UHF PD signal transmission in GIS: Effects of 90° bends and an L-shaped CIGRE step 1 test section

When applying radio-frequency (RF) techniques to measure and monitor partial discharges (PD), the CIGRE `sensitivity verification' recommendation details a methodology for achieving a specified equivalent PD charge sensitivity for the combination of RF PD sensors and the measurement or monitoring system installed in a gas-insulated substation (GIS). The recommendation allows some flexibility in the GIS set-up used to perform the test. For the work covered in this paper, second in a series, a CIGRE step 1 laboratory test was conducted using an `L' -shaped section between sensors 'C1' and 'C2', in order to present a more challenging propagation path between them. RF network analyzer (RFNA) measurements and finite-element modeling (FEM) were performed on the section and compared. The RF propagation properties of GIS sections with similar topologies in both lab and field were investigated through both models and measurements and these results compared with prior work in the field. Refinements to FEM modeling techniques result in a closer match to actual measurements, but an exact match probably remains out of reach. We discuss these results and our recent observations, the implications for PD sensor placement to satisfy the CIGRE recommendation, and outline anticipated next steps.