A Critical Review of GIS On-Site Testing, Monitoring and Diagnostics Based on Recent Service Experience

Inhalt:
Gas-insulated switchgear was developed in the 1960’s, has now been in operation for more than 55 years and show a high level of reliability. Today’s design of modern GIS is highly compact regarding the size of equipment. This is combined with increased gas pressure, higher electrical stress on the electrical insulation system and increased risk of breakdown due to minimised safety factors between IEC test voltages and withstand voltages. Defects in the electrical insulation system, such as protrusions or particle on insulation, are becoming increasingly dangerous, and recent experience with 420 kV GIS during on-site testing and in service shows failures due to insufficient integrity of the insulation system. This requires an improvement in the PD detection sensitivity of Partial Discharge Monitoring systems to e.g. 2 pC for protrusions and, in addition, the Cigre Sensitivity Verification Procedure must be performed correctly. Innovative PD methods such as optical PD measurement can also contribute to improved PD detection. On-site tests should also be carried out again with an OLI test until the required PD measurement sensitivity is achieved.