Gyuláné Vincze, Gergely György Balázs
Budapest University of Technology and Economics Department of Electric Power Engineering
Table of Contents
Speed limit of traditional trains rolling on wheels is about 350km/h. At this speed, motive force transferred on the circumference of the wheel and gripping coefficient decrease so as it cannot overcome the increased rolling resistance of the locomotive. Traditional trolley contact become uncertain at high speeds so contact wire current feeding cannot be used. So, when designing high speed vehicles, traditional solutions for energy supply and traction mode must be changed.
Technical problems to be solved in levitated vehicles are:
to create contactless motive force; to design driving systems without mechanical drive and wheels to provide traction and electric brake force
to create levitation force perpendicular to the rail to hold the weight of the vehicle, and to control constant levitation height, if possible
to control lateral movement of the levitated vehicle, to hold the vehicle on the rail during curving, at cross wind etc.
to stabilize vehicle movement, to damp and limit inertial forces that create bias, oscillation, pitching of the vehicle body
to supply electric energy without contact.
There are two main solutions for levitation: air-cushion and magnetic.
Air-cushion vehicles have a long history. First efforts were in 1960s in France, where the so-called “Aerotrain” air-cushion train was developed with gas turbine drive and it reached 300 km/h. Experiments to develop air-cushion systems went in two directions: upper pressure and lower pressure systems.
In case of upper pressure systems high-pressure air layer to hold and support the vehicle is provided by streamed air directed to the path drawn in from above. Levitation force is provided by pressure force and overpressure of air. Two designs of several solutions can be seen in Figure 7.1.a.
At lower pressure systems force needed for levitation is provided by vacuum; air is drawn from space above the vehicle so it is lifted by suction effect (Figure 7.1.b). It can be seen that this solution also solves the problem of side guiding. At upper pressure systems, side guiding has to be solved separately.
Gas turbines, turbo jets or linear turbines are used to drive air-cushion vehicles. Disadvantages of air-cushion vehicles are high required power and high noise, low total efficiency and several technical problems, for example moving in tunnels, steering and creating trains. So, designers turned their attention to magnetic levitation.