The Development of Low-Current Surface Arcs Under Clean and Salt-Fog Conditions in Electricity Distribution Networks

Abstract

Electricity distribution networks are built to deliver increasing amount of electricity from distributed energy resources (DERs) such as offshore and onshore wind and solar farms. Aging of network assets through low-current surface discharges is becoming a great concern for the security and reliability of the distributed energy supply. In particular coastal conditions can present a challenge for overhead line insulators through the environment of salt fog. Also, onshore areas may expose power lines to clean fog and agricultural or industrial pollution. In this paper, experimental studies are conducted to investigate electrical arc formation and growth on insulators, following the testing standards in accordance with IEC 61109. Dry-band arcs in both clean-fog and salt-fog environments are compared. It is identified that arcs are much faster to develop and have greater energy in salt-fog environments, due to the lower surface resistance and resulting higher leakage current. The time from a first arc to strike, to the situation where the arc is stable on the insulator surface is identified as a potentially critical parameter in controlling aging of an insulation surface. The time from initial appearance of an arc to full stability is eight times shorter in a salt fog of 16,000 $\mu \text{S}$ /cm compared to a clean fog of $600~\mu \text{S}$ /cm. This means the very existence of a stable low-current arc is much more likely in polluted conditions. Accumulated arc energy and heat dissipation have been calculated for both fog conditions. It is concluded that aging by low-current electrical arcs tends to be more severe in salt-fog environments, so that great care needs to be taken when designing overhead lines and insulators in such areas.