Evaluation of the effective protection distance of low-voltage SPD to equipment

Installing surge protection devices for a low-voltage power supply is important to ensure the survival of electric or electronic devices and systems. Sometimes one group of surge protective devices (SPDs) installed on the distribution board is expected to protect all equipment supplied power by this distribution board. This equipment is connected to the distribution board by cables with different lengths, the influence of the cable length between the SPD and protected equipment on protective effects of SPD was discussed. The reflection and oscillation phenomena of the transient voltage caused by the connecting cables were analyzed, which would affect the protective effects of SPDs. These phenomena depend on the characteristics of the SPDs, the properties of the protected loads, and the length of the connecting cable. Five different types of loads and three different cable lengths have been simulated by electromagnetic transient analysis software, and their respective transient voltages across the SPD and the load were discussed in detail. The effective protection distances of SPD to equipment were analyzed for different types of loads.