Stray current control-an overview of options [DC traction systems]

DC stray current problems in railways has been with us for a long time. There does not appear to be a universal solution to the problem. There are a number of reasons for this such as a lack of standardisation internationally on railway system design; different ownership of possibly affected third parties such as utilities; a different approach to electrical safety between different countries and a different approach to liabilities and responsibilities with regard to prevention at source versus limitation of consequences. There appear to be three fundamentally different approaches to the problem, i.e. (a) the power system is fully insulated and return paths (rails) are solidly bonded to earth at the substations for safety reasons; stray current collection methods are applied to intercept earth leakage currents; (b) the power system is fully insulated and not deliberately bonded at the substation; safety is provided by secondary protection schemes performing a vital function; no special stray current collection methods are provided; and (c) the system is not deliberately insulated from the surrounding environment nor are there any connections made to earth at substations; there is no system of stray current collection. The first two categories apply to LRT systems which are or have been implemented in the UK whereas Continental and United States practice is predominately covered by the latter category. This paper summarises the advantages and disadvantages of each system and their practicability or particular features