Diagnostics for gas insulated substations

A gas insulated substation could fail if it were to contain a defect such as a free metallic particle or stress-raising edge on an electrode. However the defects may be detected because they generate partial discharges before breakdown occurs. Various detection methods have been tested, and most success achieved with either acoustic transducers to detect sound waves from the discharge, or electrical couplers to pick up the ultra-high-frequency (UHF) signals generated inside the GIS chambers. In both cases further information, such as the repetition rate of the discharges and the points at which they occur on the power frequency wave, enables the defect to be identified and the risk of complete breakdown assessed. In the future, increasing use will be made of expert systems to interpret the discharge data automatically, especially when the GIS is monitored continuously. It is also expected that monitoring will be extended to include the performance of circuit breakers and other plant in the GIS