Issues in defining a type test for GIS disconnectors

A type test for gas-insulated substation (GIS) disconnectors is discussed. The author introduces the complexities of the topic, provides a summary of the technical background, poses the questions which must be addressed, and discusses the technical and commercial considerations which influence the approach toward a solution. The purpose is to provide a systematic context in which the problem can be considered and give the interested nonspecialist the background necessary to provide input to the process of standard preparation and to judge the quality of the result. GIS disconnectors typically fail during normal operation, not as a result of an abnormal system stress, and disconnectors are operated frequently. As a result, any type test must assure that the probability of failure per operation is in the range of 0.001%. Three possible approaches to type testing are identified, two of which appear to be realistic alternatives. Analysis of these alternatives results in the conclusion that the required test parameters cannot be defined from first principles. the parameters will probably be based on past experience and defined so that disconnectors which have not been adequately reliable would not pass the type test while those which have been reliable will pass