Weather and its Effect on Air Insulation Specifications

Using weather statistics from 10 USA weather stations, the statistical distributions of relative air density, δ, humidity correction factor, Hc , and δ/Hc are determined to be best approximated by Gaussian distributions. The wind speed distribution is best approximate by a Weibull distribution. Regression of δand δ/Hc with altitude shows a significant correlation. Using these distributions and the parameters of these distributions, it is shown that the standard deviation of δand δ/Hc need not usually be considered. Reductions of BIL aid BSL for air-insulated stations and the required increase of strike distances for transmission lines as a function of altitude are presented. The effect of wind is shown to result in design swing angles considerably less than that given in standards.