Electromagnetic compatibility for communications based signaling systems

The results of an investigation which occurred at the Docklands Light Railway, London, UK, in the fall of 1994 are presented. Alcatel´s SELTRAC system was being installed and commissioned on an operating railway. The existing signaling system for the railway had been installed by General Electric Corporation, Alsthom Signaling Limited (GASL) of the United Kingdom. Both systems are transmission based, and used a cable laid down the center of the guideway for communications with vehicles. Problems were noted at various points of the guideway, and an investigation conducted to determine the source of the problems, and to implement corrective actions. The investigation first focused on external interference, then turned to interference between the two signaling systems, the complex interaction of the systems, the ironwork of the guideway, and the ballast resistance of the track. The steps of the investigation are presented, along with the results, the coupling mechanism which was ultimately responsible, and the corrective actions which were successfully implemented