Nano-composite polymeric insulating material of mixed addition for control of treeing deterioration

A purpose of this study is to establish a basic concept of originally designed nano-composite for long term high endurance to electrical treeing deterioration. The nano-composite designed by us was prepared by a mixed addition of azobenzoic compound and Al₂O₃ nano-particle into LDPE. Through tests, 4´-hydroxyazobenzene-2-carboxylic acid (hc_Ab) was selected from six kinds of azobenzoic compounds as a candidate which will provide the long term performance. Experimental results under a room temperature with test materials before an accelerated aging procedure showed that when `hc_Ab´ was adopted as a compound for the mixed addition, tree initiation voltage was increased to about 1.2 times higher than that for a single composite with `Al´, which was about 1.8 higher than that for basic polymer (LDPE); An incubation time (a period of time from voltage application to tree appearance) was almost 1000 times longer than that for the base polymer under the constant applied voltage. It was experimentally suggested that absorption of electron´s kinetic energy can be obtained by excitation of `hc_Ab´ and cohesion of nano-particles can be controlled in the bulk of the nano-composite using `hc_Ab´, which will provide the high performance for the tree control. A long term endurance test is carrying out under high temperatures, 87 °C, 92 °C and 95 °C. Properties for evaluations of the endurance are change in weight, dissipation factor and UV absorption characteristics. After 2500 h from a start of aging, a change of 0.5 wt% in weight was detected with the mixed addition under 95 °C. By contrast, the change of the basic polymer was 2 wt%. The incubation time of the mixed addition was kept almost unchanged from an initiation stage.