Partial discharge measurements in underground distribution cable joints

The possibility of diagnosing properly electrical equipment, before an actual failure occurs in service, has always captivated utility personnel. In underground distribution, often work needs to be done in the proximity of live cables and accessories; these are in an unknown state of degradation and therefore, safety cannot be guaranteed to the workers. PD diagnosis was then the chosen approach to increase the level of confidence regarding work on underground cables and accessories. However, a decision threshold (under which no work should be allowed) remains to be established. This paper reports on a series of accelerated aging tests designed to find an actual value for this threshold; using a portable PD detector developed by our company, workers will be helped in making a decision whether or not to go ahead, by taking into consideration the suggested threshold values found in the lab