New PD sensor techniques for highly pressurized dry air-insulated systems and an alternative method to CIGRE sensitivity verification procedure

With the development of gas insulated switchgear (GIS) utilizing dry air as an alternative insulating gas to SF6, monitoring technologies for partial discharges (PD) have contributed to the reliability of the GIS and have become increasingly important. However, research and reports concerning PD characteristics in dry air are limited. In particular, sufficient knowledge regarding PD diagnosis under high-pressure dry air conditions is required. In this study, PD characteristics in high-pressure dry air are investigated to validate the applicability of the current Ultra High Frequency (UHF) detection method and to confirm that PD characteristics comparable to SF6 are observed under high-pressure dry air. By utilizing the obtained PD characteristics in high-pressure dry air, optimization of PD sensors is performed. It is confirmed that the UHF method is effective in high-pressure dry air, and that PD sensors with an extended bandwidth based on the PD characteristics under dry air exhibit superior performance relative to conventional sensors. Furthermore, regarding the sensitivity verification method for applying a UHF partial discharge monitoring system to GIS, the effectiveness of the CIGRE TB654 method (CIGRE method) [1] is confirmed in dry air by employing simulated pulses generated based on actual discharge source. Since a pulse generator is constrained by losses of measuring cables and export controls, alternative sensitivity verification methods by circuit simulations and numerical analysis using the data acquired with network-analyser are proposed to supplement the CIGRE method. The scattering parameters were measured for the test GIS, and results from circuit simulations and numerical analyses were found to agree well with the measured data.