Characteristics of VFTO Generated in a GIS with $SF_6-N_2$ Gas Mixture as the Insulating Medium

摘要

This paper deals with the experimental characteristics of VFTO in pure $N_2$, pure $SF_6$ and $SF_6-N_2$ mixtures. The investigations are performed using a laboratory model bus duct. A capacitive type voltage sensor was used to measure the VFTO peak magnitudes and temporal characteristics. Measurements were carried out in $N_2$, $SF_6$ and $SF_6-N_2$ mixtures wherein the $SF_6$ concentration was varied from 10% to 40% over a pressure range of 1 bar to 5 bars. The results from the VFTO characteristics obtained for $SF_6$ and $SF_6-N_2$ mixtures show similar trends in variations. The levels of surge peak magnitudes are less than 2 p,u. for all the cases considered in the experimental pressure range. In $N_2$, the peak magnitude remains almost constant with increasing pressure but for pure $SF_6$, it increases almost linearly with pressure. On the other hand, for the gas mixtures, the difference in peak magnitudes is not significant at pressures between 2 to 4 bars. The occurrence of corona stabilization during breakdown of the gap is thought to be the cause for this behavior.