Earthing short-circuiter
The earthing short- circuiter ( EKS for short ) is a protective device that prevents the occurrence of an impermissibly high contact voltage. It belongs to the group of voltage limiting devices and is used in the area of direct current railways.
scope of application
Earthing short-circuiters are switched between the running rails as the return line of the direct current path and the objects to be protected as building earth. First of all, the traction current is supplied with power rails or overhead lines . The return current is conducted over the rails. Depending on the amperage of the return current, the electrical resistance of the return conductor, the distance to the next substation , the nature of the surrounding soil and the electrical insulation between rail and underground, the potential on the running rail and on all electrically conductive parts connected to it (e.g. B. the railway wagon) compared to the building earth. In order to increase the potential in the area of dangerous contact voltages, e.g. B. to prevent between platform and train, building ground and return conductor are briefly electrically connected by earthing short-circuiters. A permanent connection between the return conductor and the building ground should be avoided, since stray currents to the building ground lead to corrosion of metallic components on buildings and bridges and thus to destruction.
construction
An earthing short-circuiter consists of the short-circuiting element, the measuring sensors and control electronics. In order to enable a short switch-on time and high currents - up to several thousand amperes - the short-circuiting element consists of a combination of thyristors and a contactor , which are controlled simultaneously. The thyristors can establish the electrically conductive connection very quickly in a few milliseconds, whereby the contactor switches more slowly due to the massive mechanical structure. When the contactor has established a conductive connection, the thyristors are switched off again, as they can only carry the high currents for a short time. The contactor is also switched off again after 10 seconds. The measuring sensors monitor the potential differences between two or more relevant points and generate a renewed switch-on pulse for the contactor and the thyristors when a defined threshold value is exceeded. The control electronics are connected to a control room and can be remotely monitored.
Relation to the standards
The standards DIN EN 50122-1 (Railway applications - Fixed installations - Electrical safety, earthing and return; Part 1: Protective measures against electric shock) and DIN EN 50122-2 (Railway applications - Fixed installations - Electrical safety, earthing and return; Part 2: Protective measures against the effects of stray currents from direct current railways provide a set of rules for reducing the existing risk potential.
The standard defines the requirements for protective measures against the effects of dangerous voltages or currents that are caused by the operation of DC railroad power supply systems, including when AC and DC railways influence each other. People can be protected by obstacles, distances or voltage limiting devices. Earthing short-circuiters are one version of these voltage limiting devices. This standard applies to all new routes, major changes and extensions of all railways and local transport systems.
Individual evidence
literature
- Swiss Association of Road and Transport Experts: Earthing Manual. Railway technology regulations, Bern 2008