The mechanism of the barrier effect in solid dielectrics

Abstract

This paper presents results of a study of the barrier effect in solid dielectrics in uniform and highly inhomogeneous electric fields. The influences of various factors such as mechanical strain, the position of the barrier in gap, space charge, the permittivity and the conductivity gradient both on the breakdown voltage and breakdown time in the uniform field and on the tree-initiation time in the strongly inhomogeneous field were investigated. Application of barriers with high permittivity may result in a significant increase in not only by virtue of there being an increase in the tree-growth time but also because of an increase in . It was discovered that the re-distribution of the field in the sample volume at the stage of initiation of failure plays a major role in the barrier effect. An analysis of existing models of the barrier effect is presented.

Effect of the Mechanical Strain on the Treeing Phenomenon

“…At this stage the tree channels can develop even backwards compared with the force lines direction of the external electric field along the boundary between the neighboring isochromatic lines ( figure 11). The boundary between the neighboring isochromatic lines in this case will act just like the interface of two dielectrics with different permittivities in a capacitively graded HV insulation [6,7]. …”

“…For the macroscopic inhomogeneous dielectrics [6,7] the interface between two dielectrics with different characteristics may play the role of these inhomogenieties. On manufacturing the samples by extrusion, hot pressing and molding method, the initial state of the samples depends on the melt flow direction and cooling rate.…”

On the barrier effect mechanism in inhomogeneous dielectrics

“…The condition for the more uniform distribution of energy in the layers may be written just like for the [6]: it the more difficult to remove from this condition of dynamic equilibrium with increase y~ [3,4]. voltage when @Vb or the increase of duration of the induction stage preceding the inception of the incomplete breakdown channel (a tree) when V<V, [3,4].…”

“…voltage when @Vb or the increase of duration of the induction stage preceding the inception of the incomplete breakdown channel (a tree) when V<V, [3,4].…”

“…The barrier effect found by Marx and Rozer [1,2] when studying discharges in air gaps during the 1930's is observed irrespective of the medium's phase state (gaseous, liquid or solid), the voltage type (DC, AC or impulse), electrode configuration (plane-plane or needle-plane) and interelectrode distance (millimetre, centimetre or decimetre range). The barrier effect in practice is usually used in insulating gaps with divergent electric field to increase V,, the time to breakdown ( 5 6 ) or the treeinception time [3-51. In spite of a wide practical usage of this phenomenon, the mechanism of the barrier effect is still not known, as shown earlier [3]. In our previous paper we represented a new phenomenological model of the barrier effect in the divergent field [6].…”