Full-Scale Tests for the Allegheny Power System 500-kV Tower-Insulation System

Switching surge, impulse, and 60-cycle tests performed on the APS 500-kV tower-insulation system proved the adequacy of the design which consisted of twenty-four53/4 X 10-inch insulators in V-string configuration with an 11-foot 2-inch minimum strike distance. The minimum switching surge withstand voltage is 965 kV. Minimum impulse critical flashover voltage is 1890 kV, and the minimum 60-cycle flashover and withstand voltages are 707 kV and 660 kV rms, respectively. The switching surge test results from the full-scale tower agreed closely with those predicted from simulated tower-insulation tests. The switching surge flashover probability curve tends to follow the equations for a normal cumulative distribution curve to about the 2 to 5 percent probability level, whereas previous test results showed correlation only to the 5 to 10 percent probability level.