Fundamental Characteristics of AC Flashover on Contaminated Insulators Covered with Ice

Abstract

The fundamental characteristics of ac contaminated flashover on iced insulators were studied for the three icing states, i.e., glaze, hard rime and soft rime, which are observed most frequently in service conditions. The results showed that thawed snow with a relatively low salt concentration can produce a salt deposit density (SDD) high enough for flashover on an iced insulator. For the same concentration of contamination liquid, average values of SDD for icing states are 5 to 9 times higher than those for icing-free conditions. The results also showed that the minimum flashover stress of the soft rime condition is 20% lower than that of icing-free conditions. For this reason, we deduced that the number density of Na atoms in the discharge space at flashover tends to become highest under the soft rime conditions.

Contribution to study of visible discharge initiation and development on the ice surface =

“…It can be seen very clearly that the critical breakdown voltage increases with increasing cooling rate. This phenomenon is thought to be related to the surface structure of the ice samples, as it was already observed in a previous observation that the surface flashover characteristic under combined icing and contamination conditions depends on the type and morphology of the ice [95]. They show that the number and dimension of enclosed air bubbles varies depending on the cooling rate.…”

“…The fundamental characteristics of ac breakdown under conditions of combined contamination and ice covering were also investigated [95]. Experiments were carried out on a rectangular physical model mounted at an angle of 30°.…”

Étude des conditions critiques de la propagation de l'arc sur les isolateurs recouverts de glace =

“…The changes in the insulating strength of a flat insulator, under different ice types (glaze, soft rime or hard rime) were studied by Sato et al [103] using ice formed by spraying NaCl-contaminated water on an insulator in a cold room. According to their results, soft rime leads to a 20%-reduction in flashover voltage compared to ice free conditions.…”

“…Lee et al [82] and Schneider [103] independently tested an insulator in the vertical, horizontal and V type positions. The V type insulator string displayed superior performance to the one observed for a vertical string under similar ice conditions.…”

“…Sato et al [103] investigated the flashover performance of a flat plate insulator covered with the three types of ice (glaze, soft rime and hard rime) formed by spraying a contaminated liquid on an insulator in a cold room. For a given concentration of NaClcontaminated liquid, the average SDD (Salt Deposit Density) value for an ice state was 5 to 9 times higher than the average SDD value under ice-free conditions.…”