Evaluation Method of Stator Insulation for Direct-drive Wind Turbine Generator Based on Accelerated Multi-factor Aging

In this paper, a new procedure for the accelerated multi-factor aging test was firstly established for evaluating the insulation system of a wind turbine generator, in which, especially, a stepwise electric stress from 2 to 3 and finally up to 4kV (rms) have been applied based on the relevant criteria. A few test specimens for modeling the stator insulation system of megawatt class wind turbine generator were prepared. The multi-factors of the power frequency electric stress combined with humidity, temperature change and vibration, in turn, were applied to the specimens for the periodical aging tests, and at least 22 periods of aging tests have been conducted in the laboratory. Some of non-destructive characteristic parameters, such as dissipation factors, insulation resistances, polarization indexes, and partial discharge inception voltage have been measured. In addition, the comparisons of the micro-structures of insulating material between the aged and un-aged specimens were finally observed by means of some microscopic analyses also. The testing results show that, the combined test condition will become a vital aging factor only at a higher electric stress, which resulted in a sharp decline in insulation resistance and a rapidly increasing dissipation factor. Finally, a primordial evaluation method of insulation system for direct-drive wind turbine generator based on this accelerated multi-factor aging research has been proposed.