Research On The Treeing Mechanism Of Silicone Rubber Under Several Coupling Fields

Electrical tree in silicone rubber material will affect the safety operation of the power cable transmission lines, which may be affected by many factors. However, it is easy to cause stress concentration with the complexity structure of cable accessories. Defects are easy to generate in prefabricated attachments during the production and transportation process. Electrical tree is easy to generate for these factors.During the brake operation, converter and lightning in the high voltage dc transmission line, it is easy to form high voltage pulses. The work environment of cable accessories will be deteriorated. In addition, high currents will generate magnetic field around the conductor in the cable transmission system, which will affect the electrical treeing processes. In some cold areas, the state of silicone rubber will change and the cable work environment becomes worse. In this paper, electrical tree is investigated by using the typical needle-plate electrode. The pulse voltage, magnetic field and low temperature environment are investigated to explore the electrical tree growth characteristic and its treeing mechanism. The main research contents and conclusions are as follows:1. Typical electrical tree is divided into three kinds in room temperature vulcanized silicone rubber with pulse voltage. They are named branch tree, bush tree and bine-branch tree. The pulse amplitude, pulse frequency and pulse polarity are investigated in order to characterize electrical tree. The patterns of electrical tree, tree length, fractal dimension, accumulated damage and tree breakdown characteristics are studied. The results show that tree characteristics are dependent on the pulse voltage.2. By applying pulse voltage and magnetic field, the effects of magnetic field on electrical tree in room temperature vulcanized silicone rubber are investigated. The typical tree is branch tree structures. With the magnetic field, the pulse amplitude and pulse polarity are investigated in order to characterize electrical tree. The effects of magnetic flux density on the tree growth characteristics are also analyzed.3. Under low temperature environment, electrical tree characteristics are studied in silicone rubber materials. The effects of low temperature on silicone rubber are investigated; it is found that there are high elastic state, crystallization state and glass state during the temperature decreasing. During the state change of silicone rubber, there are crystalline area and amorphous area. In pure crystal, molecular chains are closely arranged; pores and stress concentration are easily to generate around the edge of the uneven crystal. In the glassy state, the crystals are closely arrayed and the motion of the molecular chain becomes difficult. Results show that electrical tree growth characteristics are seriously affected by the low temperature environment.