. Machinery for metalliferous mines : a practical treatise for mining engineers, metallurgists and managers of mines. THE PIERREFITTE ELECTRIC POWER STATION. 495 Mine Motor.—The 30-horse-povver motor driving the roller crushersand the loo-horse-power motor driving the Schram air compressor, areshown in fig. 321. It will be noticed that there are four pole differ in size, being of different power, but their appearance is thesame. Their dimensions are given in the preceding list. A strangeaccident happened to this latter motor during my last visit to themine in December, 1900. The mo
. Machinery for metalliferous mines : a practical treatise for mining engineers, metallurgists and managers of mines. THE PIERREFITTE ELECTRIC POWER STATION. 495 Mine Motor.—The 30-horse-povver motor driving the roller crushersand the loo-horse-power motor driving the Schram air compressor, areshown in fig. 321. It will be noticed that there are four pole differ in size, being of different power, but their appearance is thesame. Their dimensions are given in the preceding list. A strangeaccident happened to this latter motor during my last visit to themine in December, 1900. The motor man reported that when restartingafter dinner a flash of fire occurred all around the collector, whereuponhe shut off the current. There was nothing visibly wrong with themachine, but the same event happened when I caused it to be it was more closely examined, and finally the mashed remainsof a rat were found inside the armature, where he had apparently taken. Fig. 322.—Starting Rheostat and Motor. refuge during the dinner hour. His blood caused a short circuitingacross some of the collecting wires, and the machine stood idle a weekfor repairs. The total cost of the works complete was ;^8ooo, and the work wascarried out by contract to my satisfaction. The total efficiency of thesystem worked out at 56 per cent, of the theoretical power in the waterfeeding the turbine. When the distance between the power station and the motors is com-paratively short, the direct current can be used with advantage, but whenit is considerable, then the advantage lies with the use of high tensionalternating currents ; the cable lines for which can be \ of small weightas compared with the low voltage direct current lines. 496 MACHINERY FOR METALLIFEROUS MINES. The Frongoch Electric Power Station.—I am indebted to myfriend Mr. B. Nogara, an Italian engineer, for the following descriptionof an alternating current high voltage plant, which he recently
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