【作者】 吴麟琳；

【导师】 黄少锋；

【作者基本信息】 华北电力大学 ， 电力系统及其自动化， 2013， 博士

【摘要】 电力工业的高速发展在带来巨大经济效益的同时使电网日趋复杂,系统振荡发生的概率也大大增加。在系统发生振荡时,失步解列装置和继电保护装置的正确动作对于避免事故进一步扩大具有重要意义,振荡识别则是其核心技术之一。同时,随着电网建设的快速发展和土地资源的日益紧缺,双回线路日益增多,线路走廊也日趋紧密,因此有必要对双回线零序问题进行研究。本文以振荡过程中的电气量频率特征分析为基础,对基于频率特征的振荡识别原理进行了研究；同时以平行双回线对零序保护的影响分析为基础,对改进算法进行了研究。论文的主要内容和成果如下：研究了电力系统振荡过程中电流频率和电压频率的特征。对振荡中心和非振荡中心的电流频率和电压频率的表达式进行了推导,并根据其表达式对系统振荡过程中的频率特征进行了总结和分析。同时研究了两侧电动势幅值不等和系统内各元件阻抗角不等对频率特征的影响。研究表明当系统发生振荡时,只有振荡中心的电压频率等于电流频率；非振荡中心的电压频率在两侧电动势频率范围内随功角变化呈周期性变化。两侧电动势幅值是否相等或系统内各元件阻抗角是否相等均不对上述频率特征造成影响。提出了一种基于电气量频率差异的振荡识别原理。首先对系统振荡过程中电气量频率差异的特征进行了进一步的研究,引入了振荡因子的概念,用以表征某点电压频率和电流频率的比较情况。在此基础上,提出了基于电气量频率差异的振荡及振荡中心的识别原理。该原理可以判别系统是否发生振荡,并判断振荡中心是否在元件内部。同时该原理能够自适应于系统结构和运行方式的变化,且不受中间负荷变化的影响。提出了一种基于电压频率特征的振荡识别原理。首先对系统振荡过程中电压频率的特征进行了进一步的研究。对系统内任意点电压频率的导数进行推导,并对其特征进行了分析和总结,同时研究了两侧电动势幅值不等和系统内各元件阻抗角不等对电压频率导数特征的影响。以此为基础,提出了基于电压频率特征的振荡识别原理。根据其原理,该判据能够在振荡发生的首半个周期即判断出振荡中心是否位于元件内部；即使由于某种原因导致没能在振荡的首半个周期作出判别,该判据仍然可以在振荡的后半个周期再次作出判别。同时该原理也不受系统结构变化、运行方式变化及中间负荷变化的影响。研究了平行双回线对纵联零序方向保护的影响。采用互感线路的一般模型进行了故障计算,使研究具有通用性。以此为基础,分析了互感线路内部故障和外部故障时,其各端零序方向元件的动作行为,使零序方向元件受相邻线路电气联系强弱影响的现象更加直观化。同时根据一般模型的推导结果对互感线路的几种常见形式进行了进一步的研究。研究表明,故障线路纵联零序方向保护不受零序互感的影响,能够正确动作；对于与其存在互感的非故障线路而言,电气联系越紧密,零序方向元件误动的可能性越小；反之,误动可能性越大。因此在强磁弱电的情况下,可以采用纵联负序方向保护与纵联零序方向保护相结合的策略以防止零序方向保护的误动。提出了一种引入修正因子的反时限零序电流保护改进算法。首先分析了平行双回线对反时限零序电流保护的影响。对双回线内部接地故障时,零序电流的分布情况和保护元件的动作行为进行了分析。分析表明当故障点位置和系统零序参数满足一定条件时,非故障线路上的零序电流将大于故障线路上的零序电流,此时保护可能无法满足选择性的要求。为了解决这一问题,提出了引入修正因子的反时限零序电流保护改进算法,该算法可以同时提高反时限零序电流保护的选择性和速动性。更多还原

【Abstract】 The high-speed development of electric power industry, when bringing tremendous economic benefits, has made power grid become increasingly complicated and raised the probability of power system oscillation greatly. In case of system oscillation, the correct action of out-of-step splitting device and relay protection device has great significance for avoiding the further expansion of accidents, and oscillation identification is just one of the core technologies. Meanwhile, along with the fast development of power grid construction and the increasingly severe shortage of land resources, parallel transmission lines have increased day by day, and line corridor has become dense gradually, so it’s necessary to research zero-sequence problems of parallel transmission lines. Based on analyzing the frequency characteristics of electrical quantities during oscillation process, the criterion of oscillation identification based on frequency characteristics is proposed; and meanwhile, based on analyzing the influences of parallel transmission lines on zero-sequence protection, the improved algorithm is proposed. The main contents and achievements are as shown below:The characteristics of current frequency and voltage frequency during power system oscillation are studied. The expressions of current frequency and voltage frequency at oscillation center and non-oscillation center are dedeuced, and the frequency characteristics during system oscillation are analyzed. Meanwhile, the influences of unequal amplitudes of electromotive forces at both sides and of unequal impedance angles of each component inside the system on frequency characteristics are studied. The study has shown that, in case of system oscillation, only the voltage frequency at oscillation center is equal to the current frequency; while the voltage frequency at non-oscillation center changes cyclically along with the change of power angle within the frequency range of electromotive force at both sides. It has no influence on the above-mentioned frequency characteristics no matter whether the amplitude of electromotive force at both sides is equal, or whether the impedance angle of each component inside the system is equal.An oscillation identification criterion based on frequency difference of electrical quantities is proposed. Oscillation factor is defined to token the comparison of voltage frequency and current frequency. This criterion can judge whether the system oscillates, and whether the oscillation center is inside the component. Meanwhile, the criterion can self-adapt to the change of system structure and operating mode, without being affected by change of middle loads.An oscillation identification criterion based on the characteristics of voltage frequency change rate is proposed. The derivate of voltage frequency at any point inside the system is deduced, then its characteristics are summarized and analyzed. According to the theory, the criterion can judge whether the oscillation center is inside the component in the first half cycle of oscillation; even not, it can still make judgment in the second half cycle of oscillation. Meanwhile, the criterion is not affected by the change of system structure, operating mode, and middle load.To prevent the influences of parallel transmission lines on pilot zero sequence directional protection, improvement measures based on negative-sequence directional protection are proposed. The action of zero-sequence directional components at each end in case of internal and external faults of mutual inductance lines is studied. Study shows that, the protection of the fault line is not affected by zero-sequence mutual inductance, and can act correctly; for the non-fault line with mutual inductance, the closer the electric connection is, the smaller the probability of zero-sequence directional components misoperation will be. Therefore, in condition of strong magnetic and weak electric connection, the misoperation of pilot zero sequence directional protection can be prevented with the policy of combining negative-sequence directional protection and zero-sequence directional protection.To prevent the influences of parallel transmission lines on inverse-time zero-sequence current protection, an improved algorithm based on modifying factor is proposed. The distribution of zero-sequence current and the action of protection components in case of internal grounding fault are studied. The study shows that, when the position of fault point and the zero-sequence parameter of system meet certain conditions, the zero-sequence current of non-fault line will be greater than that of fault line, and here, the protection will probably not meet selective requirements. Meanwhile, the improved algorithm can raise the selectivity and the speed of inverse-time zero-sequence current protection simultaneously.更多还原