How the Switching-Surge Family Affects Line Insulation

Tests were made at the Barberton, Ohio, outdoor laboratory of The Ohio Brass Company to cover a range of insulator string lengths, tower sizes, and switching-surge wave shapes, and to explore the response of line insulation to these surges. Surge-front durations of about 250μsec (microseconds) give the lowest flashover voltages. The effect of a preceding trapped line charge (bias voltage) is small but not negligible. Expected field performance under normally adverse conditions is given for line-to-tower insulation and midspan-to-ground gaps. Rod gap studies explain some of the low positive-polarity dry switching-surge flashovers.