【作者】 孙向飞；

【导师】 于继来； 束洪春；

【作者基本信息】 哈尔滨工业大学 ， 电力系统及其自动化， 2008， 博士

【摘要】 行波保护原理上不受过渡电阻、故障位置等影响,并具有超高速动作特性,是一种理想的保护原理。虽然已经提出了许多具体的行波保护方法,但它们主要针对正常运行线路中发生故障的情况,没有考虑断路器合闸,特别是不同期合闸对保护正确动作的影响。为完善行波保护、推进其实用化,有必要对断路器合闸产生的行波特征进行深入分析,并在此基础上提出新的行波合闸保护方法。近年来,国内外出现了多起空投变压器引起相邻运行变压器产生和应涌流导致差动保护误动的报道。目前,此方面的研究主要集中在和应涌流的产生及其变化特点,而分析问题所考虑的因素与实际还有一定差距,对和应涌流引起差动保护误动的内在原因认识也还不够深入。这就迫切需要进一步系统深入地研究并掌握和应涌流变化的新规律,从而由此提出完善变压器差动保护的新措施。本文工作主要从上述两方面展开。一是通过输电线路合闸行波特征的分析,提出考虑不同期合闸的行波保护新方法;二是通过变压器和应涌流变化规律及引起差动保护误动内在原因的探究,提出正确识别和应涌流、降低差动保护误动率的新方法。为能正确快速得出输电线路不同故障位置、故障类型和过渡电阻情况下合闸时正反向初始行波的极性与幅值关系,本文提出了计算输电线路不同期合闸时故障点各模量行波反射系数及相互透射系数的方法。由此方法,可分析出:当线路中部故障时,正反向初始电流行波极性相同,这与输电线路正常运行发生故障时的情况相同;当线路末端故障时,正反向初始电流行波极性关系受故障类型、过渡电阻及故障相是否先合等因素的影响,当过渡电阻较大且先合故障相时,或存在严重故障且故障相不是先合相时,将会出现正反向初始电流行波极性相反的情况,这与线路无故障时合闸的行波极性关系相同,导致现有方法出现误判。为考虑实际三相断路器不同期合闸的影响,并使保护能够在线路中部或末端故障时均能正确动作,本文提出了一种新的行波合闸保护方法,方法基于:当线路合闸时,若线路无故障,则电流行波在线路末端的反射系数为-1;若有故障,故障点的反射系数不是-1。仿真结果表明新的保护方法在各种情况下都能正确动作。变压器和应涌流的产生与变化受许多因素的影响,而现有研究对两台不同容量变压器相互作用及变压器带负荷情况分析不够,影响了对变压器和应涌流整体规律的掌握程度。针对此现状,论文比较研究了串并联和应涌流的产生过程及特点,分析了多种因素,特别是运行变压器负荷对和应涌流特征的影响,揭示了不同条件下变压器和应涌流变化的新规律,为认清和应涌流造成变压器差动保护误动的内在原因提供了基础。为找寻和应涌流引起变压器差动保护误动的真正原因,论文分析了和应涌流与励磁涌流的二次谐波含量关系、CT暂态饱和对和应涌流二次谐波含量与间断角的影响、CT星-三角变换对差动电流二次谐波含量的影响等。分析结果表明:变压器和应涌流与励磁涌流的二次谐波含量及间断角特征相近,但前者相对于后者,衰减缓慢,容易造成CT饱和,导致差动保护不能正确测量到和应涌流,可能引起差动保护的误动作。为进一步明确和应涌流引起变压器差动保护误动的内在原因,从而为解决变压器差动保护误动提供解决对策,本文分析了CT饱和对变压器差动保护差动电流二次谐波含量、间断角的影响,并结合电力系统运行实际,分析了不同情况下和应涌流导致变压器差动保护误动的可能性。研究表明,并联和应涌流不易导致变压器差动保护误动,串联和应涌流容易导致变压器差动保护误动。论文最后提出了一种识别和应涌流的新方法,用于正确闭锁变压器差动保护,以防止和应涌流引起的误动。更多还原

