On-site dielectric testing of GIS: theoretical and practical considerations

After reviewing the primary objectives of on-site testing of GISs, (gas-insulated substations), the authors provide an analysis of practical experience in the use of several alternative test techniques in a large sample of operational GIS installations. It is observed that AC tests thus far have been the most effective. Consideration of the physical background, however, supports the inclusion also of a lightning impulse voltage test, but with the test level strictly limited in order to take account of the associated very fast transients which could arise in the event of test flashover. Recommendations for an amended on-site test approach for GIS are presented, together with comments on the implications for further research on measurement techniques