On the role of transformer grounding and surge arresters on protecting loads from lightning-induced voltages in complex distribution networks

•Lightning overvoltages on loads connected to complex LV networks are investigated.•Lightning-induced voltages and transferred lightning surges are both studied.•Improving the transformer grounding does not assure load protection.•Improving the transformer grounding can in some cases increase load overvoltages.•Surge arresters at the transformer secondary are inefficient at protecting loads.

This paper presents a study of overvoltages caused by cloud-to-ground lightning strikes on loads connected to a complex low-voltage distribution network. The importance of the transformer grounding in the resulting load overvoltages is discussed for two different lightning events. These events emphasize either the induced-voltage component or the surge transference through the distribution transformer as the main source of overvoltages on the connected loads. A brief discussion is also presented on the efficiency of low-voltage surge arresters in protecting loads connected to complex low-voltage networks. The obtained results indicate that the effectiveness of improving the transformer grounding and of installing surge arresters at specific points of the low-voltage network is limited in terms of load protection if a complex network topology is considered. In some cases, especially for a lightning strike close to the low-voltage line, improving the transformer grounding can even increase load overvoltages.