Effective Protection Distances of Low-Voltage SPD With Different Voltage Protection Levels

If surge protection devices (SPDs) are installed without consideration of the concept of lightning protection zones, the equipment to be protected might be damaged despite the correct energy coordination of SPDs. This damage is induced by the reflection phenomena on the cable connecting an external SPD and the load protected. These reflection phenomena depend on the characteristics of the output of the external SPD, the input of the loads, and the cables between the load and the external SPD. Therefore, the SPD has an effective protection distance under the condition of the specific load and the specific voltage protection level of SPD. In this paper, the equipment with different load characteristics and SPDs with different voltage protection levels are analyzed combinatorially under the operation of the surge combination wave. The influence of voltage protection level on the effective protection distance is discussed. Moreover, the effective protection distance of the SPD with the same parameter in a different voltage protection level is also analyzed in detail. The analyzed results show that the effective protection distance would be very long if the impedance of equipment is close to or smaller than the characteristic impedance of the connecting cable.