基于表面电荷动态分布测量的XLPE气隙直流局放内在影响因素及其作用机理研究

Partial discharge (PD), which takes place in a void embedded within high-voltage direct current (HVDC) cross-linked polyethylene (XLPE) cable, can cause the insulation failure, and poses a serious threat to the security operation of DC XLPE cable. Therefore, it’s necessary to fully understand the essence of DC void PD. However, PD has lots of influential factors and complex characters, and the action mechanism of internal factors with PD is confusing. This project will focus on PD taking place in a void embedded within XLPE under HVDC, and will deeply understand its mechanism by investigating the two internal action factors, i.e. surface charges and statistical time lag, which can affect the macroscopic properties and development process of PD. Firstly, the combination measurement system about surface charge and PD will be employed to obtain the surface charge dynamic distribution in a DC void PD sequence, by which the accumulation and decay mechanism of surface charge will be grasped. Secondly, based on the measurement of surface charge dynamic distribution, the calculation method of statistical time-lag will be proposed, so its statistical distribution and influential factors will be investigated. Based on the above research, the physical model about DC void PD will be established. The macroscopic characteristic parameters of PD will be obtained by experiments, while its microscopic development process will be clarified by simulation. Then, the effect of surface charges and statistical time lag on PD characters will be comparatively analyzed. Therefore, their action mechanism with PD will be revealed, and the theory about DC PD will be improved. This project will provide theoretical and technical support for assessing the impact of PD on the insulation performance of DC XLPE cable.

发生在高压直流交联聚乙烯(XLPE)电缆内部气隙缺陷的局部放电(PD)会造成绝缘失效，严重威胁着直流XLPE电缆的安全运行，因此有必要全面认识直流气隙PD本质。然而，PD的影响因素众多、特性复杂，且内在因素的作用机理尚不完全清楚。本项目以高压直流下的XLPE内部气隙PD为研究对象，从影响PD宏观特性与发展过程的表面电荷和统计时延两个内在因素来深入认识直流气隙PD机理，利用建立的表面电荷-PD联合测试系统，获取直流气隙PD序列中表面电荷的动态分布，掌握电荷积聚和消散机制，提出基于表面电荷动态分布测量的统计时延计算方法，研究统计时延的统计分布特点和影响因素，构建直流气隙PD物理模型，通过实验获取PD的宏观特征参数，利用仿真弄清其微观发展过程，对比分析表面电荷和统计时延对PD特性的影响规律，揭示其作用机理，完善现有直流PD理论，为准确评估PD对直流XLPE电缆绝缘性能的影响提供理论与技术支撑。

实验研究了直流气隙局部放电序列中表面电荷的动态分布特性，以及电压极性、幅值对表面电荷积聚和消散的影响规律，提取了放电前后表面电荷密度随时间的变化规律，并获取了不同电压幅值、极性以及电极结构下的直流局部放电特性。通过分析直流气隙局部放电中表面电荷积聚与消散对气隙电场的影响，建立了基于电荷流体方程的局部放电序列仿真模型，考虑了决定气隙局部放电行为的两个关键内在因素表面电荷和放电时延。模拟了不同电压极性和幅值下的局部放电特性，获取了放电序列中放电时间、视在放电量、放电电流波形等宏观参量，以及流注在气隙内的发展、流注到达气隙表面后的聚集过程，提取的直流局部放电统计参数与相同条件下的实验结果具有较好的一致性。通过实验和仿真的对比研究，进一步完善了直流局部放电机理，即：在局部放电序列中，表面电荷消散是后续放电得以产生的关键因素，表面电荷消散时间和放电时延共同构成了放电时间间隔，随着表面电荷消散速率的增加或者放电时延的减小，放电时间间隔减小，放电强度同时受放电时延和表面电荷消散速率影响。进一步研究了直流交联聚乙烯电缆的内半导电层破损、绝缘内部气隙和绝缘表面划伤三种绝缘缺陷在不同直流电压极性、幅值和电压持续时间下的局部放电特性，计算了三种缺陷在不同条件下的指纹参数，发现利用传统的指纹提取方法得到的指纹参数易受电压幅值、极性和老化时间影响，从而影响绝缘缺陷识别效果。分别采用了GA-BP算法和BRNN算法来优化局部放电指纹参数提取，排除了测试条件对指纹提取的影响，能够提高绝缘缺陷识别率。发表SCI检索论文9篇、EI检索论文3篇，包括1篇与IEEE Fellow George Chen教授合作的局部放电数值模拟的综述论文发表在IEEE TDEI，申请发明专利2项，编写英文专著章节1章，并入选中国电机工程学会青年人才托举工程。