The influence of morphology on electrical tree initiation in polyethylene under AC and impulse voltages

Influence of morphology effects on electrical properties in XLPE

“…Because of the design of the test, it is also probable that the polymer matrix in close proximity to the sharp needle electrode/polymer interface is likely to be considerably different to the bulk morphology, especially when the electrode has been inserted to the LDPE in the molten state. 7,33,34 A thin layer with a different morphology, referred to as the transcrystalline area, is believed to extend up to 1 lm from the surface before the bulk morphology take over. 33 Research on transcrystalline growth around cotton fibers in a polymer matrix has shown that the formation of a transcrystalline layer is favored at annealing conditions, 35 which would be close to the parameters in the needle insertion procedure, where the initial slow cooling rate is about 15 C/h.…”

“…7,33,34 A thin layer with a different morphology, referred to as the transcrystalline area, is believed to extend up to 1 lm from the surface before the bulk morphology take over. 33 Research on transcrystalline growth around cotton fibers in a polymer matrix has shown that the formation of a transcrystalline layer is favored at annealing conditions, 35 which would be close to the parameters in the needle insertion procedure, where the initial slow cooling rate is about 15 C/h. Although no detection of a transcrystalline layer has been made, it is highly likely that the present electrical tree inception method is inappropriate for measurements on the effect of morphology and crosslink structure on electrical tree inception voltage, as the true morphology at the needle tip cannot be ascertained.…”

Influences of Morphology on Tree Initiation in Crystalline Polyethylene Films

“…The tree, once generated, will grow with internal discharges, and eventually bridge the electrode, resulting in a complete breakdown. Some researchers believe that the amorphous region between the lamellae of spherulites and spherulites boundaries is weak in electrical resistance [3][4][5][6]. The major results from recent investigations appear to be that the tree initiation voltage is greatly influenced by crystallinity of PE [7,8].…”

“…The amorphous region between lamellae will decrease the tree initiation voltage because of the lower electrical withstand ability than in crystalline part [6,13]. Ordinarily, in the spherulites, if the thickness of amorphous region decreased, the thickness of lamellae would increase.…”

“…According to some results obtained, the diameter of spherulites in PE is proportional to the crystallinity and thus the tree initiation voltage is related with the size of these spherulites [9]. The research on the influence of lamellae on electrical tree initiation appears to indicate that the electrical tree path is virtually parallel to the lamellae, thus the tree initiation is related with the initial properties of spherulites [6,10]. Experimental results and their interpretations vary among different investigators, it is difficult to determine the relationships between electrical tree initiation and the morphology of polymers even though in PE, which has been widely studied.…”