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Long-term aged performances of stator insulation for wind turbine generator under repeat pulse voltage

The power inverter between the wind turbine generator and electrical grid is commonly used for adjusting or converting the generator frequency and voltage to the grid. The stator or rotor insulation of generator will endure the step repeat pulse voltages. It has become important to evaluate the stator insulation of wind turbine generator under repeat pulse voltages. Firstly, the lab test setup with the repeat-pulsed voltage up to 10kV and frequency up to 20kHz was established, and the full sized specimens of stator insulation for megawatt direct-driven permanent magnet generator were prepared in this paper. Under the different applied voltage, from 4kV to 6.5kV, the electrical ageing or voltage-endurance testing of specimens at a constant temperature were carried out. The ageing duration was from 100hrs to 5000 hrs. During the ageing process, the ageing characteristic parameters of stator specimen were measured periodically, which included the dissipation factor, capacitance, insulation resistance, partial discharge inception voltage and corona discharge inception voltage. The relationships between the ageing characteristic parameters and ageing duration have been obtained, and the residual breakdown voltage of specimen was taken also. Some of aged specimens, if failed, were examined by means of dissection in the area around the insulation puncture in order to identify the failure location and its cause. Some of un-failed specimens were also dissected for the further analysis like as Fourier transform infrared spectroscopy and microscopy.