Home >> Encyclopedia Americana, Volume 26 >> Thacher to The Cualnge Tam B6 >> Third Rail System_P1

Third-Rail System

steam, electric, coal, trains, power, railway and roads

Page: 1 2

THIRD-RAIL SYSTEM, in electric rail way construction, a method of supplying trains on an electric railway with current sent through a conductor located on the track and termed a third rail. Being the first electric system for handling heavy traffic, it possesses unusual in terest. In starting a train of five cars by elec tricity, from 500 to 1,200 amperes are required.

If such currents were passed through a trolley wheel, very excessive arcing would be caused, due to the fact that the wheel touches the wire at only one point. The contact surface is not sufficient to carry this current, and burn ing of the wheel and trolley wire would result. With a sliding shoe, however, instead of a sin gle point of contact, there is a surface about six inches long by two inches wide, and two of these in use at once under normal conditions. The third-rail system differs from the ordinary trolley road only in detail, the principle of oper ation being similar. These details, however, are such as to make possible the application of electric traction to heavier trains than has been found practicable with the overhead trolley, and the system has thus broadened the field for the application of electricity to railway work, so as to bring it into successful competition with steam for the heaviest classes of service. The reasons for its general adoption on ele vated roads were on account of the advantages peculiar to electric traction itself, namely: The reduction in the cost of power is ob tained largely from the generation of power in a single central steam plant, instead of a great number of smaller plants, as with the steam locomotive system. On this point of economy the fuel bill is one of the large items in the operation of a railroad. With steam locomo tives, such as were formerly used on the Chi cago elevated roads, the only fuel available cost in the neighborhood of $3.50 to $5.50 per ton, whereas, in the modern power house, desig.ned for electric railway systems, coal ranging from $1.25 to $1.75 a ton was burned with entire success during the period of low prices for coal. When to this is added the enormous loss in radiation from a large nurnber of steam loco motives, exposed as they are in running over the line of the road, and we compare this with the relatively small loss experienced with a well-constructed stationary boiler plant, it is not surprising that the cost for coal per car mile on the electric railways in Chicago is about one third the cost per car mile with steam loco motives. The comparison is particularly favor

able in Chicago on account of the ability to obtain a very cheap grade of coal directly from the Illinois and Indiana coal fields. In New York and other eastern cities, this difference is not so great, as coal delivered at those points is necessarily higher in price on account of larger freight charges. Besides the saving in the coal bill, there is a further gain by the use of large compound-condensing engine units. These large steam units having a comparatively steady load, develop power with a very much lower steam consumption than the small engines of a locomotive with their constant starting and stopping, and consequent cooling of cylinders, etc. Another item in which a considerable sav ing is made is in the cost of repairs and re newals to the motor equipment as compared with locomotives.

The second advantage—increase in capacity for handling passengers—is due, first, to the fact that with electric motors a much higher rate of acceleration can be obtained in starting trains, thereby increasing the average speed over a given line of road. The trains can also be handled with so much greater accuracy and precision that a much shorter interval is per fectly safe, all of these directly contributing to the end of greater capacity.

The third item— service more attractive to the public generally—is proved by the facts of the absence of smoke and steam, and the great reduction in noise, these being especially impor tant in systems passing through the heart of a large city, as is the case with elevated roads. In regard to the use of the third-rail system on interurban roads, the same general consider ations apply as to the economy of operation, except that, trains being less frequent, the econ omy tn the power generation is not so great an item. There is another field for the third-rail electric railway system, which has been de veloped by the New York, New Haven and Hartford steam road, and that is the use of light trains for suburban and interurban serv ice on many of their branch lines.

Page: 1 2