Effective Protection Distance of SPD in PV System Under Lightning Surge

The presence of surge protective devices (SPDs) can mitigate the overvoltage and ensure the safety of photovoltaic (PV) installations in the case of lightning strike. However, if the length of cable between SPD and the equipment is too long, the propagation of surges can lead to an oscillation phenomenon, resulting in overvoltage and protection failure. The transient circuit is established considering the transmission of lightning surge within the PV system, and the overvoltage caused by the oscillation is calculated using the circuit method. The effective protection distance (EPD) of SPD is obtained by comparing the overvoltage peak with the rated impulse voltage of protected PV string. Finally, the influence of various factors on the EPD of SPD is studied through electromagnetic transient simulations, and the results of examples prove the validity of the proposed analytical method. It is found that the EPD of SPD in PV system is related to the rated impulse voltage of PV installations, the electrical parameters of connecting cable and the
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characteristics of SPD. Increasing the number of PV strings connected to the combiner box can increase the EPD of SPD installed in the combiner. When the distance between combiner box and the PV inverter is small, it is possible to install one set of SPDs, and they are recommended to be installed inside the combiner box. Furthermore, the lightning strike point does not significantly affect the EPD of SPD.