【作者】 王媛媛；

【导师】 简金宝； 曾祥君；

【作者基本信息】 广西大学 ， 电力系统及其自动化， 2012， 博士

【摘要】 非有效接地电网馈线接地保护是我国在建、改建的配电系统亟待解决的重要课题。但由于故障残流小、故障电弧及干扰影响等原因,现有方法在实际运行中选线正确率很低。Powerformer是一种高压发电机,其中性点广泛采用经高电阻接地方式或经消弧线圈接地方式,也属于非有效接地电网。Powerformer的内部故障机理及选择性定子单相接地保护研究,是目前鲜有报道的保护领域最新研究方向,需要深入研究。论文共分为七章,第一章为绪论,第二章至第六章为主要研究工作,第七章对全文进行了总结。本文主要研究成果如下：(1)馈线接地保护是非有效接地电网中长期存在的难题。为深入挖掘故障信息的本质特征和内在规律,对多源故障信息进行有机综合处理,论文第二章介绍了样本相似性度量和类间距离的计算方法,给出定量判定聚类有效性的方法,寻找出适用于馈线接地保护的最佳系统聚类算法；提出了系统聚类故障检测的模型与方法,根据零序导纳法、负序电流法、零序电流法、接地故障电阻法、小波分析法、零序能量函数法等多源故障信息的相似性程度,即空间距离的远近进行保护判断。仿真分析表明：该选线方法不受系统运行方式变化的影响,能满足配电自动化的要求,有望提高配电网故障选线的精度和鲁棒性。(2)非有效接地电网馈线接地保护中,各种故障保护方法所获取的信息或多或少地受到系统参数变化、干扰等因素的影响,具有一定的模糊性。为建立样本对于类别的模糊描述,更客观地反映样本数据的模糊特征,论文第三章提出了一种基于模糊聚类分析的馈线接地保护方法。首先,采用模糊C均值聚类分析方法,采用不同属性的故障特征量,以4种基于稳态的保护方法和3种基于暂态的保护方法提取出的多源信息为指标,将历史数据分成故障类和非故障类；然后,根据各聚类中心与待测样本的空间相对距离识别出待测样本的故障类别,从而实现感知到认知的过程,完成保护判断。仿真分析验证了该方法的有效性和可行性,同时表明干扰、系统运行方式和过渡电阻等因素对该方案影响很小。(3)为提高非有效接地电网馈线保护方法的鲁棒性和精度,论文第四章应用统计学理论并结合工程实际,借助判别分析方法将稳态故障信息和暂态故障信息进行融合处理,选取5个故障特征量作为故障选线的判别因子,建立距离判别分析模型,并利用回代估计法对距离判别分析模型进行检验。通过配电网单一保护单元内部不同选线方法在不同历史时段所呈现出的特性不同,构建面向单一保护单元的选线方法,实现感知到认知的过程,完成选线判断。研究结果表明,经过训练后的判别分析模型误判率较低。利用该模型对待测样本数据进行测试,测试结果与实际情况吻合,验证了该接地故障选线方法的高效性和实用性。(4)高压发电机在系统中处于重要地位,其定子绕组单相接地故障保护需可靠灵敏以及具有100%的保护范围,对于并列运行的多台高压发电机,需具备选择性。论文第五章分析了定子单相接地故障前后Powerformer机端零序电流基波分量和三次谐波故障分量的变化特征。通过比较各高压发电机零序电流的大小和能量判断单相接地点是否在本发电机定子绕组内部。给出了不同接地点和不同过渡电阻情况下的仿真结果,仿真分析结果表明：该保护方案可实现100%定子接地保护,能可靠地识别出发电机内部、外部的定子接地故障,判断故障发电机。该方案构成原理较简单,具有鲁棒性强,精度高等特点。(5)对于一个具有若干台机组的大型电厂,所用发电机组会通过厂内的公共母线进行功率汇集,再向系统统一供电。针对并列运行发电机组的选择性定子绕组单相接地保护问题,论文第六章基于高压发电机内部故障仿真模型,分析了高压发电机发生定子绕组单相接地故障时的电气特性,利用故障发电机与非故障发电机零序功率方向不同的特点来实现有选择性的保护。利用零序功率的基波分量和三次谐波故障分量共同判断单相接地点是否在本发电机定子绕组内部,实现100%定子接地保护。给出三种运行状态(正常运行、外部故障、内部故障)的仿真结果。理论分析和仿真结果表明,该保护原理不仅能有效检测接地故障,还可较好地区分故障发电机与非故障发电机。更多还原

