梯形电压波形参数对发电机定子绝缘局部放电特性的影响

Effect of Trapezoidal Voltage Waveform Parameter on Partial Discharge Characteristics of Generator Stator Insulation

局部放电检测是诊断高压电气设备绝缘系统缺陷和老化的有效手段之一,外加测量电压波形的改变有助于深入理解局部放电的物理过程。以对称梯形波电压为激励,基于电机定子绝缘在球形-平板非对称电极结构下开展局部放电试验,研究不同电压波形参数对局部放电特性的影响。结果表明:视在放电量主要集中在300~500 pC,与梯形波电压波形参数关系不大;最大放电量在外加电压的负半周整体上大于正半周,该差异主要是由放电电极的金属-介质非对称结构及空间电荷在介质表面的累积作用决定的;随着电压变化率dU/dt增大,平均放电量增加,相位偏移引起的时间延迟减小;随着水平电压持续时间增加,平均放电次数和平均放电量在整体上近似呈指数增长趋势。

Partial discharge(PD)measurement is an effective way to diagnose the defects and ageing of insulation system in high-voltage electrical equipment.The variation of applied voltage waveform can contribute to deeper understanding of discharge physical process.In this work,symmetrical trapezoidal-wave voltage was employed to investigate the effect of waveform parameter on PD characteristics,based on the PD activity produced in a spherical-plane asymmetric electrode structure on the stator insulation of electrical machines.The results show that apparent PD charge mainly concentrates around 300-500 pC,and it has little relation with the waveform parameter in the trapezoidal-wave voltage.Maximum PD charge in the negative half cycle of applied voltage is larger than that in the positive half cycle.This is mainly due to the metal-dielectric asymmetrical structure of test cell and space charges deposited on the dielectric surface.With the increase of voltage change ratio d U/dt,average PD charge increases,while time delay caused by the phase shift decreases.With the increase of constant-voltage period,both average PD number and average PD charge exhibit almost exponential increasing trend.