Development and Performance Verification of High Resistance Semiconducting Glaze Insulators

Abstract

In case of transmission lines along the sea coast, audible noise due to partial discharges may occur from insulators when contaminated with sea salt and wetted. From the consideration to residents, insulator washing has been performed periodically, but this results in increase in the maintenance cost. As a countermeasure to reduce the audible noise, semiconducting glaze insulator (DC resistance approx. 20MΩ) has been developed and used. However, in case of a very special environment with direct spraying of sea water in seaside districts, there seems to be some risk of thermal runaway because voltage concentration on very small number of insulator units in a string is possible and it may rise the temperature of those units up to the critical point.In this paper, the thermal runaway mechanism is clarified from view point of input and output energy of the semiconducting glaze insulator under contaminated and wetted condition. The surface temperature starting thermal runaway is estimated from various experiments. As a result, the high resistance semiconducting glaze insulator, which has higher thermal runaway withstand capacity and acceptable agreeable audible noise characteristics is developed and subjected to the field evaluation.