Factors affecting determination of the minimum approach distance

The purpose of this paper is to review the factors, which influence the accuracy of the calculations, used to determine minimum approach distances (MAD) used by electric utilities in the United States. Working standards are established to assure that no flashover will occur at the work site with workers present. To obtain the minimum approach distance required, it is first necessary to determine the maximum electrical stress (transient overvoltage-TOV) that can reach the work site and then to determine the minimum distance that must be maintained to withstand that electrical stress. This paper reviews the factors that affect the determination of the withstand voltage of air gaps at the work site, and the factors that determine the accuracy of the electrical characteristics of air gaps as measured in the laboratory.