A Method to Localize the Axial Position of Partial Discharges in GIL by Gas Sensors

This article proposes a novel method to realize the partial discharge (PD) localizing function of gas sensors in gas-insulated transmission lines (GIL). First, the diffusion characteristics of decomposition products were studied. The Fuller-Schettler-Giddings (FSG) model was corrected to obtain decomposition products diffusion coefficients in high-pressure SF6. The finite element method (FEM) calculated the temperature rise, convection, and diffusion of decomposition products in GIL. With the relationship between the concentration variation and positions, a PD defects location method was proposed. The results indicate that the decomposition products would diffuse rapidly in the radial direction with the convection. Gas diffusion at the top of the GIL was faster than that at the bottom. Hence, the gas sensors were suggested to be set at the top of GIL. The axial diffusion was much slower and mainly affected by the temperature and diffusion coefficient. For a long GIL unit, the diffusion of decomposition products could be simplified to 1-D. In diffusion, the delay of the product concentration is negatively correlated with the square of the distance. That quantitative relationship could be used for localizing PD by the concentration increase delay detected by the sensors on both sides of the defect. The localization error would decrease with the increase of diffusion coefficient (rate) and prolonged monitoring (diffusion) time. The accuracy of the localization would also increase when the defect is close to the midpoint of the sensors.