Double electrification

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Birkenwerder station (b Berlin): The track is electrified with the direct current busbar of the Berlin S-Bahn and the alternating current overhead line of the long-distance railway, 2015

Under a double electrification refers to the equipment of a railway line with the upper line and the busbar , in order, for example, the simultaneous use for long-distance trains and urban railways to allow or even a switch of busbar Overhead line operation (and vice versa) to enable. The latter was the case, for example, with the Hamburg S-Bahn between 1940 and 1955.

Double electrification is only used in exceptional cases, as it can lead to very large problems with the mutual influence of the circuits . As a result of the voltage drop along the running rail, current can flow from the conductor rail system into the overhead contact line system (and vice versa). If one of these systems is a direct current and the other an alternating current system , undesired direct current bias of the transformers in the substations of the alternating current system can occur.

Overhead lines or busbars, which can be fed with different power systems as required, are not referred to as double electrification . Such systems can be found in border stations and railway test routes.