INHOMOGENEOUS FIELD BREAKDOWN IN GIS - THE PREDICTION OF BREAKDOWN PROBABILITIES AND VOLTAGES.

An improved model for the calculation of statistical time lags in SF//6 insulated electrode arrangements for positive impulse voltage is presented. On the basis of physical considerations, the production rate of initial electrons is ascribed to the local density of negative SF//6 ions and to field dependent electron detachment. Values of negative ion densities are measured directly, while the detachment coefficient is determined by a fitting procedure to measurements of statistical time lags. The understanding of the relevant physical processes is a step forward toward an optimization of testing procedures and the judgment of their efficacy.