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.