnetic fields pulling the vehicle. This is because these cars are propelled by the power of the magnetic fields that are directly proportional to the frequency of the of the electromagnetic fields pulling the vehicle.
The train has other features that make it to be safe, given that some can reach high speeds of 581 km/h. Electric power is used to accelerate the train until full levitation is reached. The reason to use the superconductors, besides the high magnetic field potential, is that they can retain this field for some time even after power failure.
Power can fail, and modern maglev trains have auxiliary wheels that help them decelerate until they stop. Computers are used to monitor levitation distance to ensure the speeds and movements are safe so that in case of any anomaly, the train is automatically halted and corrective actions are taken. Some models have batteries for electricity back up in case power supply is interrupted.
There is very small between the models of producing motion in the maglev trains, although depending on the arrangement of electromagnetic coils and force that is used to provide first acceleration, top speeds attainable can vary. For example, maglev trains that are based on Electrodynamics Suspension (EDS) use rubber wheels for the first 100 km/h after which coils are activated and move by levitation propulsion after which they can reach top speeds of 522 km/h.
Gibilisco, S. 2006. Alternative energy demystified. New York: McGraw-Hill Professional.
Hillebrand, J. 2008. The Magnetic Levitation Train: A Technology Ahead of Its Time? Hamburg: GRIN Verlag.
Oxlade, C. 2006. Trains. New York: Black Rabbit Books.