直流偏磁对变压器差动保护的影响及抑制

发布时间：2018-01-08 16:37

本文关键词：直流偏磁对变压器差动保护的影响及抑制　出处：《东北电力大学》2012年硕士论文　论文类型：学位论文

【摘要】：直流偏磁是指在变压器励磁电流中出现了直流分量的现象,是变压器的一种非正常运行状态。当直流量进入变压器之后，会使变压器铁心半周饱和,在励磁电流中产生大量谐波,导致变压器损耗增加、温升，从而引发变压器局部过热、噪声增大、振动加剧，系统电压下降，继电保护误动作等一系列现象，严重威胁电网安全运行。在直流偏磁问题的研究上，国内外学者主要侧重于直流量大小的计算及抑制措施改进方面，对变压器保护影响方面的研究还比较欠缺。因此本文首先阐述了直流偏磁产生的机理，同时对不同直流偏磁条件下，变压器磁链、励磁电流和谐波的变化情况进行了理论分析，并研究了谐波的变化情况给变压器差动保护带来的影响。基于以上的理论研究，本文利用PSCAD/EMTDC搭建了具体的仿真模型，分别仿真了不同的直流偏磁情况下，变压器正常运行、励磁涌流以及各种内部故障时励磁电流和谐波的变化情况，并利用Matlab对PSCAD中导出的数据进行了编程处理，得出了变压器保护的动作情况，，对比分析可知直流偏磁会使变压器差动保护拒动。目前，解决变压器差动保护拒动问题的途径主要有两种：一是减小变压器中性点直流量；二是在原来保护的基础上改进保护算法。国内外研究表明，减小直流量的三种措施在经济性和安全性方面各有优缺点，在实际电网中投入运行的很少。因此，本文采用途径二解决由直流偏磁引起的变压器拒动问题。通过大量仿真研究发现直流偏磁下发生内部故障并且差动保护拒动时，变压器中的差流有其独特的谐波特性，所以本文据此提出了一种新的保护算法。通过验证分析，此方法简单、可靠、易行，并且不会对电网造成额外的危害。
[Abstract]:DC bias is the phenomenon of DC component in the excitation current of transformer. It is a kind of abnormal operation state of transformer. When the direct current enters the transformer, it will make the transformer core half cycle saturated. A large number of harmonics are produced in the excitation current, which leads to the increase of transformer loss and temperature rise, which leads to a series of phenomena, such as transformer local overheating, increased noise, intensified vibration, system voltage drop, relay protection misoperation and so on. It is a serious threat to the safe operation of power grid. In the research of DC bias, domestic and foreign scholars mainly focus on the calculation of the direct flow and the improvement of the suppression measures. The research on the influence of transformer protection is still lacking. Therefore, this paper first describes the mechanism of DC bias magnetic field, and at the same time, the transformer flux chain under different DC bias conditions. The variation of excitation current and harmonic is analyzed theoretically, and the influence of harmonic variation on transformer differential protection is studied. Based on the above theoretical research, this paper uses PSCAD/EMTDC to build a specific simulation model, respectively, under different DC bias conditions, the normal operation of the transformer. The variation of excitation current and harmonics in inrush current and various internal faults is analyzed. The data derived from PSCAD are programmed by Matlab, and the operation of transformer protection is obtained. The contrast analysis shows that DC bias will cause transformer differential protection to refuse operation. At present, there are two main ways to solve the problem of transformer differential protection rejection: one is to reduce the direct flow of transformer neutral point; The other is to improve the protection algorithm on the basis of the original protection. Domestic and foreign studies show that the three measures to reduce the direct current have their own advantages and disadvantages in economic and security aspects, and few of them are put into operation in the actual power grid. In this paper, path two is adopted to solve the problem of transformer failure caused by DC bias. Through a large number of simulation studies, it is found that the internal fault occurs under DC bias and the differential protection fails to operate. The differential current in transformer has its unique harmonic characteristics, so a new protection algorithm is proposed in this paper. It is proved that this method is simple, reliable and easy to carry out, and will not cause additional harm to the power network.
【学位授予单位】：东北电力大学
【学位级别】：硕士
【学位授予年份】：2012
【分类号】：TM772

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