【作者】 谷君；

【导师】 黄少锋； 郑涛；

【作者基本信息】 华北电力大学 ， 电力系统及其自动化， 2012， 博士

【摘要】 变压器是电力系统中重要的电气设备,在整个系统中起着能量传递的作用。差动保护作为变压器内部故障的主保护,在现场实际运行中将受到励磁涌流、TA饱和以及和应涌流等诸多因素的影响,进而发生误动。分析差动保护误动的原因并提出相应的防范措施,对提高变压器差动保护运行的可靠性具有重要的理论价值和现实意义。论文首先采用J-A理论进行TA建模研究,并利用该模型分析TA的饱和特性,作为后续章节的理论基础。在此基础上,针对电力系统实际运行中变压器差动保护的多种误动情况,分析了励磁涌流、TA饱和以及和应涌流等因素的影响,并提出相应的防范措施。论文的主要内容和成果如下：1.通过结合J-A (Jiles-Atherton)理论与TA特性方程,建立了考虑磁滞特性的TA动态分析模型。在此基础上,利用S-function、Masking Editor以及Symbolic Math Toolbox对其进行模块式开发。该模块不但具有计算准确、应用灵活、拓展性强等特点,同时可通过表达式输入的方式实现用户自定义模型的开发,并且支持多种形式的外部数据输入。应用该模型对TA的饱和特性进行分析,为本文后续章节提供理论基础。2.针对变压器区外故障切除后差动保护容易发生误动的情况,研究了TA饱和以及变压器Y侧电流相位补偿对差动保护的影响。根据保护的误动特点,提出利用多分区延时法以防止差动保护误动。该方法能够保证变压器在发生区外故障及区外故障切除后差动保护不误动,同时在经历变压器区内故障时迅速动作。3.针对变压器在发生转换性故障(区外转区内)时,差动保护不能及时开放的问题,根据TA饱和时在其一次电流过零点附近存在一小段线性传变区的特点,首先详细分析了变压器发生区内、外故障时差流的变化特征。在此基础上,利用数学形态学的方法构造奇异点与间断角检测算子,通过判断差流波形中是否存在间断识别变压器转换性故障。该方法能在TA饱和情况下正确识别变压器区内、外故障,并对于变压器发生转换性故障做出正确判断。4.研究内桥接线方式下的变压器差动保护误动实例,分别对励磁涌流、和应涌流以及TA饱和等因素的影响进行了详细分析,指出非周期分量引起的TA局部暂态饱和是造成内桥接线方式下变压器差动保护误动的主要原因。在此基础上提出了内桥接线方式下,基于时差法的防止变压器差动保护误动的新判据。该方法具有计算简单,快速可靠,识别特征明显等优点。5.针对变压器非同期空投时,未合闸相受已合闸相的影响可能发生超饱和,进而引起差动保护误动的问题,通过分析△绕组中环流的特点,提出了两种变压器非同期空投的识别方案。新方案不需要得到△绕组中的实际电流值,因此对分体式变压器与三相一体式变压器均有良好的效果。而后进一步提出了利用差流中二次谐波含量的变化趋势来防止变压器非同期空投时差动保护误动,以及变压器空投于内部故障时差动保护误闭锁。更多还原

【Abstract】 Transformer is one of the major electric apparatuses in power system. It plays an important role of power transfer in power system. Differential protection as the main protection of transformer will be influenced by many factors to mal-operate in actual operation, such as inrush current, CT saturation and sympathetic inrush current. Analyzing the reason of differential protection’s mal-operation and proposing the corresponding countermeasures has great theoretical value and important significance to improve the reliability of transformer differential protection. Firstly this paper uses Jiles-Atherton theory to simulate CT model, and analyzes the characteristics of CT saturation using this model as the theory basis of the following chapters. On this basis the paper makes an investigation on some mal-operation problems exist in transformer differential protection. Based on deep analysis of the mal-operation reason, new algorithms to solve these problems are provided. The major contributions of this dissertation are as follows:(1) Through combining the J-A(Jiles-Atherton) theory and CT characteristic equations, the CT dynamic analysis model considerating the hysteresis characteristic is established. After that a module development is completed using S-function、Masking Editor and Symbolic Math Toolbox. This module not only has many virtues such as accurate calculation、flexible application and great expansion, but also can realize the development of user-defined model through impression imput, and also support multiform external data imput. Applying this model, this chapter analyzes the saturation characteristics of CT, which provides the theory basis of the following chapters.(2) Aiming at the mal-operation of differential protection during the removal of transformer external faults, this chapter makes a deep analysis of the effect to differential protection of CT saturation and phase compensation. Based on the characteristic of mal-operation, multi-region time delay breaking method is creatively put forward to prevent the mal-operation of differential protection. This method can not only ensure differential protection not to mal-operate during external faults and the removal of external faults, but also can make the quick operation when internal faults occur.(3) According to that transformer differential protection could ont release in time when transferring fault (external fault to internal fault) occurs, this chapter firstly analyzes the characteristics of differential currents during internal and external fault, based on that CT’s secondary current has a little linear transmission area while the primary current crossed the zero point. On this basis, this dissertation proposed a method to recognize the transferring fault by checking the dead angle of differential current using oddity point and dead angle detection operators based on mathematic morphology. This method could correctly recognize the transformer internal and external fault under CT saturation, and could also make the right judgement of transformer transferring fault.(4) According to the mal-operation example of inner bridge connected transformer, this chapter respectively analyzes the impaction of inrush current, sympathetic inrush and CT saturation on the transformer differential protection. Study proves that the main reason of mal-operation is caused by CT partial transient saturation induced by non-periodic component. On this basis, a new algorithm based on time differential method to prevent differential protection mal-operation of inner bridge connected transformer is put forward. The new method has many virtues such as simple calculation、rapid、reliable、identification features are significant and so on.(5) During transformer’s non-synchronous closing, the phase already closed will induce the other phases to ultra saturation, and further will cause the mal-operation of transformer differential protection. According to the analysis of circulating current in wye-delta connected transformer, two new algorithms to identify transformer’s non-synchronous closing are put forward. The new algorithms need not get the actual currents in delta windings, therefore they have good results both for split type transformer and one body transformer. Following that this chapter puts forward a new method of detecting the second harmonic’s tendency in differential current. The new method could not only prevent the mal-operation during transformer’s non-synchronous closing, but also can prevent the error-lock during teansformer’s no-load closing on internal fault.更多还原