Minimum Line-To-Ground Electrical Clearances for EHV Substations Based on Switching Surge Requirements

During the past several years, considerable test data on the switching surge strength characteristics of air gaps with various electrode configurations has been reported by many investigators. This paper reports on a comparative study of the data in the EHV system voltage ratings of 345, 500, and 765 kV. The approach to the final recommendations recognizes the extreme expense necessary for thorough and complete testing of all electrode configurations which might occur in substation designs. Consequently, an effort has been made to generalize these variables and to provide data which will satisfy the most severe case.