【Abstract】 Travelling wave-based protection is a perfect protection principle not only for it is free from the transition resistance and fault location theoretically, but also for it has an ultra high speed operation characteristic. Many travelling wave-based protection principles have been presented. Most of these protection principles aim at the transmission line faults under normal conditions taking no account of the influence of circuit breakers closing, especially the influence of asynchronous closing on the validity of protection actions. In order to improving travelling wave-based protection and impelling its practicality, an in-depth analysis to the characteristics of travelling waves caused by breakers closing, together with new method for the travelling wave closing protection, is essential.Recently, a chain of differential relays mal-operation events due to transformer sympathetic inrush when a nearby transformer is energized have been reported. But up to now, the investigations about sympathetic inrush mostly focus on its generation and change characteristic. However, the factors considered are to some extent different from power system practice. Moreover, the inherent reason for the mal-operation mentioned has not been cognized thoroughly. Therefore, it is urgent to have a further research on sympathetic inrush, and to present new measure to improve transformer differential protection after mastering the new rules of sympathetic inrush.The paper studies the two aspects described above. By analyzing characteristics of travelling wave caused by breakers closing, a novel travelling wave protection method accounting for breakers asynchronous closing is presented. On the other hand, by researching new change rules of sympathetic inrush and inherent reason for the mal-operation of transformer differential relays, a novel method which can not only identify sympathetic inrush correctly but also reduce the mal-operation probability is presented.In order to obtain exactly and quickly the polarity and magnitude relationships between forward travelling waves and backward travelling waves under various conditions such as different trouble spots, different fault types and different transition resistance, a new method to calculating the reflection coefficient and the inter-refraction coefficient of every mode under different closing sequence of three-phase breakers, is proposed. Analysis results show that forward travelling waves have the same polarity as backward travelling waves if faults are at the middle of lines. However, if faults are at the end of lines, the polarity relations between forward travelling waves and backward travelling waves depend on fault type, transition resistance and trouble phase closed first or not. In the case of big transient resistance and fault phase breaker closed firstly, or in the case of small transient resistance and fault phase breaker closed secondly, the polarity of forward travelling waves is different from that of backward travelling waves. Thus, the polarity relations are the same with those caused by closing unload lines. As a result, the existing methods will be invalid.A new closing protection accounting for breakers asynchronous closure is presented. The new closing protection is valid not only to the faults at the middle of lines but also to the faults at the end of lines. The new method base on the theory that the reflect coefficient of current travelling wave is–1 if the transmission line is fault-free. Whereas the reflect coefficient of current travelling wave is not equal to–1 if switching into faulted line. Thus, the new method can ensure that the relays will operate correctly in any case theoretically.The transformer sympathetic inrush and its change are influenced by many factors. However, the change rules of sympathetic inrush are not mastered completely because the sympathetic inrush between two different capacity transformers and transformer on load are not analyzed in detail. Aiming at those problems, the characteristics of series and parallel sympathetic inrush are compared, and the effects of load on sympathetic inrush are analyzed as a keystone. As a result, the new change rules of sympathetic inrush are explored which are as the base to recognizing inherent reasons for the mal-operation of transformer differential relays caused by sympathetic inrush.In order to discover the real reason for mal-operation of transformer differential relays caused by sympathetic inrush, the paper analyzes the second harmonic proportion of sympathetic inrush and excitation inrush firstly. Then, the effects of CT saturation on the second harmonic proportion and dead angle of sympathetic inrush are studied. Finally, the influences of Y-delta transform by CTs are analyzed. The results show that the second harmonic proportion and dead angle of sympathetic inrush are similar to excitation inrush. But the decay of sympathetic inrush is more slowly and sympathetic inrush will lead to CT saturation more easily. Consequently, the sympathetic inrush cannot be measured correctly, and transformer differential relays would mal-operate.To confirm the inherent reason for mal-operation of transformer differential relays caused by sympathetic inrush and obtain a countermeasure, the influences of CT saturation on the second harmonic proportion and dead angle of differential current are investigated. Furthermore, the possibility of differential relays mal-operation caused by sympathetic inrush is analyzed accounting for power system practice. The investigation shows that parallel sympathetic inrush has a little effect on differential relays mal-operation whereas the series sympathetic inrush is easy to lead differential relays mal-operation. Finally, a new method for identifying sympathetic inrush is proposed to block differential relays correctly and avoid mal-operation caused by sympathetic inrush.更多还原