Electrical Disturbances from High Speed Railway Environment to Existing Services

Abstract

New high speed lines are becoming more and more frequent. These new lines due to their power needs are constructed with a new electric system in order to be able to meet the power demands of the rolling stock and to lessen the electrical losses of the system. There are special cases like the Spanish one where new lines are built in parallel with the existing ones due to lack of space when entering populated zones. This line deployment is more usual in the access to the railway stations in big cities. In this case both lines interfere with each other for several kilometres. The Spanish case is especially interesting because both railway systems work together and there are also points of rolling stock transference between both lines due to the gauge changing facilities and train units that allow trains to operate in both systems. The main cause of electrical disturbances for the already existing services is the electrification system of the new high speed lines. These lines are electrified with 1x25 kV or 2x25 kV 50 Hz systems. These systems, since they use AC, provoke electromagnetic disturbances in the nearby environment. The most prone-to-be-affected systems among the existing lines are the track circuits that use 50 Hz for train detection and the wired signalling and telecommunications systems that run in parallel to the railway line. Track circuits are the most used elements in order to detect train presence in a track section of the line. There are other systems like axle counters that are also used to detect train presence in a section. Most of the deployed track circuits use a 50Hz signal in order to detect the train. Modern track circuits use audiofrequency signals for this purpose and this kind of elements are used in the new built lines, but since is a very reliable safety item there’s no need to replace them unless new disturbances can affect this safety related equipment. The effects of these electrical disturbances can be also affect people. Induced voltages or currents can exceed the limits of the standards or laws. For example EN 50122: Railway applications. Fixed installations. Protective provisions relating to electrical safety and earthing defines the limits for AC and DC transients and continuous voltage in the railway environment.