ELECTRIC LOCOMOTIVES An electric locomotive may be any type of vehicle capable of running on a railway and deriving its power from electric motors appropriately connected in turn to the drive wheels. Electric locomotives exist in an almost endless number of sizes, types and character suitable for service in mines, industrial plants and light railways and for operation on main line railways in all kinds of service. They usually receive their power from some contact system parallel to the track but they also include loco motives which carry their own power plants, such as oil-electric or gas-electric generating sets or batteries with stored power. The wide-spread application of electric power for universal use in industry has prompted much consideration of the substitution of electric for steam operation of railways, but the actual aggre gate in accomplishment has been comparatively limited to date. For such application the general requirement will be a locomotive not less, as to power and service, than the equivalent and, in general greater than that, of the steam locomotive replaced. This article is confined to this sort of locomotive.
The essential requirement for main line electric locomotive operation is the continuous supply of electrical power which must be obtained from a conducting system along or over the railroad way by means of appropriate current collecting or con tact devices carried on the locomotive. The electric power may be at various voltages from a nominal 600 volt direct current up to 22,000 volts alternating current and in prospect even higher. The current used in the contact system determines the designation of systems of electrification; i.e., when the working conductor distributes direct current it is the direct current system; when single phase alternating current is used in the line, it is the single phase system; and when the line current is three phase alternating current, it is the three phase system. The direct current system may be so-called high or low voltage, the former term including those having more than Boo volts on the working conductor. The character and type of the electric traction motors
influence the characteristics of an electric locomotive, as well as their arrangement and drive. In the assembly and grouping of the motors there is a possible variety in mechanical type and assembly almost without end.
Single phase alternating current is standard for railway electri fication in Norway, Sweden, Germany, Austria and Switzerland, and the frequency of the supply is 15 to 16i cycles. Three phase alternating current for railway service predominates in Italy with some 600 m. and about 500 locomotives now in operation with a nominal contact line voltage of 3,30o volts. The general ob jection to the use of more than a single contact line for each track has acted to limit the use of this system elsewhere. Direct current at 1,500 volts has been adopted in France, by Government stipulation as standard for railroad electrification, and during recent years a limited programme of electrification has been embraced by the leading railroads. Single phase alternating cur rent at 25 cycles prevails in the United States with increasing favour, although there is one notable installation of 3,00o volts direct current. There are also terminal and some other instances where direct current is used at 600, i,5oo and 2,400 volts. There have been undertaken throughout the world limited electrifica tions in Great Britain and her colonies, in Japan, Chile, Brazil, Spain, Holland, Java, Czechoslovakia and Mexico. Except for America, where fuel supplies are abundant, the reason for electri fication has been, in general, the desire to secure economy in operation largely due to the saving in fuel obtained by the use of hydro-electric power supplemented in some cases by stationary steam-driven generating plants. In England and in Australia the electrifications have mainly been carried out with multiple unit car service instead of locomotives to secure an improvement in capacity and service in the metropolitan and suburban districts.