Effect of the Mechanical Strain on the Treeing Phenomenon

Abstract

The influence of the mechanical strain on the tree inception and growth in polymeric dielectrics such as polymethyl methacrylate, polystyrene and polycarbonate was studied in this work. The tree inception and growth process in transparent dielectrics was monitored by the optical method in white and polarized light in the divergent field under AC voltage. It has been found that the tree-inception time and the tree-growth time are dependent on a residual mechanical strain in the vicinity of the needle tip and in the sample volume. The tree inception-time may be increased by means of the control of the mechanical strain in the vicinity of the needle tip. Not only the treeinception and growth time but also the tree shape depends on residual mechanical strain.

Propagation of Electrical Trees under the Influence of Mechanical Stresses: A Short Review

“…This implies that the residual mechanical strain -formed during the manufacturing process-plays an important role. The conclusions of [51] are in qualitative agreement with those of [43]. The conclusions of [51] were confirmed with polycarbonate samples in a later publication [52], where it was pointed out that the melt flow directions and the fringe patterns may influence the direction and propagation of electrical trees.…”

“…The conclusions of [51] are in qualitative agreement with those of [43]. The conclusions of [51] were confirmed with polycarbonate samples in a later publication [52], where it was pointed out that the melt flow directions and the fringe patterns may influence the direction and propagation of electrical trees. An indirect evidence of the above is offered in [53], where an investigation of the electrical trees in outer and inner layers of different voltage rating XLPE cable insulation indicated that the growth rate of electrical trees in a 66 kV cable is much larger than that in the higher voltage rating cables.…”

“…Internal residual mechanical strain was studied in [51], where the way of manufacturing of transparent insulating materials -polymethyl methacrylate (PMMA), polystyrene (PS) and polycarbonate (PC)-and its influence on electrical treeing propagation with divergent electric fields was investigated. It was reported that electrical treeing stems from micro-cracks in the vicinity of the needle electrode, and in fact from its lateral side and not from the needle tip.…”

Effect of the melt flow direction on the treeing process in polymeric insulation

“…In addition, the performance characteristics of insulation articles can affect not only technological parameters but also polymer processing methods. For example, in the production of articles by pressure die casting, the distribution of the residual mechanical stress influencing treeing can depend greatly on the polymer melt flow direction [7,8].The purpose of the present work was to study the effect of the melt flow direction on the space-time characteristics of treeing in polycarbonate in a highly inhomogeneous electric field.Experimental Technique. Samples with a point-plane electrode system were made of polycarbonate by pressure die casting in specially developed die molds.…”

“…In addition, the performance characteristics of insulation articles can affect not only technological parameters but also polymer processing methods. For example, in the production of articles by pressure die casting, the distribution of the residual mechanical stress influencing treeing can depend greatly on the polymer melt flow direction [7,8].…”