【作者】 刘洪顺；

【导师】 李庆民；

【作者基本信息】 山东大学 ， 高电压与绝缘技术， 2010， 博士

【摘要】 随着我国电网规模的扩张、电力系统中负荷的迅速增长以及大容量机组不断投入运行,短路电流水平的日益提高严重威胁着电力系统的安全、可靠与稳定运行。采用调整电网结构、改变系统运行方式等传统短路电流限制措施,尽管可在某种程度上抑制短路电流,但无一例外地将对电网运行的灵活性、经济性和可靠性带来不同程度的负面影响。因此,研究性能优良、经济合理的新型故障限流器(Fault Current Limiter, FCL)是大势所趋,对我国电网发展具有重要的现实意义和应用价值。本文旨在发展基于常规电气设备或元件的非超导、非电力电子型故障限流新技术,重点研究其在高压电力系统应用所面临的科学与关键技术问题。研究内容包括以下几个方面：基于ZnO避雷器和放电间隙的经济型故障限流拓扑优化及其数字化在线监测与控制系统研究；基于永磁偏置原理的经济型故障限流技术的探索研究,涉及材料选型、运行机理分析、等效建模与拓扑优化等；经济型故障限流器应用对高压电力系统的综合影响研究,涉及暂态稳定、断路器开断特性、自动重合闸技术等方面。在综合分析现有串联谐振型FCL优缺点的基础上,提出了基于ZnO避雷器和并联放电间隙的故障限流新拓扑,并开展了中低压模拟实验研究,进一步建立了110kV等级限流器的总体设计方案及其数字化在线监测、诊断、保护、触发与控制系统。此研究工作为超高压等级ZnO避雷器式FCL样机的研制奠定了理论基础和技术依据。本文还就基于永磁偏置饱和原理的经济型故障限流技术开展了探索研究。针对系统正常状态和故障限流状态,研究了永磁体与软磁铁心的工作点配合准则；在综合分析多种典型软磁材料和永磁材料的磁性能、机械性能和经济性能的基础上,提出了软磁铁芯和永磁体材料的选择原则；详细分析了不同永磁饱和型故障限流拓扑的静态和动态场、路特性,建立了等效磁路分析模型；开展原理性实验研究以寻找提高永磁体偏置能力以及FCL限流性能的有效技术途径,为实现永磁饱和型FCL的高压大容量化提供了基础依据。短路故障引发的暂态功角振荡以至失稳可能威胁到电网的安全运行,而FCL在限制短路电流的同时也参与了系统的暂态过程,其对电网暂态行为的影响值得研究。针对安装经济型FCL的单机-无穷大系统,利用等面积定则详细分析了其暂态物理过程,并进行了单机和多机系统的仿真验证,结果表明：安装经济型FCL故障限流器,可有效抑制摇摆曲线的振荡幅度并缩短衰减周期,延长系统的极限切除时间,提高系统的暂态稳定能力。安装FCL可有效降低电力系统的短路电流水平和对高压断路器的遮断容量要求,但也可能造成更加苛刻的开断条件。针对安装经济型FCL的系统发生出线故障和近区故障的情况,基于理论分析与数学推导,建立了描述断路器恢复电压上升率与限流比、杂散电容以及近区故障距离之间关系的数学表达式。基于这些理论公式,研究了各主要参数对恢复电压上升率的具体影响,并与文献中的有关仿真结果进行了比较,验证了分析方法的有效性。研究结果为经济型FCL的参数优化和高压断路器开断特性的选型提供了分析基础和理论依据。进一步分析了经济型FCL不同限流比对失步故障电流的影响,得到了单回和双回接线方式下输电线路临界长度的计算方法。提出了失步故障时断路器开断苛刻度的概念,导出了断路器开断苛刻度与FCL限流比的数学表达式,并研究了FCL限流比和杂散电容对断路器开断苛刻度的具体影响。分析结果表明,为有效降低断路器对失步故障的开断苛刻度,应尽量避免将FCL的限流比设计在0.5附近,并通过结构设计尽可能地增大FCL的杂散电容。在安装有氧化锌避雷器式FCL的超高压线路中,因FCL中串联电容器的存在,可能导致潜供电流中含有幅值较大、衰减较慢的低频分量,易造成潜供电弧不易自熄,使单相重合闸成功率降低。本文针对安装氧化锌避雷器式FCL的500 kV输电系统,利用电磁暂态计算程序分析了FCL旁路开关的不同断开时间和不同弧道电阻对潜供电流特性的影响。基于等效阻抗网络和拉普拉斯变换方法,研究了潜供电流自然振荡频率与衰减系数的变化情况,从理论上解释了潜供电流低频分量的产生机理。提出了氧化锌避雷器式FCL与单相自动重合闸的时序配合策略,并进行了仿真验证结果表明,该策略可有效消除可能的潜供电流低频分量对单相自动重合闸的不利影响,既能确保自动重合闸操作的正常时序,又能兼顾故障限流器的自恢复特性。本文研究成果进一步发展了电力系统故障限流技术的基础理论和分析方法,对高压大容量经济型故障限流器的科学研究与工程应用具有重要意义。更多还原

