A real alternative in railway transport: The vacuum tube train

Transportation and sustainability – two concepts, which are more and more associated with each other. Due to the requirements for effective and environmentally friendly transport systems, in the near past basically public transport had become favoured. However, it has also become clear that the current global processes cannot be reversed solely by the primary usage of traditional public transport tools, this way only the effects can be deferred at the most. Revolutionary new approaches and technologies are necessary while preserving the existing advantages too. The following idea shows such a superb solution in the case of railway transport. The essence of this idea on the one hand is to preserve and develop the safety attributes of the metro by separating the space of the tunnel and the metro station, and on the other hand to provide a significantly more effective, and at the same time more sustainable transportation. The main aim of development regarding the present metro transportation is increasing its safety attributes. As the metro operates in a closed space, the escaping solutions are limited, and in the case of any kind of accident (e.g. fire, poisonous materials in the air) the possibility to easily localise and isolate the sources of danger is very important. Furthermore the exclusion of the most frequent type of accidents (falling into the tunnel from the platform) and the possibility of committing suicide is also a very important issue to be solved.

At the same time by examining the basic structure of the metro tunnels, it is clear that the space of the tunnels only opens up to the platforms at the stations. The essence of the new solution is that the structure of the metro tunnels would be similar to the structure of the elevator shafts, meaning that a double door system would be designed; one layer of this system consists of the conventional doors of the metro carriage itself, while the other layer consists of the doors located on the separating wall between the platform and the tunnel. The usage of such a separating wall has several advantages; the only difficulty to be overcome is the accurate stopping of the metro trains exactly on the location where the two door systems overlap each other. This problem can be solved very easily, the same way elevators have been operated for a long time. However, the advantages of such a solution are multivarious: the first and most important is the safety of the passengers, since by using such a separating wall both of the cases of accidentally falling into the tunnel and committing suicide become impossible. Furthermore the trains can become completely automated, as there would be no need for the highly complex and expensive detecting system, which is currently required to be integrated into the automated trains. The new solution featuring the separation of spaces increases the safety of both the metro stations and the entire metro line. E.g. in case a fire occurs in the tunnel or dangerous materials get into the air, then the metro station can be easily isolated from the tunnel and the trains, and vice versa, if there is a similar accident at the metro station, the trains in the tunnel can be securely isolated from the danger.

The possibility and the advantages of pumping the air out of the tunnels As a result of the separation of the metro stations from the tunnels this way,

the entire tunnel system can be closed and isolated, provided that the end stations are beneath the surface. Only the isolation must be hermetic, especially regarding the double door- (airlock-) system, in order to pump the air out of the tunnel system.

Pumping the air out of the tunnel results the following advantages: i. The decreasing of the energy consumption of the train

As there is no more air-drag in the tube, neither is there any more energy loss resulting from the eliminated air-drag. At the same time it is widely known that present day railway transportation requires much less specific energy than road freight, thanks to the extremely low rolling resistance.

This rolling resistance can be further reduced by increasing the diameter of the wheels and choosing appropriate materials (ceramics, high tensile steel alloys). Furthermore by increasing the diameter of the wheel the same maximal speed can be reached with a much lower motor rev, which significantly increases the lifespan of the trains.

In the case of the metro trains the role of the air-drag is even more determining, since while a train on the surface does not change the density of the air significantly, in a tunnel the air must stream between the wall of the tunnel and the train, which can significantly increase the rate of the air-drag. This is the reason why nowadays the diameter of the tunnel must be remarkably greater than the diameter of the trains. The usage of vacuum in the tunnels enables the reducing of the diameter of the tunnels, which is very important, as the greatest financial part of establishing new metro lines is the digging of the tunnels. ii. The possibility of gaining back energy

As it can be seen, both the air-drag and the rolling resistance can be significantly reduced (to a neglectable level), thus only the accelerating of the train requires a significant amount of energy. However, the train must be decelerated at the end of the travelling section. In this case it is worth using such a solution, which is very well known and widely used in electric and hybrid cars; the essence of this solution is that the electric engines act as electric generators during the process of decelerating by turning the kinetic energy into electric energy, opposite to the traditional brakes, which turn the kinetic energy into thermal energy (and this way losing the possibility of reusing the energy).1 iii. The possibility of high speed travelling In the case of the currently used high speed railways (e.g. the TGV) it is the air-drag, which limits the maximal speed. If there was not any air-drag, extremely high speed values could be reached, e.g. even the speed of sound could be exceeded as there is no sonic boom in the vacuum tunnel. The usage of the already mentioned high diameter wheels enables a speed significantly higher than the speed of airliners, even by the rev of the currently widely used electric engines. Supposing that the wheel diameter is 3 m and the rev is 3000 1/min (50 Hz, the rev of most of the electric engines), a maximum speed of even approx. 500 m/s can be reached

1 Flemming, Frank; Shapiro, Jessica (July 7, 2009). "Basics of Electromagnetic Clutches and Brakes"

(PDF). Machine Design: pp. 57–58. http://www.ogura-clutch.com/pdfs/The%20Basics%20of%20Electromagnetic%20Clutches%20and%20Brakes.pdf.

