EXPERIMENTAL DETERMINATION OF FLASHOVER PERFORMANCE OF CYLINDRICAL SPACERS IN N2:SF6 GAS MIXTURE UNDER AC VOLTAGES FOR NON-UNIFORM FIELDS

The gas mixture N2:SF6 has been used in gas insulated switchgears, gas insulated transmission lines and gas insulated cables for years in order to reduce the use of SF6 gas in electrical system. By taking into account the insulation performance and environmental effect, it is advised that the use of N2:SF6 gas mixture in practical to lower the SF6 gas content as far as possible. The present study is undertaken using different N2:SF6 gas mixture ratio to determine the flashover characteristics under AC voltages. In this paper the effect of floating particles, use of different insulating spacers namely PMMA, PP and NYLON and their combination forms hybrid spacers has been studied in non-uniform electric field (needle – plane) electrode configuration. The surface flashover performances of individual and hybrid spacers have been compared in N2:SF6 gas mixture. The experimental results shows that conventional spacer PMMA show better performance than the other spacers (PP and NYLON) at the gas pressure of 0.18MPa. As the gas pressure increases further the flashover voltage values slightly decreases. The hybrid spacer PMMA – PP are more effective at lower pressure than other spacer combinations. With floating particle, PP shows better flashover at lower pressure and the performance of PMMA – NYLON is much better at lower pressure.