Effect of Treeing Test Condition on Voltage Endurance Coefficient for XLPE Cable Insulation

The voltage endurance coefficient of solid insulating materials can be determined by electrical treeing tests, and some influencing factors on the measurement are investigated in this paper. Treeing tests are performed on XLPE insulation specimens of 110 kV AC cables with a pin-plane electrode system. The needle inserted has a pinpoint angle of 30 degrees, and the pin-plane distance is 2mm. The times for electrical trees to initiate at progressive voltage are recorded and statistically analyzed. The corresponding initiation voltage is determined to be V-0. In the following constant voltage test at V-0, the tree initiation times are also recorded. By the residual voltage method, the voltage endurance coefficient can be calculated according to the tree initiation times at progressive and constant voltage. Effects of different test conditions are investigated, including the tip curvature radius of needle electrode and the rate of voltage rise in the progressive voltage test. Two tip radii and four rates of voltage rise are applied and the results show that the voltage endurance coefficient n(t) with the tip curvature radius of 10 mu m is larger than that with 5 mu m, and n(t) decreases along with the increase of voltage rise rate. After the analysis of influencing factors, an applicable test condition can be recommended, and this will contribute to a better evaluation of the electrical aging performance for cable insulation.