(1800 km/h – 150% of the sound speed and 2.5 times faster than ordinary airliners) if the rev of the electric engine is transmitted directly to the wheel.

When comparing both the extreme high speed and extremely low energy consumption with any other transporting or freight vehicle, it becomes clear that the usage of this solution is highly recommended not only by the metro, but also in the case of transportation on the surface, especially on medium- and long range transport routes (transcontinental and intercontinental travelling and freight). The technical details of realization The realization in practice brings forth several difficulties, which are very unusual in the case of building ordinary railways and trains, as these are basically related to the presence of vacuum and the very high speed.

The difficulty related to vacuum is basically the matter of hermetic isolation. In practice all doors must be airlocks, which in fact can be easily realized, as such requirements have been met for many decades both in marine (submarines, oil-rigs etc.) and in aeronautics (over-pressurized cabins, space research).2 Another significant issue is the question of the bearings. Bearings functioning with liquid or viscose lubricants, the so-called plain bearings3 cannot be used, since they function only under ordinary atmospheric air pressure, as the necessary viscosity and other attributes of the lubricants are provided only under the appropriate circumstances. That is why only ball bearings and magnetic bearings can be used. Both can be used besides a relatively low rev (which can be provided by increasing the diameter of the wheels), but in the case of a higher rev only magnetic bearings can be used.

The question of electric energy supply is problematic only because of the high speed. It is clear that in the case of such a high speed (several thousands km/h) traditional current collectors cannot be used at all. However, the solution is provided by the structure itself. In order to enable the electric energy supply contact surfaces between the tunnel and the train are required. It is logical that the wheels themselves are in contact with immobile surfaces of the tunnel. Thus it is practical to use the wheels themselves as current collectors.

The most problematic questions are the power-transmission and the energy supply of the engines, which in this case require a new approach to the well known power-transmission methods and electromagnetic laws. In the followings the construction of the propulsion will be shortly introduced. The first and most important issue is the engine itself. Since in our case the possibility of gaining back the energy used up by the acceleration during deceleration is a basic requirement, only synchronous engines can be used from among the two main types of electric engines (synchronous and asynchronous engines4). The reason for this is that this electric engine type can be used as electric generator without any modification.5 The great

2 http://www.pipelineengineering.com/

3 Weichsel, Dick (1994-10-03), "Plane bearings", ESC Report 5 (1): 1–2, archived from the original on

2009-12-10, http://www.webcitation.org/5lv9I6BuJ. 4 George Shultz, George Patrick Shultz (1997). Transformers and Motors. Newnes. pp. page 159 of

336. ISBN 0750699485, 9780750699488. 5 James Stallcup (2005). Stallcup's Generator, Transformer, Motor And Compressor Book, 2005.

Jones & Bartlett Publishers. p. 2-1. ISBN 9780877656692. http://books.google.com/books?id=OkwGeMAXJa8C&pg=PT22&dq=generator+terms+armature+rotor

disadvantage of synchronous engines compared to asynchronous engines is that they can only function by a strictly limited rev; any divergence from this rev causes the engine to stop. At the same time the asynchronous engine is able to start the rotor from its stationary position and increase its rev until it reaches its maximal value.6 Unfortunately asynchronous engines cannot be used as electric generators. The usage of synchronous electric engines requires a continuously variable transmission system and the providing of a minimal initial speed, furthermore the designing of the rotor and the stator which enables the wheels to function also as current collectors has to be solved as well. The solution is the following: the synchronous electric engines are located directly on the axis of the wheels and as against the traditional, widely used method, the a.c. reels are contained not in the stator, but in the rotor, as the a.c. comes through the shaft (Fig. 1.).

Fig. 1. Schematic structure of a one phase synchronous electric engine, in which the stator contains the permanent magnets (the colours red and blue represent the magnetic north and south pole), while the rotor contains the a.c. reel, which receives the a.c. through the axis.

