In the early electrified railway systems, the design of signal and control networks were not always made in accordance with the strict rules of Electromagnetic Compatibility (EMC). This created problems due to Electromagnetic Interference (EMI) when old electro-mechanical signalling, control and communication systems were replaced by modern sensitive electronic circuits. Modern developments in the railway systems have made the system more vulnerable to lightning transients, a natural source of EMI, because the overall network is not designed to reduce the lightning surges to the low levels tolerable to the electronic systems widely being introduced in the railway system. Railway networks are extensive and modernization of signal/control/communication systems are carried out in stages at different times, it is not unusual to find transient related problems in a section of the network on account of inadequate lightning protection design or EMC design of the existing network in which a new module (equipment or system) is introduced. These problems may act as a brake on the upgrading plans of the railways. Also the new railway systems which incorporate advanced signal/control/communication systems sometimes suffers from the effects of lightning transients because many of the standards and guidelines used in the design dates back to the age of electromechanical devices and hence do not include robust transient protection design. There have been many attempts to address EMC issues in railways, but usually these attempts were confined to solving immediate problems of EMI due to introduction of new locomotive drives and EMI due to sparks at the pantograph. A comprehensive review of railway system from the angle of lightning protection and EMC is not yet fully carried out.
The Swedish National Rail Administration (Banverket) reported a delay of about 900-1000 hours in the years 2001-02. Lightning transients were found to damage important devices that control train movements, causing traffic stoppage and delays. This work therefore discusses the EMC problems of large distributed systems, with particular reference to lightning interaction with Swedish rail networks . Lightning induces transient overvoltages in railway conductor systems such as tracks, overhead wires, and underground cables, either due to direct lightning strike to the system or due to the coupling of electromagnetic fields from remote strikes. Models based on multiconductor transmission line theory were developed for calculating the induced voltages and currents [1-3]. Some experiments have also been carried out to better understand the way in which the lighting transients’ couple into the systems and also to verify the models used for analysis . From experiments high frequency behavior of different types of transformers used within the railway systems were also derived [1, 6]. Besides, experimental studies on lightning induced transients entering railway systems, failure modes of relay and rectifier units used in the train position/signaling applications for lightning transients are performed. The simulation models are being converted to user friendly software for the practicing engineers of the railway industry .