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

A method has been developed for estimating line-to-ground and phase-to-phase clearances to withstand switching surge voltages in substations. Clearances have been calculated for standard system operating voltages through 500 kv with an assumed switching surge magnitude of 2.8 times the maximum line-to-neutral crest voltage. Consideration has been given to the simultaneous occurrence of opposite polarity switching surges on adjacent phases. Clearance values will be verified by testing programs before being recommended for design purposes.