| masraum |
02-09-2020 01:29 PM |
Quote:
Originally Posted by RWebb
(Post 10747153)
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According to the article, the Japanese beat the French by 6kph (581kph vs 474.8kph) about a week before the French did it, but using maglev (the French did it with wheels or rails). In 2015 the Japanese hit 603kph with a maglev train.
The French were pretty sure that they could have hit 600 in their train, but that's getting awfully close to the speed at which the train would outrun the wave on the wire that fed it power (610kph) which would be bad.
That's something that I hadn't thought about which was interesting in the article, the need to keep the overhead power wire under high tension to keep it tight (no sag).
Quote:
The key factor for very high speed circulation, however, is the mechanical response of the catenary. Its behavior is easy to understand picturing a finger pressing a guitar string. The finger represents the pantograph of a train. By moving longitudinally through the catenary applying a vertical force to ensure the continuity of the electrical contact, the pantograph creates a wave that moves in both directions along each span of automatic compensation of the mechanical tension of the catenary.
The frequency of the generated wave increases with mechanical stress — and for that reason the tighter strings of a guitar sound sharper. But if the finger is pushed along the string instead of just plucking it, the wave ceases to be static and moves at a speed proportional to the mechanical tension and inversely proportional to the mass per unit length of the string material [3].
This idealized scenario is altered by the existence of fixed masses in the overhead contact line, which are indispensable for its mechanical support. Droppers and registration arms, which allow the shape of the contact wire to be maintained by anchoring it to the messenger wire and to the masts respectively, induce reflected waves that alter the behaviour of the entire assembly. At high speeds, the dynamic interaction between the pantograph and the overhead contact line is further complicated by the Doppler effect, which shortens the waves in the direction of travel — while lengthening them in the opposite direction.
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And then there's the fine line of wire size, power transmission and tension.
https://www.researchgate.net/profile...stemblocks.png
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