Unit voltage duties in long suspension insulators

POTENTIOMETER measurements^∗ were made of the maximum and average voltage duties occurring in strings made up of 10-inch cap and pin type units wherein the numbers of the units were varied from 2 to 20. The numbers of units in the string and their corresponding maximum to average voltage duty-ratios thus obtained were used to locate curve II in Fig. 1. The increase in the duty-ratios is small for the shortest string of two units, it accelerates rapidly as the string is lengthened to 7 units and thereafter it remains constant at the rate of 0.09 per unit added from 7 to 20. Such increase is low and accelerating in short strings of from 2 to 7 units while it is high and constant in long strings of 7 or more units.