Maximum switching overvoltages on systems of 115 kV and above

NESC and OSHA provide basic minimum approach distances for workers exposed to energized facilities. These distances are based on maximum overvoltage experienced on systems as reported in the literature. There are provisions in both documents permitting a reduction in the minimum approach distance that is based on the "maximum magnitude of the transient overvoltage that can appear at the work site". That maximum depends upon the type of switching equipment installed working conditions and the surge "control or limits" utilized. This paper reviews the maximum transient switching overvoltage that can occur, when re-energizing a line with no control of the switching device and without any voltage limiting devices installed as well as the more "normal" work condition utilizing a "hold" or reclosing blocked. Finally current methods used to "control" switching impulse overvoltages are discussed.