The electric current : how produced and how used / by R. Mullineux Walmsley.

  • Walmsley, R. Mullineux (Robert Mullineux)
Date:
1894
Catalogue details

Licence: Public Domain Mark

Credit: The electric current : how produced and how used / by R. Mullineux Walmsley. Source: Wellcome Collection.

    670/800 (page 654)
    such increase cannot be extended indefinitely, for it soon reaches the limits allowable in practice. Since these considerations of cost fix a limit to the reduction of R, we must turn to the other factor, A (the current), and examine the advantages and disadvantages of reducing it. It is at once apparent that any diminution of A is much more effective in reducing the waste of energy than a corresponding diminution of R, because the waste varies as the square of A, and is only directly proportional to R. Thus, a diminution of the current to -|rd of its previous amount will reduce the waste energy to ^th, if other conditions remain unchanged. To make this still clearer, we may take the example already given of the various currents that might be used to transmit a power of 120 kilowatts to a distance. We arrange the figures in a table Table IX.—Transmission of 120 Kilowatts with Various Currents. Amperage (1Current in Amperes). Relative Values of Waste Heat (Resistance constant). Voltage (Pressure in Volts). 10,000 100,000,000 12 1,200 1,440,000 IOO ICO 10,000 1,200 IO IOO 12,000 I I 120,000 A glance at the second column of this table will show how enormously the waste heat diminishes as the current is reduced, the waste heat in the first case cited being 100 million times that in the last. In actual practice the difference would not be quite so enormous, though it would still be very great, for no one would use the same conductors for a current of 10,000 amperes as for a current of one ampere. Smaller conductors would certainly be