This is different from the currently used method, in which the train receives the a.c. through traditional current collectors, thus in that case it is practical to incorporate the a.c. reels into the stator. In the case of the new solution the necessary permanent magnet is located in the stator, which can be constructed from ordinary, strong ferromagnetic materials. It is practical to create the permanent magnet from such materials, but it is also possible to use an induction d.c. magnet, if the necessary d.c. +stator+field+mechanical+electrical&num=20&ei=2jTlStQBiMyVBKSpgJEM#v=onepage&q=generator%20terms%20armature%20rotor%20stator%20field%20mechanical%20electrical&f=false. 6 Bernhard Arthur Behrend (1901). The induction motor: A short treatise on its theory and design, with

numerous experimental data and diagrams. Electrical world and engineer. http://books.google.com/books?id=ffpOAAAAMAAJ&printsec=frontcover&dq=induction+motor&source=bl&ots=AWJzYuRVCl&sig=Bm0VKBdRKgCfTPpeR5_YU3BCrso&hl=en&ei=1VS3TNTyNoKKlwfWwJ3MDA&sa=X&oi=book_result&ct=result&resnum=7&ved=0CEUQ6AEwBjgK#v=onepage&q&f=false.

source is provided on the train. This solution, i.e. inverting the position of the a.c. reels and the permanent magnets can be realized also by using three phase a.c. (Fig. 2).

Fig. 2. Schematic structure of a three phase synchronous electric engine, in which the permanent magnets are located in the stator (the colours red and blue represent the magnetic north and south pole), while the rotor contains the

split a.c. reels (which are included in a 120 angular position) and which receive the a.c. through the axis (three phases through three different cables). The mechanic transmission is very important, because the vehicle must be accelerated and decelerated, while the synchronous electric engine/generator functions strictly on a certain rev according to the frequency of the electric network (if the frequency of the a.c. in the electric network is 50 Hz, then the rev of the electric engine/generator must be exactly the same, 3000 1/min). The strictly limited rev and the very wide speed range necessitates the usage of a continuously variable transmission system, which functions very efficiently and safely on this huge speed range; furthermore, it may not detain the usage of the wheels as current collectors, and it must enable the engines to still be positioned on the axis of the wheels. Considering all these requirements the transmission system is the following: the continuous transmission is solved by the geometry of the wheels. In essence the shape of the wheels is conical, and the cross section of the rails is specially designed; furthermore the interaxis of the wheels is variable. Thus if the speed is low, the interaxis is smaller; consequently a smaller circle on the conical surface touches the rails. This way the lower speed can be provided by the same rev. In the case of high speed the interaxis is bigger, a greater circle on the conical shape touches the rail, and thus the higher speed can be provided by the same rev. Furthermore this way the maximum value of speed by a given, constant a.c. frequency depends only on the diameter of the wheel, and by using these conical shaped wheels the speed can be easily changed by changing the size of the interaxis (Fig. 3.).

Fig. 3. The conical shaped wheels rolling with the same rev by medium and by high speed: If the wheel is in a lower position, it touches the rail on a smaller circle (coloured by red), thus the speed is lower. If the wheel is in a higher position, it touches the rail on a bigger circle, thus the speed is higher.

The energy necessary for changing the size of the interaxis can also be gained back, because while the increasing of the distance requires energy, the decreasing (due to the conical shaped wheels) can take place all by itself, so its energy can be gained back during the deceleration. The usage of such wheels also means that the axes change position vertically as well during the trip, since by very low speed they are positioned almost on the same the level as of the rails, while by maximum speed they are positioned almost as much higher as the radius of the wheels (which in this case is quite significant, it can be even 1.5 m). This can be solved easily with appropriate suspension, which is energetically irrelevant, as the position of the axes return to the initial stage at the end of the trip.

To ensure the highest possible speed the diameter of the wheels must be as big as possible; this requires the special geometry of both the vehicle and the tunnel. If using three phase a.c. it is practical to use three pairs of rails instead of one, furthermore the diameter of the wheels should be as big as it is enabled by the structure. The usage of three pairs of rails requires the usage of specifically three times more wheels, since this way three pairs of wheels run on one axis instead of only one pair (and there is a three phase synchronous electric engine located in the centre of the axis); this, however, is specifically advantageous when considering the abrasion and loading of the wheels and the rails (Fig. 4).

Fig. 4. The schematic structure of the rail system (containing three pairs of specially designed rails) and the wheels. The different heights and distances of the axes belonging to different speeds, furthermore the suspension system can be seen clearly.

As the train runs in vacuum, there is no need for a streamlined nose form on the nose of the vehicle. Furthermore, huge stabilizing wheels with vertical axes become necessary, which roll in chases on the walls of the tunnel. These are extremely important in order to ensure stability by very high speed, since without them the train would become instable even in the smoothest curve (Fig. 5.).

Fig. 5. The schematic structure of such a train and a segment of the tunnel. The wheels, which are as big as possible, can be seen clearly. The cabin/cargo bay is located between the wheels, furthermore stabilizing wheels with vertical axes and an extremely great diameter are located on top of the vehicle (thus they have a relatively small rev). These roll in chases on the walls of the tunnel and they provide the necessary stability.

