Condition assessment and failure modes of solid dielectric cables in perspective

Older solid dielectric cables are now approaching the end of their life and failing. Consequently there has been a sustained effort for the development of techniques to assess the remaining life of in-service cables for the purpose of establishing replacement criteria. Because of the generally accepted belief that the failure mode is due to the aging of the insulation, these techniques have mainly focused on measuring changes in the electrical properties of the insulation. However, it has been determined that there are other failure modes associated with loss of the protective function of the jacketing material leading to corrosion and breaks in the metallic shields and poor contact between semiconductor and metallic shield, causing arcing damage and eventual failure of the cable. This failure mode is more prevalent in cables operated in a harsh chemical environment. This paper presents the results of a research program aimed at developing a test protocol that is based on evaluating the condition of all the cable components and not just the insulation. The tests were designed to evaluate the condition of jacket, extent of corrosion of the metallic shield, and degree of degradation of the cable insulation. The results are discussed in terms of correlations between the field measurement parameters and the condition of the cable, and prioritization criteria for cable replacement.