Quantitative evaluation of lightning surge range voltage–time characteristics in high‐pressure SF 6 gas

Gas‐insulated switchgear (GIS) is subjected to very fast transient overvoltages such as lightning surges or disconnector switching surges. Therefore, the sparkover voltage and time ( V − t ) characteristics of SF 6 in a very short time range of less than $1\ \mu \hbox{s}$ are of great interest from the viewpoint of insulation design and coordination for a GIS. This paper describes the V − t characteristics of SF 6 at a gas pressure of 0.5 MPa using a steep‐front square impulse voltage under a quasi‐uniform field gap and presents a quantitative evaluation of the V − t characteristics for a nonstandard lightning impulse voltage. In the case of a square impulse, the V − t characteristics of positive polarity were observed to be almost flat over a long time range from 80 ns to $10\ \mu \hbox{s}$ , and rose steeply over a short time range from 80 ns down to 20 ns. For negative polarity, the V − t characteristics exhibit a gentle rise from 200 ns down to 40 ns. In the estimation of V − t characteristics, the equal‐area criterion parameters were quantitatively estimated using the square impulse. For a nonstandard lighting impulse, we found that application of the equal‐area criterion with these parameters for the nonoscillating impulse and oscillating impulse of up to 5.3 MHz as a model of lightning surge and disconnector switching surge is possible. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(4): 8– 17, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20309