Comparison of electrical tree propagation in epoxy composite insulation for WTG under repetitive impulse and AC stresses
The composite insulations consisting of epoxy resin vanish and barrier material are widely used in the insulation system of wind turbine generator (WTG). The insulation system would withstand either the repetitive impulse or the AC stress, and electrical treeing is thought as one of the main contributing factors to the degradation of polymers. In this paper, electrical tree tests in composite insulation system under the repetitive impulse voltage as well as AC voltage were carried out. The polyimide film, mica powder tape strengthened with polyester film and mica powder tape strengthened with glass fiber were chosen as the barrier materials, respectively. In order to make comparison, the tests were conducted under the same peak value of 10 kV for these two types of voltage waveform. The microscopic photographs of electrical tree inception and propagation were recorded during the whole treeing processes, in particular near the barrier interface. The results indicated that under the repetitive impulse voltage, by comparing of AC voltage, the electrical tree performed much shorter inception time, greatly quicker radial growth rate, slower extension rate along the barrier interface and further transverse extension length. Also the insulation system filled by the barrier of mica powder tape strengthened with glass fiber behaved more excellent than other barrier materials in endurance of electrical tree under both AC and the repetitive impulse voltage.