The Chaos Characteristics Analysis for Electrical Treeing Propagation in XLPE Power Cables

The electrical breakdown can be induced by electrical tree in cross-linked polyethylene (XLPE) cables. In order to study the electrical tree, the needle-plane electrode which is different from the cable in geometric configuration is usually used to simulate the defect in XLPE cable. In this paper, an actual 15 kV XLPE cable was used to test the electrical tree, its electrical stress enhancing was simulated by a metal needle defect. The growth of electrical trees was detected by the digital partial discharge (PD) measurement, and the structures of them was observed from cross and vertical section by optical microscopy. The test results indicated that the width of electrical trees on cross section is greater than which on vertical section in the voltage range of AC 12 kV to AC 21 kV because of the different distribution of electric field. The chaos analysis for the time series of PD data indicated that the propagation of the electrical trees showed the characteristics of the deterministic chaos. And its maximal Lyapunov exponent and correlation dimension of the strange attractors increased with the decrease of the fractal dimension of the trees. Therefore, it demonstrated that the random propagation of the trees is limited by the reversed electrical field, and this limitation for the bush-like trees was less than the branch-like trees. This limitation was analyzed also through the mechanism of the trees growth.