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Magnetic Levitation Technology: The Maglev Trains.

Maglev-train

Imagine sitting in a warm, cozy, and comfortable place, while flying a few centimeters above the ground. By your side, you see the foggy outlines of the landscape that you are passing by, but you still don’t have a sensation that you’re rushing over 400 km/h.

If that ever happens to you, there are two options: either you are dreaming that you are Aladdin on the magic carpet, either you are having a ride on a Maglev train. You are watching Railways Explained, and, today, we’re talking about Maglev technology. At the begging, we have to say this was a quite challenging topic for us, because of two reasons. The first is the fact that during our education and later work, we did not have many encounters with this kind of transportation. Another is the fact that this topic is very technical and therefore hard to be presented simply and understandably. So, we put some extra effort into research.

Now, let’s begin. The world’s fastest Maglev train achieved an astonishing speed of 603 km/h, which happened in Japan, on the Yamanashi Maglev Line, on April 21st, 2015. But, besides speeds, these trains are super interesting due to the fact, well, they levitate above the ground. Maglev can be defined as the system that enables a train to repel and push up off the track, while at the same time enables the train to move in such elevated condition, taking advantage of the lack of friction. This lack of friction is a direct cause of several advantages that Maglev trains have compared to conventional and high-speed railway systems. Due to the fact, there is no need for moving parts such as wheels and axles, Maglev trains have a longer lifecycle, lower operating costs, higher energy efficiency, and, in the end, they are clean, quieter, and capable of developing much higher speeds. Their main disadvantage is much higher construction cost, which is in some cases 2 or 3 times higher than in the case of a high-speed railway system, and about 60 times higher than in the case of conventional railways. Besides the costs of construction, another factor to be considered is the fact that Maglevs trains require the use of rare-earth elements, which may be quite expensive. The word Maglev itself is a combination of the two words. Magnetic and Levitation.

But, before we take a deep dive, let’s explain how it all begun. The fundamental ideas that led to the creation of Maglev technology started developing already at the beginning of the 20th century. Several different patents and inventions had to be made, to make possible the movement of trains using magnetic levitation. The history of linear electric motors, which are tightly bound to the modern Maglev trains, can be traced back to at least the middle of the 19th century. However, all such models were still too inefficient. It was 1902 and 1907 when the German inventor Alfred Zehden submitted two patents for the first linear-motor-propelled train. Linear motors are a type of electric motors that have their stator and rotor sort of “unrolled”, so instead of producing a rotational movement they produce a linear force along their length. In a linear motor, electrical energy is converted to linear mechanical energy with high efficiency, which is done through the electromagnetic interaction between a coil assembly and a permanent magnet assembly.

Ok, that’s just one piece of the puzzle. In 1908, the Cleveland mayor Tom L. Johnson filed a patent for a “wheel-less high-speed railway” levitated by an induced magnetic field. After that, we had a series of patents for magnetic levitation trains propelled by linear motors, such as those made by Robert Goddard, Emile Bachelet, and Hermann Kemper, during the 1930’ and 1940’. Keep in mind all these were only ideas, drafts, and patents, except for Herman Kemper’s invention, who constructed the first working circuit for hovering on the principle of electromagnetic levitation. However, in the late ‘40s, the British electrical engineer Eric Laithwaite, a professor at Imperial College London, developed the first full-size working model of a linear induction motor. Since, as we indicated, linear motors don’t require physical contact between the vehicle and the guideway, they became a common fixture in the experiments relating to advanced transportation systems. One such project was a so-called Tracked Hovercraft. It was an experimental high-speed train developed in the UK during the 1960s.

It combined two inventions, the hovercraft, and linear induction motor, to produce a train system that would enable 400 km/h passenger service, with lowered capital costs. However, Tracked Hovercraft was canceled as many other similar projects, as part of the budget cuts in 1973. Finally, in the early 1970s, the already mentioned professor, Eric Laithwaite, have discovered something which might be described as the final piece of the Maglev puzzle. In its essence, it was a new and special arrangement of magnets, in science known as the magnetic river. This invention allowed a single linear motor to produce both lift and forward propulsion, allowing a Maglev system to be built with a single set of magnets.

