Limiting the number of the most severe voltage sags in rural medium voltage networks

In Finland during summer time, lightning may cause a considerably high number of short interruptions and voltage sags. In case of lightning, the overvoltage protection of power distribution transformers has an important role. In case of special concern of voltage sags, the means to limit the short circuit faults causing voltage sags should be focused to the neighbourhood of the primary (110/20 kV) substation. To contribute this matter, this paper presents results of a study where spark gaps were replaced with externally gapped metal-oxide surge arresters near the primary substation. As well the theoretical studies as measurement results encourage to carry on with such investments.