PREVENTIVE MAINTENANCE SYSTEM WITH A DIFFERENT GAS INJECTING FACILITYFOR GIS

A preventive maintenance system for gas-insulated switchgear (GIS) has been developed, which detects signs of trouble and prevents breakdown s in service. The system constantly monitors UHF signals, which are ge nerated by partial discharges(PDs) and propagate in the GIS, by using couplers built into the apparatus. The PDs are detected at high sensit ivity (5pC) and located according to the attenuation of the signals. T hen the system injects a different gas into the section where PDs are occuring and improves the dielectric strength. This prevents faults in service and allows remedial actions to be taken with less urgency. By injecting a small quantity (5-10%) of c-C4F8 into the GIS, dielectric strength is raised more than 20%. A preventive maintenance system wit h a facility to inject a different gas was constructed for a full-scal e GIS model. The system detected and located PDs, and automatically in jected the different gas to improve the dielectric strength.