Dynamic potential distributions of surface discharge in silicone gel

Abstract

Silicone gel is widely used to encapsulate power electronic circuits. It is known that the weakness of this insulation system is the surface discharges between gel and substrate. These discharges give rise to the growth of cavities in gel, which may lead to eventual failure of the insulation. Despite the fact, surface discharges in gel has not yet been studied enough. In order to clarify the nature of streamers in the cavity and relation between streamer propagation and charge accumulation at the interface of the cavity, the relation between apparent charge, light emission, motion of the cavities, and dynamic potential distribution of surface discharge in silicone gel was investigated. The results showed that conductive streamers initiate at the electrode, propagate through the cavity and accumulate charges on the cavity surface. In addition, it was confirmed that conductivity of the cavity surface is low.

Electrical shielding of MV/MF transformers subjected to high dv/dt PWM voltages

“…This value, which is close to the critical field in air [17], can lead to surface discharges (creeping with tangential field). Such discharges damage the insulation, distort the potential distribution, and can lead to a flashover [19], [26], [27]. The triple points, i.e.…”

Analysis of electrical tree inception in silicone gels

“…In [14,15], the tests performed followed a classical procedure employed in liquids, with the aim to evaluate the streamer inception (streamer is a term commonly employed for the propagating breakdown structure in liquids) and to compare the behavior observed in the gels with that of silicone oil. In [16,17], the experiments focused on lower AC voltages, highlighting the formation and growth of string of bubbles having the shape akin to an electrical tree in a solid insulator (therefore, referred to as electrical trees, indifferently from the case of solid dielectrics). The tree growth and structure where compared with that of the elastomer by means of their fractal dimension.…”

“…All the studies concluded that, regardless of the self-healing behavior of silicone gels, a continuous voltage application leads to the formation of discharge-supporting electrical tree structures [13,16,17], the skeleton of which is permanent [17] (i.e. the material is irreversibly damaged).…”

“…the material is irreversibly damaged). These structures propagate inside the dielectric from a needle electrode [13,16,17] and can eventually lead to electrical breakdown. In bulk silicone gels the propagation of the tree structure is preceded by an inception stage in which a discharge supporting cavity is formed at the needle electrode by either bond-breaking or plastic deformation or both, i.e.…”

On the nature of surface discharges in silicone-gel: Prebreakdown discharges in cavities

“…In the former paper, (1) we have proposed an analyzing procedure for discharges in gel based on motion observation of cavities induced by discharges, and applied to some characteristic motions of the cavity [7], and (2) measured the dynamic potential distributions of surface discharges in silicone gel on glass substrates [8]. The aim of this paper is to confirm validity of the assumption we have made, to investigate discharges on ceramic substrates which are generally used for power modules, and to summarize the features of surface discharge in gel under AC voltage.…”