The importance of electrically insulated tracks
A high electrical insulation of the track infrastructure is an important aspect, especially for urban transport modes, such as for light rail and metros. If the railway system is not adequately insulated from the ground, this can lead to damaged tracks and pipes laid underground. Stray currents can cause considerable corrosive damages to the rails, fastening systems and installed track reinforcement. In addition malfunctions in train control and signalling systems are possible effects. Stray currents also lead to the risk of damaging surrounding rusted metallic components that are not part of the railway, such as gas pipes.
The standard EN 50122-2 specifies requirements for protective measures against the effects of stray currents caused by the operation of an electrically powered railway. The following aspects have a significant influence on electrical insulation and should be considered during the track design phase: distance of the substations, return line connections, insulation of the rails from earth and additional measures to improve them.
Often control and signalling technologies, such as train detectors, are in use on the infrastructure to detect and position vehicles, in order to secure the track. The use of such circuits results in specific insulation requirements for the track system. In order to ensure reliable train operation, construction measures must provide defined electrical and magnetic characteristics for track sections in which track circuits are to be installed.
In some cases, the planned slab track is designed with a reinforced in-situ concrete layer. The diameter of the reinforcement also has an influence on the control and signalling systems. Steel reinforcement in the track and track system, such as tie bars or lattice truss girders, dampens the electrical field. If an electrical conductor comes into the oscillating electrical field generated by induction, the frequency will change. For this reason, it is important to ensure a proper electrical insulation of the track system.
In general, a track system is ideally suited if it guarantees a high level of insulation, including a sufficiently large safety buffer to compensate for the difference between laboratory tests and the real condition on the track site.
EBS as safety buffer
The Corkelast® EBS-RF and EBS-UF track systems (EBS) are designed to match these high requirements. The key component of both systems is a prefabricated tray which consists of Geotextile and the Corkelast® elastomer. This material combination ensures a very high electrical insulation. The tray is working as an insulating intermediate layer and will disconnect fastening systems from the track as well as both running rails.
A tie rod is not required for both systems, which results in optimized insulation properties in comparison to track systems where tie bars, tie rods or lattice truss girders are included, for which an additional insulation is required.
In addition to project experiences under real conditions, EBS was tested according to EN 50122-2 and in accordance with DIN EN IEC 62631-3-1 with a test voltage applied from -200 V DC to +200 V DC in steps of 50 V. In a dry state the average conductance per length between the track and the earth was between 11.9 nS/km and 3.7 mS/km, which corresponds to a rail-to-earth resistivity of 270 kΩ km and 462 MΩ km respectively. These values surpass those required according to the norm, which ensures a sufficient safety buffer of the electrical insulation and a trouble free train and circuit operation in practice.
All in all: EBS, your best choice for a high quality electrical insulated track system to protect from risks of stray currents.
For more information please contact our EBS competence center EBS@edilonsedra.com.