The initiation and growth of electrical tree in crystalline polymers are influenced by the superstructure. But, there are still many unclear points in the relationship between the tree deterioration and the superstructure (spherulites).
In order to study relationship between the tree deterioration and the spherulite, we designed the measuring apparatus which allows simultaneous observation of these phenomena. The sample was set on the stage of the polarizing microscope to make observations of the tree initiation and growth in polypropylene.
This paper reports results of some observation concerning the tree initiation and growth in polypropylene with 60Hz AC voltage. The results are as follows:
(1) Prior to the initiation of trees, a fine deterioration zone is formed on spherulite surfaces. Thereafter, the discharge is occurred along spherulite surface, and the trees occur.
(2) Tree shapes change under the influence of distribution state of spherulite.
(3) Tree initiation voltage are 5.8kV for the spherulite inside and 5.1kV for the spherulite boundary, respectively.
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