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SECTION I
ANALYSIS OF MAGLEV SYSTEM
Working functions and peculiarities.
Any type of Maglev system consists of three following functionally different subsystems: a magnetic suspension; a propulsion motor; and a power system.
Each of the three performs its own working functions:
- the magnetic suspension is supposed to ensure a stable suspension of a vehicle in its own magnetic field;
- the propulsion motor should produce a propulsion force sufficient for a stable flight of the vehicle along an assigned track with a given speed;
- power system should insure uninterrupted power supply with three-phased current.
Ability to perform its working functions immediately without involving intermediate link (such as a servo control system) is most desirable for stable work of each the above subsystems.
Maglev’s distinguishing feature from other types of transportation that its vehicle flies without leaning against substantial medium. It is maintained on the assigned trajectory only by internal magnetic forces. Therefore any impulse of an external force causes natural oscillations of the vehicle with an amplitude equaled to the shift. A secondary suspension is capable to damp rapidly the oscillations with their amplitude not exceeding 2 mm. If the amplitude exceeds 2 mm. they become dangerous for passengers’ life. Therefore the permissible short-lasting deviation of the vehicle from the assigned track must not exceed 2 mm.
A lateral gust of wind may produce short-lasting pressure on a flying vehicle up to 7 t. The ratio of this force to the permissible shift of the vehicle d= 2mm determines the lower limit of the stabilizing force stiffness which equals 3.5×107N/m.
Main problems:
Two unsolved problems delay commercial operation of existing variants of Maglev
- maintaining a strictly limited deviation (2 mm) of a vehicle freely flying with the speed 25-150 m/s from its trajectory assigned by guideway surfaces, and
- ensuring stable work of a linear propulsion motor at vehicle speed continuously varying from 25 to 150 m/s.
A correct solution of the main problem is to make both Magnetic suspension and Propulsion motor self-regulating. Self-regulation for Maglev means its capability of instant and automatic reaction to any deflection of the vehicle speed from its given value and any deviation from its position on an assigned trajectory by producing certain internal magnetic stabilizing forces sufficient to eliminate such variations.
Mechanisms of creating internal forces.
There are three possible mechanisms for producing internal magnetic forces in Maglev:
- the first (the most intensive and the simplest) is to produce attraction forces by magnetization of steel by rare earth permanent magnets;
- the second one (requiring direct current sources) is magnetization of steel by a direct current: and, finally,
- the third one (which is extremely energy consuming and much less intensive) is to produce repulsion forces by moving superconductive magnets over a conductive plate.
It is expedient to compare the values of the forces produced by all of the above ways. The forces of attraction of a rare earth magnet to a steel strip are three times greater than those of electromagnet and almost 100 times greater than repulsion forces of a magnet from a moving aluminum strip.