Quantitative evaluation of lightning surge range voltage–time characteristics in high‐pressure SF6 gas

Abstract

AbstractGas‐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 SF6 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 SF6 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