Partial discharges (PD) are small electrical discharges that occur within voids within the stator winding insulation system of a hydrogenerator. PD is harmful to the insulation: the repeated bombardment of electrons and ions on the void's surface gradually ruptures the chemical bonds of the insulation's organic materials and leads to electric treeing or electric tracking. In typical stator insulation systems that use mica tapes bonded by epoxy, deterioration of the insulation due to PD is usually slow (many years or decades). In hydrogenerator stator windings, PD is more a symptom of an aging process than a cause of deterioration [1].

中文翻译：

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水轮发电机定子绕组表面局部放电：原因、症状和补救措施

局部放电 (PD) 是在水轮发电机定子绕组绝缘系统内的空隙内发生的小放电。PD对绝缘有害：电子和离子在空隙表面的反复轰击逐渐破坏绝缘有机材料的化学键，导致电树或电痕。在使用由环氧树脂粘合的云母带的典型定子绝缘系统中，由于 PD 引起的绝缘劣化通常很慢（多年或数十年）。在水轮发电机定子绕组中，局部放电更多是老化过程的征兆，而不是退化的原因 [1]。