AN ASSESSMENT OF THE RELIABILITY OF IN-SERVICE GAPPED SILICON-CARBIDEDISTRIBUTION SURGE ARRESTERS

Although gapped silicon carbide arresters are no longer purchased by e lectricity authorities, they still form the majority of the very large number of distribution arresters in service in Australia and many oth er countries. Most of the arresters of this type are now over ten year s 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 So the question must be asked - what is to be done with this ageing and outdated class of arresters? Extensiv e Australian studies in the 1960's had revealed that internal degradat ion resulting from inadequate seals was the predominant cause of failu re of gapped silicon carbide arresters. This paper describes the resul ts of a recent investigation. Electrical testing showed that after abo ut 10 years of service, there is a marked upturn in the number of arre sters with unsatisfactory insulation resistance, and after about 13 ye ars of service, a marked upturn in the number of arresters with reduce d power frequency sparkover level. Inspection of the internal componen ts of dismantled arresters confirmed that the likelihood of significan t degradation increased markedly with years of service, and was eviden t in almost 75% of arresters with 13 years or more of service. The aut hors therefore recommend that all gapped silicon carbide arresters wit h 13 or more years of service be progressively replaced by modern meta l oxide arresters.