Discharge Phenomena of the Insulator Assembly and Occurrence of Critical Cascading Flashover Phenomena

Abstract

This paper describes conditions for an occurrence of cascading flashover phenomena on the insulator assembly with the use of a high voltage transmission line by experiments in a laboratory room. The 154 kV suspension insulator assembly is employed as testing apparatus which consists of a chain of 9 standard suspension insulators equipped with an arcing horn. In the experiments, the apparatus is separated into two parts consisting of a bare insulator chain and a pair of arcing horns. The lightning impulse with positive polarity or negative are applied to the test pieces, and the over-voltage is used in those tests. Thus, the creeping flashover occurred with short lag time. The V-t curves and the 50% cascading flashover voltage were obtained and the prebreakdown phenomena were observed from the tests, then, it is concluded that the critical cascading flashovers occur with short time lag (T₀＝1.8 μ sec. or less) and a high steepness (1833 kV/μ sec. or more), and corona on the insulator surface starts from negative side electrode.