Development of high-resistance semiconducting glaze insulators

As a countermeasure to reduce the audible noise, we have developed semi-conducting glaze insulators (DC resistance approx. 20 Mohm) and used. However, in case of a very special environment with direct spraying of sea water, there seems to be some risk of thermal runaway. In this paper, we clarify the thermal runaway mechanism from view point of input and output energy of the insulator under contaminated condition. The surface temperature starting thermal runaway is estimated from various experiments. As a result, we develop the high resistance semi-conducting glaze insulator, which has higher thermal runaway withstand capability and acceptable audible noise characteristics. We eventually put it into practical use, develop faulty insulators detector at the same time.