Insulation condition monitoring of hybrid switchgear

Powerlink Queensland has been a pioneer utility in the application of hybrid gas insulated switchgear (HGIS). The first complete HGIS substation was commissioned in 1999. Since then, more than 200 modules of HGIS have been installed in Powerlink's 110 kV to 330 kV substations. Based on seven years of service experience, Powerlink decided to adopt off-line monitoring of the insulation of the HGIS modules. As HGIS technology is similar to more conventional gas insulated switchgear (GIS), the current methods for assessment of GIS insulation were considered generally suitable for application to HGIS. In particular, partial discharge (PD) diagnostics based on the UHF (ultra-high frequency) method were chosen as an appropriate non-intrusive method for on-site testing. This paper describes the reasons for deciding to implement insulation condition monitoring in HGIS switchgear and the benefits of this monitoring. The different options for off-line and on-line monitoring are considered. The particular application of the UHF method in the partial discharge testing of HGIS is described. The UHF method for partial discharge diagnostics in GIS is well known. However, the specific architecture of HGIS, where the bus-bars are air insulated, presents a challenge for the practical use of the UHF technique. In order to develop this method, a series of tests in a high voltage laboratory was completed. Typical insulation defects were modelled in an HGIS switchgear module and the partial discharge fingerprint for each defect was determined. Finally, the on-site testing procedure of an HGIS substation is discussed and some examples of field testing are shown