Study of Polarization Sensitivity of UHF Sensor for Partial Discharge Detection in Gas Insulated Switchgear

Polarization sensitivity of ultrahigh-frequency (UHF) sensor for detecting partial discharge (PD) activity in gas insulated switchgear (GIS) is studied using a tapered planar spiral (TPS) antenna. The TPS antenna with coplanar broadband microstrip line balun was optimized for circular polarization (CP) over 0.5-3.5 GHz. The fabricated TPS antenna with protective cover and cavity backing has a unidirectional radiation pattern, a -10 dB bandwidth (BW) of 0.5-3.5 GHz, and an axial ratio (AR) < 3 dB over 0.57-3.5 GHz. The polarization sensitivity of TPS to detect PDs was studied for Corona and particle movement (PM)-induced PDs in L Section of a metal encapsulated GIS setup. PD induced UHF measurements of circularly polarized TPS for 0°, 90°, and 180° orientations inside L-GIS gathered before and after L bend were compared with a linearly polarized (LP) UHF antenna with comparable gain and receive pattern. PD measurements gathered after L bend show nearly twofold enhancement in signal amplitude for the TPS compared to the LP sensor. The reduction in the ratio of UHF sensor amplitude after and before L bend between 0° and 90° sensor orientations was less than 8% for the TPS compared to 19%-27% observed for the LP sensor. It is concluded that UHF sensor with broadband CP is desirable for PD sensing in GIS.