The solving of the last difficulty is very simple. The vehicle must be started from a motionless stage; however, this is impossible with a synchronous electric engine even if a continuously variable transmission system is used. Still the solution is simple: in the initial motionless stage the train stands on a very smooth (>1%) slope instead of on a perfectly horizontal platform. Thus when setting off only the traditional brake has to be released, and the train automatically gains a minimal initial speed, which is already enough to start using the synchronous electric engine. At the end there is a similar slope onto which the train arrives after the synchronous electric

engines functioning as generators have decelerated the vehicle to this minimal initial/final speed. The cost estimation of the realization and the operation of this kind of regional and transcontinental (intercontinental) high speed vacuum tube train The costs of such vacuum tube railways are specifically higher than the costs of the currently widely used types. First of all, their trail and design is similar to the existing high speed railways (TGV). Furthermore the size of the tunnel must be big enough to be able to contain the vehicles, i.e. the diameter of this tunnel must be approx. 5-10 m. Moreover the wall of the tunnel must be able to endure the pressure difference between the vacuum and the outer atmospheric pressure. A very sensitive pressure sensor system has to be built as well, which is able to immediately detect with high accuracy the location of any potential leakage.

It is important to note that such establishments already exist, e.g. oil and natural gas pipes, which transport oil and gas on a very long distance (up to ten thousand km) under very high pressure (which can even be a hundred times higher than the ordinary atmospheric pressure). Thus it can be stated that the construction of such a vacuum tube train costs approximately as much as the building of a transporting pipe with the same length. In our case the wall of the tube is thinner (as the pressure difference is only 1 bar), but the diameter is bigger, and the rails also must be installed. The sensor system is very similar in both structures. In the case of the oil pipes pressure increaser stations have to be installed frequently, while in the case of the railway it is necessary to install transformer stations (which provide the necessary amount of electricity and voltage and to feed the regained energy of the deceleration back into the electric network). On the other hand the cost of maintenance itself is extremely low, in practice only the sensor system and the transformer stations require some energy. The travelling itself requires very little energy, as the kinetic energy is fed back as electric energy into the electric network during deceleration, consequently only the deck and the controlling systems require some energy. The processes can be almost completely automated, thus human labour is only necessary by potential trouble-shooting. Comparing the vacuum tube train to other transport solutions

When comparing the transport alternative offered by the vacuum tube train to

the car traffic and road freight, it becomes clear that the vacuum tube train is faster and its energy consumption is many orders of magnitude smaller than any of the others. The vacuum tube train causes no environmental pollution. Its energy consumption is a very low constant, which is neither proportional with the number of passengers, nor with the mass off the freight; consequently it is many orders of magnitude cheaper. However, in the case of passenger transportation there is no possibility for individual travelling, only for a certain type of public transportation, similarly to the traditional airliners and passenger trains.

When comparing the vacuum tube train to the traditional rail cargo and passenger railway transportation, the vacuum tube train is many orders of magnitude faster, has many orders of magnitude smaller energy and cost demands, furthermore it does not pollute the environment at all.

When comparing it with air transport and air freight, the vacuum tube train is significantly faster(!) (many orders of magnitude faster if the construction is appropriate), many orders of magnitude cheaper, and its energy consumption is even more orders of magnitude smaller, furthermore it causes absolutely no environmental pollution. The same can be said when comparing it with shipping, and it is important to highlight that its specific energy consumption is many orders of magnitude better than any kind of shipping. Summary On the whole it can be declared, that following significant initial investments such a regional and global transport system can be achieved by this technological innovation, which is less expensive, faster, has a low energy demand by many orders of magnitude than any other, currently used transportation tool. Furthermore, as it uses electric energy, it is carbon neutral, thus it is a real, sustainable alternative in transportation, which enables the possibility of maintaining and even improving the existing requirements in transportation (e.g. high speed). References [1] Flemming, Frank; Shapiro, Jessica (July 7, 2009). "Basics of Electromagnetic Clutches and Brakes" (PDF). Machine Design: pp. 57–58. http://www.ogura-clutch.com/pdfs/The%20Basics%20of%20Electromagnetic%20Clutches%20and%20Brakes.pdf. [2] http://www.pipelineengineering.com/ [3] Weichsel, Dick (1994-10-03), "Plane bearings", ESC Report 5 (1): 1–2, archived from the original on 2009-12-10, http://www.webcitation.org/5lv9I6BuJ. [4] George Shultz, George Patrick Shultz (1997). Transformers and Motors. Newnes. ISBN 0750699485, 9780750699488. [5] James Stallcup (2005). Stallcup's Generator, Transformer, Motor And Compressor Book, 2005. Jones & Bartlett Publishers. p. 2-1. ISBN 9780877656692. [6] Bernhard Arthur Behrend (1901). The induction motor: A short treatise on its theory and design, with numerous experimental data and diagrams. Electrical world and engineer.