GIS insulation co-ordination: on-site tests and dielectric diagnostic techniques. A utility point of view

This paper summarizes the Electricite de France experience with insulation coordination of gas-insulated substations (GIS). After a review of the insulation coordination practice, mainly dealing with fast front overvoltages and the one minute AC test, some results of the on-site test procedure applied for 30 years are presented and related to the insulation co-ordination practice. The in-service return of experience dealing with dielectric failures is analyzed. The dielectric diagnostic techniques now available are briefly presented with their possibilities and limitations. According to this survey, the expectations of EDF from these diagnostic techniques as well as the new on-site test and online monitoring tendencies at EDF are presented.