【作者】 鲁文军；

【导师】 刘沛； 林湘宁；

【作者基本信息】 华中科技大学 ， 电力系统及其自动化， 2007， 博士

【摘要】 自适应保护的基本思想是使保护尽可能地适应电力系统的各种变化,改善保护性能,即能够适应电力系统各种运行方式和复杂故障类型,有效地处理故障信息,从而获得更可靠的保护。本文介绍了自适应保护的基本概念、分类方法、研究的意义及在电力系统中的应用等问题。并详细地讨论了自适应技术在故障选相、突变量距离保护、自动重合闸等中的应用。现代数字信号处理技术是分析电力系统故障信息的有力工具,已经在电力系统各个领域取得了广泛应用,同时也为自适应技术在继电保护中的应用提供了强有力的手段。数学形态学(MM)是继小波分析后又一个新型的数字信号处理工具。是一门建立在集论基础之上的学科,它是几何形态分析和描述的有力工具,被广泛应用于信号、图像分析和处理等工程领域。不同于很多其它的信号处理技术,数学形态学面向的是信号的时域波形而不是从频域或时频域入手。作为一种非线性变换,形态学滤波器通过改变信号或图像的一些局部几何特征,便可以提取有用的信息做特征分析和描述。形态变换主要为比较运算及少量的加减运算,可以认为,与传统的数字滤波算法相比,形态学滤波单元仅占用很少的保护处理时间,它在继电保护乃至电力系统其它领域具有良好的应用前景。针对传统电流突变量和电压突变量选相元件不能同时满足强弱电源系统侧保护要求的缺点,提出一种新的突变量选相原理。该选相元件在电压突变量基础上引入单相电流突变量进行极化,不但能自动适应系统运行方式的变化,尤其在系统正负序阻抗不等导致传统突变量选相元件失效的场合,更能体现出其优越性。值得指出的是,该选相元件对单相短路故障和相间短路(接地)判断均有很高的灵敏度。EMTDC仿真结果表明,即使在正负序严重不对称的场合,该元件也具有很好的选择性。当系统参数大范围变化时,该选相判据也能实现正确选相,比传统突变量选相方案具有更高的可靠性。针对传统突变量距离保护在两侧系统电势相位差较大时发生外部短路等情况有可能误动的缺点,首先分析了传统解决办法的局限性,提出了两种借助同步相量测量技术提供的信息,根据系统实时参数自适应调整保护动作门槛的新算法。方法一通过理论证明,确定了原有判据发生误动的边界条件,在此基础上,提出了以α=90°为边界切换动作门槛的新判据,方法二则通过精确计算,确定保护不误动的动作门槛,从而在故障时通过计算实时调整保护的定值。两种新的判据对于保护区整定在本线路内的突变量距离保护,其动作可靠性和灵敏度都得到了提高。ATP仿真结果验证了判据的有效性,本论文的工作也为同步相量测量技术在继电保护中的应用途径提供了一种新的思路。提出了一种基于电流行波极性同时适用于线路方向保护和母线保护的综合保护(简称IDR)新方案。其中的线路保护功能只是IDR的一个跳闸输出,可看作为虚拟方向保护(简称VDR)。在获取连接在同一母线上的各条输电线路的暂态电流信号的基础上,采用数学形态学分析其极性的能量以确定故障方向。当采集的所有线路电流的极性相同时,可以判断为母线故障。否则,可以通过其中一条线路的VDR判断为该线路的正向故障。另外,这种新的方向保护可以和传统的方向保护、距离保护、母线电流差动保护构成主保护多重配置方案。目前,大多数自适应重合闸方案中,均采用故障相的高频能量进行瞬时性和永久性故障的区分。针对单窗能量函数难以用单一阀值区分故障以及传统滤波器难以有效抑制高频噪声的缺陷,提出了两种双窗函数暂态能量比的判据。如果滤波器效果良好,该判据在信号平稳段的输出接近1,在信号奇异时刻附近,能量比明显增强,便于整定。为了更有效提取高频能量,采用论文提出的两种新的数学形态学算子GMMG和COOCG,对高频能量信号进行滤波,EMTP仿真研究表明,由采用两种算法构成的自适应重合闸方案都能提高判别的可靠性,具有实用价值。论文最后对本文的全部理论和应用研究成果进行了系统的总结,指出了自适应保护技术及数学形态学算法本身在电力系统继电保护的应用中有待进一步研究的问题。更多还原

