In fact, in the 1950s and 1960s, the railway was once regarded as a sunset transportation industry. Because of the strong challenges from transportation rivals such as aviation and highways, its snail-like crawling speed has become increasingly unsuitable for the rapid flow of logistics and people in modern industrial society. However, since the 1970s, especially in recent years, with the high-speed railway becoming the focus of world attention, railways have regained a decisive position in the transportation pattern of various countries. The speed of trains in France, Japan, Russia, the United States and other countries has developed rapidly from 200 kilometers to 300 kilometers per hour. According to the international railway conference held in 1995, by the end of this century, the operating speed of high-speed railways in Germany, Japan, France and other countries will reach 360 kilometers per hour.
However, in order to keep the train running at such a high speed, the traditional system composed of wheels and rails is powerless. This is because the traditional wheel-rail adhesion railway uses the adhesion between wheels and rails to make the train move forward. Its adhesion coefficient decreases with the increase of train speed, but its running resistance increases with the increase of train speed. When the speed increases to the intersection of the adhesion coefficient curve and the driving resistance curve, it reaches the limit. According to researchers' calculations, the top speed of ordinary wheel-rail trains is about 350-400 kilometers per hour. If noise, vibration, wheel and rail wear and other factors are taken into account, the actual speed cannot reach the maximum speed. Therefore, the high-speed trains running in Europe and Japan have little potential in speed. To further improve the speed, we must turn to a new technology, which is an unconventional train-maglev train.
Although we still call the track of maglev train "railway", these two words are not appropriate enough. Take the railway track as an example. In fact, it no longer exists. There is only one track left, which can't be called "track" because the wheels didn't run over it. In fact, maglev trains don't even have wheels. This super train running on the "railway" has no traction locomotive in the traditional sense. It does not touch the ground when running, but "flies" at a height of 10 cm from the track. Maglev train is a high-speed maglev train system with contactless electromagnetic levitation, guidance and drive system. Its speed can reach more than 500 kilometers per hour, making it the fastest ground passenger transport in the world today. It has the advantages of high speed, strong climbing ability, low energy consumption, low noise during operation, safety and comfort, no oil consumption and little pollution. And the overhead way is adopted, which occupies less cultivated land. Maglev train refers to the use of the basic principle of magnetic force to suspend these trains on the guide rail to replace the old steel wheels and track trains. Magnetic levitation technology uses electromagnetic force to lift the whole train car, get rid of annoying friction and unpleasant clang, and realize rapid "flight" without touching the ground and fuel.
Physical knowledge tells us that two magnets repel each other when they are near the same pole and attract each other when they are near the opposite pole. The seemingly mysterious levitation force that supports the maglev train is actually these two kinds of attraction and repulsion.
According to the accurate definition, the maglev train is actually suspended in the air and guided by electromagnetic attraction or electric repulsion, so that the train has no mechanical contact with the ground track, and then the train is driven by a linear motor. Although the maglev train still belongs to the land rail transit system and retains the characteristics of many traditional locomotives and vehicles, such as tracks, turnouts, vehicle bogies and suspension systems, there is no mechanical contact between the train and the track during traction operation, which fundamentally overcomes the problems of wheel-rail adhesion, mechanical noise and wear of traditional trains, so it may become an ideal land transportation tool that people dream of.
According to the basic principles of gravity and repulsion, there are two development directions of maglev trains in the world. One is the conventional magnetic attraction suspension system-EMS system, represented by Germany. Using the basic principle of conventional electromagnet to attract general iron-containing substances, the train is sucked up and suspended, and the air gap of suspension is relatively small, generally around10 mm. The speed of normally oriented high-speed maglev train can reach 400-500 km/h, which is suitable for long-distance rapid traffic between cities. The other is the exclusive suspension system represented by EDS system in Japan, which uses the principle of superconducting magnetic levitation to generate repulsive force between wheels and rails to make the train suspend. The levitation air gap of this maglev train is relatively large, generally around 100mm, and the speed can reach more than 500 kilometers per hour. It is still inconclusive which of these two technologies is better, but what we hope is that our country's own maglev train can stand up internationally.
Maglev train is the most fundamental breakthrough in railway technology since Stephenson's "rocket" steam locomotive came out about 200 years ago. Maglev train is a new thing today, but its theoretical preparation has a long history. The research of magnetic levitation technology originated in Germany. As early as 1922, German engineer Herman Qiangsuo put forward the principle of electromagnetic levitation, and applied for the patent of maglev train in 1934. After 1970s, with the increasing economic strength of the world's industrialized countries, Germany, Japan, the United States, Canada, France, Britain and other developed countries began to plan to develop magnetic levitation transportation systems to improve their transportation capacity and meet the needs of their economic development. However, the United States and the former Soviet Union abandoned this research project in 1970s and 1980s respectively. At present, only Germany and Japan continue to study the magnetic levitation system, and both have made remarkable progress. The following is a brief introduction to the research situation of maglev railway, a major country in the world.
