Investigation On Property And Mechanism Of Electrical Tree Of Polyethylene/Montmorillonite Nanocomposites

Polyethylene (PE) is a kind of plastic which is used widely in electrical insulation field. It has excellent insulation properties, but electrical trees will be initiated easily under long-term high electric field. Nanocomposites have the special characteristics of nano-particle's unique quantum size effect, small size effect and surface effect. At present, polymer/layer silicate (PLS) nanocomposites have become investigation focus for its excellent properties. Montmorillonite (MMT) with the layer-structure of 2:1 type is one of the most prevalent used layer silicates. Therefore, the modification of by nano-fillers has important scientific research value and engineering significance.Polymer/montmorillonite(PE/MMT) nanocomposites are prepared by melting intercalation process. Microstructure of PE/MMT nanocomposites is characterized by SEM. The results show that composites obtained are nanocomposites.The electrical treeing and partial discharge(PD) signals corresponding to characterstics of electrical tree of PE and PE/MMT nanocomposites are respectively studied by the combined test system of electrical tree initiation and PD measurement. The results show that dispersion of electrical tree is small, and most of electrical trees are thick-branch-shaped or bush-branch-shaped in PE/MMT nanocomposites obtained by melting intercalation process. Whatever under AC or DC electrical pre-stress initiation, at the voltage applied to the samples for 120min the length of electrical trees is shorter in PE sample under the same condition. The fractal dimension of electrical trees in PE/MMT sample during electrical treeing is larger, however PD is smaller and sparser than in PE sample under the same condition. The results show that PE/MMT nanocomposites can effectively restrain the electrical tree to grow. In addition, positive DC electrical pre-stress can restrain the growth of electrical tree, but negative-polarity can accelerate it.For futher Investigation on treeing-resistance-mechanism of PE/MMT nanocomposites, thermally stimulated current(TSC) spectrum was tested of PE and PE/MMT nanocomposites.It has shown in the TSC spectrum that the TSC temperature peak of PE/MMT nanocomposites fell, but the peak value increased and the peak breadth shrinked. And there is tiny current peak in the high temperature domain. The results of calculation by the initial-rise method show that there are deeper traps in PE/MMT nanocomposites. These traps can restrain the growth of electrical tree through modulating the thickness and mobility of charge carriers.