【Abstract】 The self-adaptive protection aims at achieving the best performance in the event of changes of power system operation modes. This paper introduces the basic concept of adaptive protection, as well as the issues of classification, the meanings of research and the applications in power systems. Besides, the applications of adaptive technique in the field of phase selector, superimposed distance protection, as well as auto-reclosure are dissucssed in details.Mordern signal processing technique, as a powerful tool to analyze the fault information of the power systems, has been widely applied in various fields. And it also provides a powerful means for self-adptive technology to be used in protective relaying. Mathematical morphology (MM) is one of the latest techniques in advanced signal processing fields. MM is developed from set theory and integral geometry, and is widely used in geometrical analysis and description. It is concerned with the shape of a waveform in time domain rather than frequency. Morphological filters are nonlinear signal transformation that locally modifies geometrical features of signals and image objects. Morphological calculation needs only the comparison and addition operations without multiplication, the computational complexity, therefore, is much smaller than conventional digital filter algorithms. Thus, it has the excellent foreground in protection and even the other areas of power system.A novel superimposed phase selector aiming at improving the performance of phase selector in the event of a wide range change of power system operation mode is presented in this dissertation. In this new scheme, the fault component of phase-phase voltage difference is polarized with the fault component of the third phase current. With this arrangement, this element not only adapts to various operating modes of power systems, but is superior to the traditional superimposed phase selectors. For instance, the superimposed phase-phase current difference based phase selector or the superimposed phase-phase voltage difference based phase selector, in terms of selectivity and sensitivity. The advantages of this phase selector can be highlighted especially in the case of the positive-sequence impedance not being equal to the negative-sequence impedance. In addition, this phase selector can reliably identify the single-phase-earth fault and the phase-to-phase fault. The results of EMTDC simulation tests show that the outstanding phase selection performance can be achieved even when the negative-sequence system impedance is extremely unequal to the positive-sequence system impedance. Besides, this phase selector has higher reliability compared to the traditional superimposed based schemes.Aiming at the defects of the conventional superimposed distance relay, for instance, the mal-operation resulting from an external earth fault occurring while the transmission system operates at large power angle, two novel self-adaptive superimposed distance protection scheme is proposed. Utilizing information of the wide area phasor measurement units (PMU), the two schemes can adjust the operation threshold dynamically, depending on the real-time parameter measurement of two equivalent power systems. In the first scheme, the boundary conditions of mal-operation of previous criteria are deduced in theory. Then, a new criterion to swithch the threshold value depending onα=90°is put forward. In the second scheme, the accurate threshold value for operation is caculated in theory, is used to adjust the setting in real time. By virtue of this arrangement, the reliability and sensitivity of the superimposed distance protection of Zone I are improved. The effectiveness of the new criterion is verified with the results of ATP simulations. Besides, the work of this paper also provides a new path to introduce the PMU technique into the protective relaying.A new integrated directional relaying principle for transmission line and busbar is presented. This novel directional relay, which integrates the protective functionality of line directional protection and busbar protection, is implemented with the polarity comparison of the current travelling waves. The function of line directional protection of the integrated directional relay (IDR), which is actually the protective decision of IDR, is defined as the virtual directional protection (VDP). Using morphological gradient to characterize the initial current travelling wave into spike signal the direction of a fault can be determined by the polarity comparison of the formulated spike signals. A busbar fault can be detected if all the compared spike signals have the same polarities. Otherwise, a forward fault will be identified by the VDP of one of the transmission lines connected to this busbar. In addition, the integrated directional relay is used to consist of the duplicated main protection scheme combined with the classical directional protection, classical distance protection and differential protection of busbar. By virtue of the individual protection principles and the measurements, the proposed duplicated protection scheme is promising to obtain higher reliability compared with the conventional schemes.At present, most self-adaptive auto-reclosure schemes are dependent on the high-frequence power energy information sampled from the transmission lines to distinguish between the instant faults and the permanent fault. Aiming at the defects of the conventional schemes, for instance, the single-window transient energy ratio based scheme is difficult to identify the fault using the single threshold value and the high-frequency noise can not effectively decrease by the conventional filter, two individual criteria of dual-window transient energy ratio (ER) are proposed. This ER approaches to 1 during the steady state whereas it increases greatly around the time instants at which the signal appears the singularity. Therefore, the setting of the criterion is easy. To effectively extract the high-frequency energy of the modal information, two different morphological algorithms (GMMG and COOCG) are put forward. EMTP based simulation results show that the GMMG and COOCG based auto-reclosure scheme improves the reliability of discrimination and is promising to be used in the real power systems.All the theoretical innovations and application studies are summarized in Chapter 8, where a few prospective issues about self-adaptive technology and MM worthy studying are also proposed.更多还原