An assessment of the reliability of in-service gapped silicon-carbide distribution surge arresters

Although gapped silicon carbide arresters are no longer purchased by electricity authorities, they still form the majority of the very large number of distribution arresters in service in Australia and many other countries. Most of the arresters of this type are now over ten years old and many are much older. So the question must be asked-what is to be done with this ageing and outdated class of arresters? Extensive Australian studies in the 1960s had revealed that internal degradation resulting from inadequate seals was the predominant cause of failure of gapped silicon carbide arresters. This paper describes the results of a recent investigation. Electrical testing showed that after about 10 years of service, there is a marked upturn in the number of arresters with unsatisfactory insulation resistance, and after about 13 years of service, a marked upturn in the number of arresters with reduced power frequency sparkover level. Inspection of the internal components of dismantled arresters confirmed that the likelihood of significant degradation increased markedly with years of service, and was evident in almost 75% of arresters with 13 years or more of service. The authors therefore recommend that all gapped silicon carbide arresters with 13 or more years of service be progressively replaced by modern metal oxide arresters.