【Abstract】 Neutral Ineffectively Earthed Power Systems (NIEPS) include neutral unearthed system, neutral earthed with high resistance system and neutral resonance earthed system. Single-phase-grounding faults potentially cause cables bombing or phase to phase faults in NIEPS, and the safety and power quality of the distribution system will be affected. Traditional single-phase grounding faults protections have low precision and reliability in NIEPS, because of the small fault current, fault arc, harmonics influence and the protection principle limitation. A new type of high-voltage generator which offers a direct connection to the power network without the need for a step-up transformer is called Powerfonner. Under most conditions, Powerformers are with neutral unearthed, and they belong to NIEPS. Since the Powerfonner was invented in1998and has not been researched well, it is very necessary to study the machanics of internal or external fault in Powerfonner, and the stator single phase-to-ground fault protection. The thesis’ aims are to find the shortages of the traditional grounding faults protection methods, and to develop some novel protections for NIEPS in detecting and isolating grounding faults.This thesis contains seven chapters. The introduction of Neutral Ineffectively Earthed Power Systems is introduced in the first part of this thesis. Chapter two to six are devoted to the main works. The details of this paper are as follows:(1) Earth fault feeder detection is a long-standing problem in Neutral Ineffectively Earthed Power Systems. Hierarchical clustering analysis is an important technique in studying for multi-sources information integrating and processing, and is introduced and applied in feeder grounding fault protection in chapter two. A method that can quantitative discriminate the validity of the hierarchical clustering is proposed. Four steady parameters based protection and three transient signal based protection are selected as the fault characters. The models and methods of hierarchical clustering for information fusion technique in feeder grounding fault protection are presented. The scheme has been verified by EMTP simulation, and results show that the scheme has high sensitivity and robustness.(2) Hierarchical clustering analysis is crisp partition, which has opposite law, meaning A and not-A. However, traditional ground fault protection has fuzzy characteristics because of the influence by variation parameters and disturbing signal. In order to describe the fuzzy characteristics, a novel principle for feeder grounding fault protection based on fuzzy clustering analysis is presented in the third chapter. First, the historical data is divided into two groups by fuzzy clustering analysis. The space relative distance among detected patterns and two cluster centers is then calculated to discriminate the fault feeder. The scheme has been verified by EMTP simulation. The results show that the effect of the disturbing signal can be reduced, inherent limitation of the single protection scheme can be eliminated and the precision and robustness of fault detection can be improved.(3) In order to improve the precision and reliability of traditional earth fault feeder detection schemes for Neutral Ineffectively Earthed Power Systems, on the basis of the Mahal distance discriminant theory and in combination with the project practice, a distance discriminant analysis model of earth fault feeder detection scheme is established in chapter four, in which five parameters are selected as the discrimination factor. The back substitution method is introduced to verify the stability of the distance discriminant analysis model and the ratio of mistake-discrimination was equal to zero after the distance discriminant analysis model was trained. By means of the model, other four groups of measured data are tested as testing sample, and the result are consistent with the measured data. The simulation results show that the distance discriminant analysis model has a higher accuracy and low mis-discrimination ratio.(4) In order to resolve the selective protection for Powerformer with more than one generator directly connecting a bus, the characteristics of the stator winding phase-to-ground zero-sequence current (zero-sequence fundamental component and third-harmonic fault component) are analyzed in chapter five. Through comparing the magnitude of zero-sequence currents and fault point energy dissipation, the stator grounding faults can be detected occurred in generator stator winding or not. Simulation results show that the fundamental component and the third-harmonic fault component of zero-sequence current are combined to realize100%coverage of fault detection for the stator windings of Powerformer. What’s more, the protection can distinguish the single-phase earthed fault occurred in stator winding or outside of generator, and can detect stator ground faults in which generator with high sensitivity and selectivity.(5) When a stator single phase-to-ground fault occurs in a powerformer, every generator that is connected in parallel’with the faulty powerfonner has the same voltage. Traditional protection schemes using zero sequence voltage and third-harmonic voltage signals cannot detect which powerformer is faulted. In order to solve this problem for Powerformer protection, a novel stator single phase-to-ground fault protection based on the direction of zero-sequence power is proposed in chapter six. Simulation results have shown that, under different fault conditions, the new scheme can distinguish reliably internal faults from external faults, and can detect stator single phase-to-ground fault occurred in which powerformer with100%of the winding.更多还原