Effect of repetitive rates of impulse voltage on electrical treeing in epoxy and barrier composited insulations

Electrical treeing is regarded as one of the most significant mechanism for dielectric breakdown in polymeric materials of high voltage equipment. For wind turbine generator (WTG), the insulation system would withstand the repetitive square waveform impulse electric stress as the application of the invert unit, which would promote the growth of electrical tree. In this paper, the effect of repetitive rate of the square waveform impulse voltage on electrical tree propagation in insulation composited with epoxy resin and barriers were investigated. Two kinds of the most common insulation tapes/films, the polyimide film and glass fiber reinforcing mica powder tape, were chosen as the barrier materials in this paper. The electrical tree experiments were conducted under the impulse voltage with the repetitive rate of 2, 4 and 8 kHz. The experimental results indicated that higher repetitive rate would promote the propagation of electrical tree by increasing the number of discharges in the channel. Near the barrier, the gradient of transverse length over the number of cycles increased fastest at 8 kHz, while at 2 and 4 kHz, there is no significant difference. For two kinds of barrier material, glass fiber reinforcing mica powder tape could suppress the electrical tree extension effectively, which might be due to the stronger bond between the epoxy resin and the barrier.