Toeplers spark law in a GIS with compressed SF/sub 6/-N/sub 2/ mixture

This paper deals with the experimental measurements and analysis of the formative time lags to breakdown and an estimation of the Toeplerʹs constant for gas gaps, under the application of 50 Hz AC voltage. The experiments were carried out in a 145 kV gas insulated system (GIS) bus duct with pure N/sub 2/, pure SF/sub 6/ and SF/sub 6/-N/sub 2/ mixture as insulating media. The formative time lags to breakdown in the gas gaps were measured using a fast response capacitive sensor. Toeplerʹs spark law has been used to explain the breakdown phenomenon in the GIS and the values of Toeplerʹs constant (k/sub t/), which gives an estimation of the formative time lags, were determined. Results show that the formative time lags vary inversely with gas pressure and the gas mixture concentrations for two gaps studied (0.46 mm and 0.61 mm). In the case of another gap (0.20 mm), the variation in the formative time lags with pressure as well as SE, concentration in the mixture has been found to be negligibly small between gas mixtures, although significant variation can be seen between pure SF/sub 6/ and pure N/sub 2/. Toeplerʹs constant, k/sub t/, increases with gas pressure as well as SF/sub 6/ concentration in the mixture for the gaps studied. Hence, k/sub t/ is a function of the gas pressure and the concentrations of SF/sub 6/ in the gas mixture for the above-mentioned gaps.