The Japanese began to study the constant guidance maglev railway on 1962. Since then, due to the rapid development of superconducting technology, the superconducting maglev railway has been studied since the early 1970s. In 1972, the experiment of a 2.2-ton superconducting maglev train was successfully carried out for the first time, with a speed of 50 kilometers. From 1977 to 65438+February, the maximum speed on the Miyazaki Maglev Railway Test Line reached 204 kilometers, and further increased to 5 17 kilometers from 1979 to 65438+February. 1982, 1 1 In June, the manned test of maglev train was successful. 1995, the maximum speed of manned maglev train reached 4 1 1 km during the test. In order to study the feasibility of building a maglev railway between Tokyo and Osaka, the Yamanashi maglev railway test line started at 1990, and the first phase of the test line was completed at 18.4 km.
Germany's study of maglev railway began at 1968 (then Federal Republic of Germany). At the beginning of the research, constant conductance and superconductivity were both important. By 1977, the test cars with the attraction of the permanent magnet and the repulsion of the superconducting electromagnet were developed respectively, and the maximum speed during the test reached 400 km/h. Later, after analysis and comparison, it was considered that the technical level required for superconducting maglev railway was too high and it was impossible to make great progress in a short time, so it was decided to concentrate only on developing a normal-oriented maglev railway in the future. 1978 decided to build a test line with a total length of 3 1.5 km in Amsland, 1980 started construction, and 1982 started the unmanned test. The maximum test speed of the train reached 300 kilometers at the end of 1983, and further increased to 400 kilometers at 1984. At present, German technology in maglev railway research is mature.
Compared with Japan and Germany, the research on maglev railway in Britain started late, starting from 1973. However, Britain was one of the first countries to put maglev railway into commercial operation. In April, 1984, a 600-meter-long maglev railway between Birmingham Airport and Intertenar Station was officially opened to traffic. It takes only 90 seconds for passengers to take the maglev train from Birmingham Airport to Interna Xiongnar Railway Station. Unfortunately, in 1995, this once the only commercial train in the world was declared closed after running for 1 1 years, and its task of transporting passengers was replaced by the airport shuttle bus.
Maglev train is mainly composed of suspension system, propulsion system and guidance system. Although the propulsion system independent of magnetic force can be used, in most of the current designs, the functions of these three parts are completed by magnetic force.
Suspension system: At present, the design of suspension system can be divided into two directions, namely, the normally conductive type adopted by Germany and the superconducting type adopted by Japan. In terms of levitation technology, it is electromagnetic levitation system (EMS) and electromagnetic levitation system (EDS).
Electromagnetic levitation system (EMS) is a kind of gravitational levitation system, which is produced by the mutual attraction between the electromagnet combined on the locomotive and the ferromagnetic track on the guide rail. When the normally guided maglev train works, firstly, the electromagnetic attraction of the lower suspension of the vehicle and the guiding electromagnet is adjusted, and the train is suspended through the magnetic reaction with the windings on both sides of the ground track. Under the action of the guiding electromagnet and the track magnet at the lower part of the vehicle, the wheel and the track keep a certain lateral distance, thus realizing the non-contact support and non-contact guidance of the wheel and the track in the horizontal and vertical directions. The suspension gap between the vehicle and the running track is 10 mm, which is guaranteed by a high-precision electronic adjustment system. In addition, because the suspension and guidance are actually independent of the running speed of the train, the train can still enter the suspension state even when it stops.
The electric suspension system (EDS) uses the magnets on the moving locomotive to generate current on the guide rail. As the gap between the locomotive and the guide rail decreases, the electromagnetic repulsion will increase, thus providing stable support and guidance for the locomotive. However, the locomotive must be equipped with wheel-like devices to effectively support the locomotive during "take-off" and "landing", because EDS cannot guarantee suspension when the locomotive speed is lower than about 25 mph. EDS system has made great progress under the technology of low temperature superconductivity.
The most important feature of superconducting maglev train is that its superconducting elements have complete conductivity and diamagnetism at quite low temperature. Superconducting magnets are composed of superconducting coils made of superconducting materials. It not only has zero current resistance, but also can conduct powerful current that ordinary wires can't match. This feature makes it possible to make electromagnets with small volume and high power.
The vehicle of superconducting maglev train is equipped with on-board superconducting magnets to form an induction power integration device, and the driving winding and floating guide winding of the train are installed on both sides of the ground guide rail. The induction power integration device on the vehicle consists of a power integration winding, an induction power integration superconducting magnet and a floating guide superconducting magnet. When three-phase alternating current with the same speed and frequency is provided to the driving windings on both sides of the track, a moving electromagnetic field will be generated, thus generating electromagnetic waves on the train guide rail. At this time, the vehicle-mounted superconducting magnet on the train will receive a thrust synchronous with the moving magnetic field, and it is this thrust that pushes the train forward. It works like surfing. Surfers stand on the waves and are pushed forward by the waves. Like surfers, superconducting maglev trains have to deal with the problem of how to accurately control the motion at the peak of moving electromagnetic waves. Therefore, a high-precision instrument is installed on the ground guide rail to detect the position of the vehicle, and the supply mode of three-phase alternating current is adjusted according to the information sent by the detector, so as to accurately control the electromagnetic wave shape and make the train run well.
