Application of HV insulation coordination techniques to DC railway systems

Some sections of urban railway systems may run on the surface and therefore may be exposed to lightning strikes. Reliability of service, particularly in areas with high keraunic levels may be severely affected by lightning damage to power system equipment. Specific problems are related to sections over bridges and viaducts where effective earthing is often difficult. This paper describes practical means of protecting a typical DC overhead traction power supply system from lightning strikes. A section of track from a major urban mass transit system was selected for investigation. This particular section has in the past sustained lightning damage to parts of the power supply system. A computer model of this system was developed using the Electromagnetic Transients Program (EMTP). This program, which is more generally used for HV applications, was adapted for the overhead catenary configuration of a DC traction supply. The program was used to simulate a lightning strike to the overhead conductors and assess the performance of the DC supply system. Specific problems relating in particular, to earthing and location of surge arresters were identified. A number of options for protecting the DC system from strikes were investigated through computer simulation. The effectiveness and practicality of each of these options was assessed and guidelines for a practical solution were suggested for implementation