Page:Popular Science Monthly Volume 74.djvu/220

216 to be regarded that it is now often used for crossings of telegraph, telephone and transmission wires in place of the usual cradle or network of wires stretched between the two lines. The values of voltage now advocated for railway and transmission work have caused considerable criticism and opposition. This is probably due in large measure to the long standing figure of 600 volts for trolley service; this figure, however, is fixed by the character of the direct current motor and not by any consideration of possible danger from shock. A further source of disturbance by electrical operation is the interference by electrostatic and electromagnetic induction between the transmission conductors and the telegraph and telephone lines in the vicinity. Methods have been developed, however, and are at present in use by which such disturbances are prevented at slight cost.

A decrease in the operating expenses has already been stated as one of the means by which electric operation may be made to pay. The operating expenses of an average steam railroad may be roughly divided as follows: Maintenance of way 21 per cent., maintenance of equipment 19 per cent., conducting transportation 56 per cent., general expenses 4 per cent. Considering these items under electric operation the greatest saving is effected in the item of conducting transportation, which includes the cost of coal. The steam locomotive consists of a boiler and engine. For obvious reasons neither is as efficient as the same apparatus of a stationary type. The same amount of coal in a locomotive boiler will evaporate only about two thirds as much water as in a stationary boiler. The average steam consumption of a good locomotive engine is about 30 pounds of steam per horse power hour developed; turbo-generators are now guaranteed for a consumption of only 15 pounds of steam per electrical horse power at the switchboard. As offsetting these marked advantages it is necessary to consider the electrical losses in the transmission system and in the motor equipments. Speaking roughly, 75 per cent, of the electrical energy supplied by the switchboard is available at the wheels of an electric train for tractive effort. These figures indicate that an electric locomotive requires less than one half the amount of coal used by the steam locomotive giving the same horse power output. Further than this, it has been estimated that for every hour that a locomotive is standing idle, with steam up, 400 pounds of coal are burned. The excess of useless mileage and the excess ton mileage owing to the greater weight of the steam locomotive have already been noted, and are also causes for excess coal consumption. As opposed to these, there is the light load coal consumption of the power station. The final value of the balance in coal saving will depend on the proportion of time in which the power station operates to its full capacity. Based on careful comparative tests of steam and electric locomotives the engineers of one of the large