Because of this breakthrough, Dr. Laithwaite became known as “the father of Maglev”. Although Maglevs have been studied and developed for more than half a century since the invention of the Magnetic river, only a few countries today can implement this technology in practice. Furthermore, the only countries that have studied and tested Maglev technology so far are the UK, USA, Japan, Germany, USSR, China, and South Korea. To explain how Maglev works, we must understand some basic concepts of physics. In the first line concepts of attraction and repulsion of magnets, but also the concepts of electromagnetism and superconductivity. Since pretty much everybody understands that the same poles of the magnets oppose, while opposite ones attract each other, we will briefly introduce only the two remaining terms. The first one is electromagnetism, one of the four fundamental forces of nature. What is even more important, the electromagnet is the object which creates a magnetic field when electric current flows through it.

It is usually a simple conductor such as wire or cable, or even better the combination of iron core and a wire wrapped around. The direction of current determines the electromagnet’s polarity and, also, if you change the direction of the current, the poles of the electromagnet will switch. Put that somewhere as a note. Our second term is superconductivity. Superconductivity is a property of the complete disappearance of electrical resistance in various solids as they are cooled below a characteristic temperature. This temperature varies for different materials, but in general, is below 20 K. As superconducting magnets are super strong and super efficient, they are generally used to generate powerful magnetic fields that can levitate and propel the train. Now, Maglevs. There are two main types of Maglev trains. Those based on Electromagnetic suspension, also known as EMS, and those based on Electrodynamic suspension, also known as EDS. Both types have similar propulsion principles, based on the linear motor, while the main difference is in the way how levitation is achieved. Electromagnetic suspension (EMS) uses the attractive force between electromagnets present underside the train and the magnets present on the guideway to levitate the train. This attracting force keeps the train about 1.3 cm above the guideway, bearing in mind it is strong enough to overcome gravitational force. The stabilization of the train is achieved with the help of side, guidance magnets.

The propulsion is secured by constantly changing the polarity of magnets on the track, which, speaking in terms of linear motors, acts as a stator. In that way, the electromagnets onboard, which act as rotor, ‘chase’ the current forward along the track. In that way, the train moves forward, while the speed is controlled by changing the frequency of the alternating current. Having in mind that magnetic attraction varies inversely with the square of the distance, minor changes in distance between the magnets and the rail (suspension gap) can produce greatly varying forces. These changes in force dictated a need for a sophisticated feedback system, which maintain a constant gap of approximately 8–10 mm. This method is simpler to implement than EDS, and it also can maintain levitation at zero speed which is not the case with EDS. Electrodynamic suspension (EDS), on the other side, to levitate the train, uses the repulsive force created between the sets of magnets of the same polarity, which are located on the train and the guideway. This repulsive force is high enough to overcome the gravitational force and allows a train to levitate 10 cm above the guideway. When a train moves along the track, the supercooled, superconducting magnets on either side of the train would induce electric current in the levitation coils and create a magnetic field. Levitation coils are located on the guideway and they have the shape of figure 8.

When those coils experience the changing magnetic field made by the moving superconductors, two currents are induced that opposes the change in the magnetic field. One below that creates a reactive magnetic field that opposes the superconducting magnets pole. And one above that creates a pole that attracts it. Those two combined are responsible for levitation of the vehicle 10 cm above the ground. Propulsion, on the other side, is achieved by a linear synchronous motor, whose “stator” is additional coils in the guideway, while the “rotor” is a superconductor that is already located on the train.

The train is propelled in a similar way like in the case of EMS, by constant changes in the polarity of the trackside magnets. The benefits of this method are incredible stability at high speeds and the ability to maintain the correct distance between the train and the guideway. The bad side is the fact that sufficient speed must be achieved to levitate the train at all.

For this reason, the train must be equipped with wheels or some other form of landing gear to support the train until it reaches take-off speed. Except for the type of suspension, Maglev trains can be divided between low-speed Maglev trains which have a maximum speed of 100–130 km/h, and high-speed Maglev trains having maximum speeds of 400–500 km/h. 6 commercial Maglev systems are currently in operation around the world. China : 3, Japan: 1, South Korea: 2.

Written by Ottay

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