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.