【作者】 梁睿；

【导师】 王崇林；

【作者基本信息】 中国矿业大学 ， 电力电子与电力传动， 2010， 博士

【摘要】 配电网发生的故障大部分都是单相接地故障,小电流接地系统的故障选线准确性受很多因素影响,因此小电流接地系统的单相接地故障选线问题一直是继电保护领域研究的一个难点。针对不同中性点接地方式配电网的单相接地故障,本文详细分析了零序电压变化规律及故障暂态零序电流和稳态零序电流的变化规律,建立了电弧型接地故障模型并进行了仿真,将PT断线故障、系统断线故障及铁磁谐振故障引起的零序电压升高与单相接地故障引起的零序电压升高进行比较,得出正确判断单相接地故障发生的方法。本文提出了消除不平衡电流的有功分量选线方法、基于比较暂态零序电流小波变换模极大值的平方值的选线方法和基于故障零序电流灰色关联分析的小电流接地选线方法三种选线新方法。本文采用一种改进型的付氏算法来进行各物理量有效值的准确计算,用以消除干扰信号的影响;接地故障的暂态特征蕴含了丰富的故障信息,小波变换能准确地从暂态故障信号中提取出有用的故障信息,本文提出了一种基于比较暂态零序电流小波变换模极大值的平方值的选线判据,扩大了故障支路和非故障支路故障特征的差异;基于暂态零序电流灰色关联分析的小电流接地选线方法是利用健全线路零序电流和故障线路零序电流的关联程度的强弱来构造故障选线判据的自适应方法。研究表明,单一的选线方法在某些情况下效果明显,但不能适用于所有的故障情形。只有采用多种方法对故障产生的各种信息进行全面的分析和综合运用,才能适应更多的故障情形,提高故障选线的准确性和有效范围。基于多种选线方法的综合选线是提高故障选线范围和准确性的一种很好的思路,也是目前故障选线领域的一个研究前沿。本文分析了对不同故障的类型进行识别的必要性,综合选线法是利用加权关系法对基于稳态量和暂态量的多种方法进行组合来实现的,而不同单相接地故障的特征有所不同,如电弧型接地和瞬间性接地暂态特征比较丰富,而电阻性接地稳态分量丰富,因此有必要针对不同的故障特征合理地选用相应方法并确定方法权值,以期达到最佳选线效果。本文利用多重分形理论对稳定接地和不稳定接地故障的零序电压进行计算,得出多重分形特征和故障类型的关系。依据不同故障的零序电压多重分形特征可以判断出故障趋向于稳定接地和不稳定接地的程度,从而为利用加权系数法的多信息融合选线中基于稳态量和暂态量的各方法的加权系数的制定提供了依据。模糊理论是处理复杂不确定问题的方法,论文分析了运用模糊理论实现多判据信息融合选线的方法,同时指出传统模糊理论不能完整表达故障全部信息的不足。直觉模糊集理论是传统模糊集理论的推广,能够更全面地利用故障信息,更好地实现多判据融合选线。本文提出了基于直觉模糊决策方法的小电流接地故障选线方法,合理地解决了故障选线问题中线路故障特征隶属度、非隶属度的确定问题,并根据故障零序电压多重分形谱计算不同故障特征的权重,解决了以往无法根据故障特征合理分配加权系数的问题。基于直觉模糊信息集成理论的故障综合选线方法根据故障特征趋向于暂态和稳态的程度来合理确定暂态量选线方法和稳态量选线方法的权重,进而对故障特征信息进行融合,实现综合选线,全面利用了各种故障信息,提高了选线准确性。论文中基于直觉模糊理论的综合选线方法利用上述三种单一选线方法分别确定故障稳态特征、暂态特征和灰色关联特征的隶属度,用零序电压多重分形谱计算得到故障特征的权值进行信息融合,实现综合选线。大量仿真和模拟试验的结果证实了直觉模糊综合选线方法的可靠性和优越性。更多还原

