Electrical strength of towers in 500-kv design

Tests have been conducted on transmission towers to establish flashover levels of switching-surge, impulse, and GO-cycle voltages for use in the design of structures for a SOO-fcv line. The tests on the actual tower verified the adequacy of the design to withstand switching surges of 2.5 times the maximum operating voltage of 550 kv for a line constructed at an average elevation of 5,000 feet