Second Interim Report-Minimum Electrical Clearances for Substations Based on Switching Surge Requirements

The Working Group on Project 59.1 of the Transmission Substations Subcommittee of the IEEE Substations Committee is preparing a Guide for Minimum Electrical Clearances for Substations. This paper presents an interim report of tentative recommendations for clearances in substations rated 230 kV and higher, and based on switching surge considerations. Clearances for line-to-ground insulation systems have been based upon rod-to-plane switching surge test data. Phase-to-phase clearances have been based on rod-to-rod switching surge test data. Clearances are determined for a variety of switching surge levels and probabilities that the maximum transient voltage will be withstood.