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The usual voltage for these motors is 3,000 volts, but in the polyphase plant designed for the Cascade Tunnel 6,000 volts are to be used. They possess many advantages, especially their ability to run at overload, and consequently a locomotive with polyphase motor will run up grade without serious loss of speed.
An increasingly intense demand must thus spring up for systems of long distance transmission, and very high voltage will be adopted as the means of diminishing the loss of power due to leakage from the cables. Similarly the "polyphase" system which is eminently adapted to installations of the nature indicated must demand increasing attention.
The simple drawing on the ground led to the design of the first induction motor driven directly by A.C.electricity. Tesla emigrated to the U.S.A. in 1884. During the first year he filed no less than 30 patents mostly in relation to the generation and distribution of A.C. mains electricity. He designed and built his 'A.C. Polyphase System' which generated three-phase alternating current at 25 Hz.
With the polyphase current a motor with a rotating field is used, and they have considerable efficiency as regards weight when compared with the single phase and with the direct current motor.
Basically the ship was an ion-jet job with atomic primaries and a spindizzy converter that might possibly take her up as high as middle yellow Cth far enough to give her a good turn of speed, but not enough to compensate for timelag. Her screens were monstrosities, double polyphase lattices that looked about as spacetight as so many sieves.
The polyphase motor, however, is open to the objection that it does not lend itself to regulations as well as the direct current form, and with ingenious devices involving the arrangement of the magnetic field and the combination of motors, various running speeds can be had.
With alternating current there can be used the various forms of single phase or polyphase current familiar in power work, but the latter is now preferred, and in Europe and in the United States in the latter part of 1908 the number of single phase lines was estimated at 27 and 28 respectively, with a total mileage of 782 and 967 miles. A trolley wire or suspended conductor is used.
This new plant takes high-tension polyphase current from a water-power thirty or forty miles away at Paderno, on the river Adda, flowing from the Apennines; but delivers low-tension direct current for distribution to the regular Edison three-wire system throughout Milan.
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