Monitoring of the dielectric strength of the air/SF

This paper investigates the dielectric properties of various air/SF6 gas mixtures based upon a cylindrical spacer model with adhering particle on the surface under homogeneous field conditions. The investigation involves a comparison with pure SF6. The flashover field strength for clean and particle contaminated spacer surface under lightning impulse (LI) and alternating voltage (AC) stress is determined. The results of the investigations show the sensitivity of air/SF6 gas mixtures to conducting particles on spacer surfaces for gas pressure up to 1000 kPa. Moreover, the correspondence between pure SF6 and air/SF6 gas mixtures for AC and LI flashover field strength range from 50 to 178 kV/cm is determined. Conclusions are drawn about the ability of air/SF6 gas mixtures to serve as technically efficient media for long Gas Insulated Transmission Lines (GITL). The results shed light on the issue of the SF6 reduction and the particle detectability in GITL