Electric Locomotives

Electric locomotives transform electricity received from the fixed-line electricity network constructed for this purpose into mechanical work necessary for traction. As electricity cannot be stored inside the railway traction capacity, a link to the feeding network is essential for electric locomotives to run. (However, battery powered electric locomotives do exist on local railway lines.) The usual design for the feeding network is the overhead contact line, where the electricity is received by the vehicle via its current collector attached to the overhead contact line located above the track.On some special railway lines the feeding network may also be constructed as a bus bar or a lower contact line. The design of the electric transmission gear of the locomotive is primarily defined by the voltage and frequency of the electric feed network. During the course of history, several pairs of voltage levels and frequencies evolved on European railway lines. The umbrella term for these is “traction systems”. The machinery of the electric locomotive is in fact a converter which transforms a given voltage – of a level and frequency typical of the traction system – into one that is of the necessary level and voltage for feeding the traction engines. Parameters of the driving gear may be changed in such a way that the velocity and the tractive effort of the locomotive is adjustable efficiently throughout the whole velocity range.

With electric locomotives, only a part of the energy conversion, necessary for traction, is performed inside the vehicle. As a result, electric locomotives boast the most advantageous performance-mass ratio amongst all locomotives. Thus, with respect to size and mass limitations of the railway industry, it is of electric locomotives that the highest traction performance may be expected. The greatest disadvantages of electric traction are the fixed line overhead contact line (utility), the traction substations (converters) and the high upfront costs of an electric distribution network.