51312-01727-Modelling and monitoring stray currents for existing Metro as a result of using voltage limiting dev

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Product Number: 51312-01727-SG

ISBN: 01727 2012 CP

Author: Birit Buhr Jensen

Publication Date: 2012

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A system of VLD's (Voltage Limiting Devices) is installed in the Copenhagen Metro traction system. The purpose of having these VLD’s is for safety reasons. At every Metro station a "57-VLD” is installed.The VLD's will be switched on automatically if the numerical value of the potential at the running rail exceeds the potential at the earthing system by more than 90 volt. Such an incident happens but is according to Metroselskabet not very common and the duration of such short-circuiting incidents is short.In addition to automatic activation of VLDs every night five days a week maintenance works are carried out at specific parts of the Metro track system. These maintenance works are scheduled where specific parts of the track system are taken out of service for about 5 hours. During these periods the VLD's in each end of the mentioned sections are switched on for the safety of the workers.Even when one VLD is switched on (possible scenario for the automatic activation) the track system is changed from being electrically “floating” to a system where stray currents may enter or leave the track system through the VLD. As a safety precaution voltage limiting devices (VLDs) are used The paper presents 1) a mathematical simulation of the electrical currents where a number of the “57-Voltage limiting devices (VLD’s)” are activated.2) Monitoring results of the track system during periods where a number of the “57-VLD’s” are activated.The monitoring results are in line with mathematical simulation of the electrical currents and that VLDs comprise a considerate corrosion risk that should be considered.