Overvoltages at two instruments grounded at different places in a railway signal system

Various types of signal and control cables are connected to railway signaling systems, and usually those cables are comparatively long. In general, surge protective devices (SPDs) are used as a lightning-protection measure. However, certain types of cables cannot have SPDs due to a fail-safe perspective. In this study, using the Finite Difference Time Domain method and measurements, we confirmed the effects of a method proposed to mitigate overvoltage at two instruments grounded at different places in a railway signal system. The proposed method is that other spare (unoccupied) lines surrounding the control lines in a cable are connected to the ground terminals of instruments existing at both ends of the cable. We have reported the effects of the spare line use on the overvoltage, in comparison with a case of no spare line use.