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Experimental Study on Deterioration Characteristics of Winding Insulation State in Double-Fed Wind Generator

To improve the operational reliability of wind turbines, it is of great significance to analyze or assess the deterioration characteristics of winding insulation state in double-fed wind generator. In this paper, the non-destructive characteristic parameters of the rotor winding insulation in a double-fed wind generator after eight years practical operation, including the insulation resistance, polarization index, dissipation factor and partial discharge inception voltage, were measured under different temperatures. The temperature spectrum of each insulation characteristic parameter from room to working temperatures was obtained. Additionally, a total of fifteen intact or undamaged coil sides from a rotor winding of failure wind generator were sampled for detecting the residual insulation state. From the temperature spectrums, the deterioration differences of the non-destructive characteristic parameters with the increase of the winding temperature was analyzed. Besides, the results measured from the sampled coils show that the average AC partial discharge inception voltage is about 1.8 kV, and the average residual breakdown voltage is 4.6~5.4 kV, which are greatly lower than that of 2.0~2.5 kV and 14~20 kV, respectively, for the newly manufactured wind generators. The more serious deterioration in the insulation state tends to occur at the bottom sides of coils, compared to those at top ones under the same operating conditions.