Propulsion system: the maglev train is driven by the principle of synchronous linear motor. The electromagnet coil supported on the lower part of the vehicle is equivalent to the excitation coil of the synchronous linear motor, and the three-phase moving magnetic field driving winding on the inner side of the ground track is equivalent to the armature and the long stator winding of the synchronous linear motor. According to the working principle of the motor, when the armature coil as the stator is energized, the rotor of the motor is driven to rotate due to electromagnetic induction. Similarly, when the substations arranged along the line provide three-phase frequency modulation and amplitude modulation power to the driving windings inside the track, the bearing system and the train are pushed to do linear motion similar to the motor "rotor" due to electromagnetic induction. Therefore, in the suspended state, the train can completely achieve non-contact traction and braking.
Generally speaking, alternating current flowing in the coils located on both sides of the track can turn the coils into electromagnets. Because of its interaction with the superconducting electromagnet on the train, the train starts. The train moves forward because the electromagnet (N-pole) at the front of the train is attracted by the electromagnet (S-pole) installed on the track earlier and repelled by the electromagnet (N-pole) installed on the track later. When the train moves forward, the direction of current in the coil will be reversed. The result is that the original S-pole coil is now an N-pole coil, and vice versa. In this way, due to the conversion of electromagnetic polarity, the train can continue to run forward. According to the vehicle speed, the electric energy converter adjusts the frequency and voltage of alternating current flowing in the coil.
Propulsion systems can be divided into two types. The "long stator" propulsion system uses a linear motor wound on the guide rail as the power part of the high-speed maglev train. Guide rails are expensive because of their high cost. The "short stator" propulsion system uses a linear induction motor (LIM) wound on a passive track. Although the short stator system reduces the cost of the guide rail, LIM is too heavy to reduce the listed payload capacity, resulting in higher operating cost and lower potential income than the long stator system. The adoption of non-magnetic energy system will also lead to the increase of locomotive weight and decrease the operating efficiency.
Guidance system: The guidance system is a direction finding force to ensure that the suspended locomotive can move along the guide rail. The necessary thrust is similar to levitation force, and can also be divided into attraction and repulsion. The same electromagnet on the locomotive floor can supply power to the steering system and suspension system at the same time, or an independent steering system electromagnet can be used.
As the fastest ground transportation at present, maglev train technology does have incomparable advantages over other ground transportation technologies:
First of all, it overcomes the main obstacles of traditional wheel-rail railway speed increase and has broad development prospects. The first wheel-rail railway appeared at 1825. After 140 years' efforts, its running speed only exceeded 200 km/h, and it took nearly 30 years from 200 km/h to 300 km/h. Although the technology is still progressing and developing, there is little room for further speed increase, but it is very difficult. It should also be noted that the speed of wheel-rail railway is very high. The cost of a high-speed railway with a speed of 300 kilometers per hour is nearly twice as high as that of a quasi-high-speed railway with a speed of 200 kilometers per hour and 3 to 8 times higher than that of an ordinary railway with a speed of 120 kilometers per hour. If the speed continues to increase, its cost will rise sharply. In contrast, the world's first miniature maglev train appeared in Germany in 1969, and Japan made it in 1972. However, just ten years later, in 1979, maglev train technology set a speed record of 517 km/h. At present, the technology is mature and can enter the construction stage of 500 km/h actual operation.
Secondly, the speed of maglev train is high, with ordinary maglev reaching 400-500 km/h and superconducting maglev reaching 500-600 km/h. For passenger transport, the main purpose of increasing the speed is to shorten the travel time of passengers, so the requirement for running speed is closely related to the length of travel distance. Various means of transportation play a key role in different travel distances according to their own characteristics such as speed, safety, comfort and economy. Experts' analysis of the total travel time and travel distance of various vehicles shows that when the travel distance is less than 700 km, the 300 km/h high-speed wheel-rail is better than the airplane. The high-speed maglev with 500 km/h will travel more than 1500 km.
Third, the energy consumption of maglev train is low. According to the research and actual test results in Japan, at the same speed of 500 km/h, the energy consumption per kilometer of maglev train is only 1/3 of that of aircraft. According to German experiments, when the speed of TR maglev train reaches 400 kilometers per hour, its energy consumption per kilometer is the same as that of high-speed wheel-rail train with a speed of 300 kilometers per hour. When the speed of maglev train also drops to 300 km/h, its energy consumption per kilometer is 33% lower than that of wheel-rail railway.
Although maglev train technology has many advantages mentioned above, it still has some disadvantages:
1. Because the magnetic levitation system completes the functions of levitation, guidance and driving by electromagnetic force, the safety guarantee measures of magnetic levitation after power failure, especially the braking problem of trains after power failure, are still problems to be solved. Its high-speed stability and reliability need long-term testing.
2. Normally-conducted magnetic levitation technology has a low suspension height, so the requirements for line flatness, subgrade settlement and turnout structure are higher than those of superconducting technology.
3. Superconducting magnetic levitation technology consumes more energy than conventional magnetic levitation technology because of eddy current effect, and its cooling system is bulky. Strong magnetic field has influence on human body and environment.