Comparisons of in-service and laboratory failure modes of metal-oxide distribution surge arresters

Descriptions are given of the findings from tests and inspections of arresters withdrawn from service, the results of laboratory studies with multipulse lightning currents and high temporary overvoltages, and comparisons of in-service and laboratory failure modes. It is shown that gapped metal-oxide arresters are vulnerable to degradation from moisture ingress in the field and that the main causes of gapless arrester failures in the field and in the laboratory include very high temporary overvoltages and lightning strikes with multiple strokes