【Abstract】 Distribution faults are mostly single-phase earth faults, the accuracy of fault line selection in small current neutral grounding system is affected by many factors, so fault line selection for single-phase earth faults in small current neutral grounding system has been a difficult point in the field of relay protection.Detailed analysis on the variation of zero sequence voltage, transient zero sequence current and steady state zero sequence current of distribution single-phase earth fault in different neutral grounding modes was made in this dissertation. The model of arc grounding fault was built and simulation was carried out, the increases of zero sequence voltage caused by PT breaking fault, line breaking fault and ferroresonance fault were compared with the zero sequence voltage increase caused by single-phase earth fault, the method to correctly judge single-phase earth fault was got.Three new methods for fault line selection are proposed in this dissertation, they are active power method to eliminate unbalanced current, fault line selection method based on the comparison of the square value of wavelet transform modulus maxima of transient fault zero sequence current and fault line selection method based on grey relational analysis of zero sequence current. This dissertation proposed an improved type of Fourier algorithm to calculate the effective value of physical quantities accurately, and it eliminated the effect of interference signals. Transient characteristics of the grounding fault contain abundant fault informations, wavelet transform can extract useful fault information from the transient fault signals accurately. A new criterion of fault line selection based on the comparison of the square value of wavelet transform modulus maxima of transient fault zero sequence current was proposed in this dissertation, and it enlarged the fault differences of fault branch and non-fault branches. Fault line selection method based on grey relational analysis of zero sequence current uses the zero sequence current correlation degree of fault branch and non-fault branches to construct an adaptive fault line selection criterion. Research shows that single fault line selection method has obvious effect in some conditions, but isn’t suitable for all conditions. It can suit more fault conditions when several methods were used to make comprehensive analysis on the various information produced by fault and use them comprehensively, the accuracy and effective range of fault line selection method also can be raised. Comprehensive method for fault line selection based on several methods is a good way to raise the accuracy and effective range of fault line selection, and it is a research frontier of the fault line selection field.Necessity of the identification of different types of faults were analyzed in this dissertation, comprehensive method for fault line selection was realized by the combination of fault line selection methods based on steady component and transient component using the weighted coefficient method. Different single-phase earth faults have different characteristics, transient component is relatively rich under the conditions of arc grounding fault and instantaneous grounding fault, and the steady component is relatively rich under the condition of resistance grounding fault. So, it is necessary to select weights of different methods reasonably based on different fault characteristics in order to achieve the best fault line selection results. Multi-fractal theory is used to calculate zero sequence voltage of stable and unstable grounding fault,and the relationship between multi-fractal spectrum range and fault type was got. According to different fault zero sequence voltage multi-fractal characteristics, the degree of the fault tending to stable and unstable grounding fault can be determined, thus it provides a basis for determining the weighted coefficient of fault line selection methods based on steady component and transient component used in information fusion method. Fuzzy theory is a method to deal with complex uncertainty problems, this dissertation made an analysis on multi criteria information fusion fault line selection method based on fuzzy theory, and pointed out insufficient point that the traditional fuzzy theory can not completely express all the fault information. Intuitionistic fuzzy sets is the extension of the traditional fuzzy sets, it can use fault information more completely, and achieve multi criteria information fusion fault line selection better.A comprehensive method for fault line selection based on intuitionistic fuzzy information integration theory was proposed in this dissertation, and the problems of determining membership degree and non-membership degree of fault characteristics for fault line selection was rationally solved. Weights of different fault characteristics were calculated according to the multi-fractal spectrum of zero sequence voltage, it solved the problem that previous weighted coefficient method can’t select weights of different methods reasonably based on different fault characteristics. The comprehensive method based on intuitionistic fuzzy theory determines the weighted coefficients of fault line selection methods based on steady component and transient component reasonably according to the degree of the fault tending to stable and unstable grounding fault, information fusion of fault characteristics was made. It uses the fault information completely and raises the accuracy of fault line selection.The comprehensive method for fault line selection based on intuitionistic fuzzy theory proposed in this dissertation make use of the aforesaid three kinds of single fault line selection methods to determine the membership degree of fault steady characteristics, transient characteristics and grey correlation characteristics separately, it uses zero sequence voltage multi-fractal spectrum to calculate weights of the three methods in order to make information fusion, and finally achieve comprehensive fault line selection. A lot of experiment and simulation test results confirmed the reliability and superiority of intuitionistic fuzzy comprehensive method for fault line selection.更多还原