【Abstract】 With rapid increase of the power loads as well as continuous incorporation of the new-built large capacity generators, the short circuit current level of HV power systems is getting more and more critical. As a result, the operational safety, reliability and stability of the power systems are unprecedentedly threatened. To account for this arduous issue, some traditional measures to limit fault current have been utilized, such as system reconfiguration, operating mode modification and so on. Though these solutions definitely suppress the fault current level to a certain extent, they also render negative impacts on the flexibility, economy and reliability of the power systems. Hence, investigation on developing new types of fault current limiters with preferable performance both technically and economically is an indispensible and irresistible trend for the time being, which is extremely significant and invaluable for development of nowadays power grids in China.Based on conventional electrical devices and components, some novel fault current limiting technologies without superconductors or power electronic equipments were systematically investigated in this dissertation. The principal research work focused on the key fundamentals with a view to facilitating their applications in the high voltage power systems. The research contents cover several aspects as follows:a)Optimization of the economic-type fault current limiting topology based on ZnO Arresters and a Discharge Gap, as well as development of a digital on-line monitoring & comprehensive protection scheme; b)Exploratory research on an economic-type fault current limiter based on permanent-magnet-biased saturation, including material selection, operating principle analysis, equivalent modeling and topological optimization; c)Comprehensive analysis on the impact and interaction of the economic-type fault current limiters with the high voltage power systems, such as transient stability, interrupting characteristics of circuit breakers, single-phase autoreclosure and so on. Taken into account of the advantages of different series resonant FCLs, a new fault current limiter topology based on ZnO Arresters and a Parallel Discharge Gap was proposed, and its fault current limiting characteristics was verified by laboratory experiments. Furthermore, a detailed design scheme for 110kV FCLs was presented and thereby a digital on-line monitoring, diagnosis, protection, triggering and control scheme was established accordingly. The research results provide fundamental theory and technological reference for development of the ZnO Arrester-based FCLs targeted for extra-high voltage transmission lines.The economic-type fault current limiting technology based on permanent magnet biased saturation, noted as PMFCL, was explored in this dissertation to provide governing principles. With respects to normal and fault modes, the cooperation criterion for operating points of the permanent magnets and the magnetic cores was investigated. After comprehensive analysis in terms of magnetic characteristics, mechanical performance and economic property of different kinds of magnetic materials, a material selection guideline for magnetic cores and permanent magnets was proposed. Further, the equivalent magnetic circuit models were established based on the static and dynamic magnetic field-circuit characteristics of different PMFCL topologies. Some rationale experiments were carried out as to find effective ways to improve the permanent magnet biased performance and fault current limiting characteristics of the PMFCLs, which also presents the foundation to develop high voltage and large capacity PMFCLs.Power-angle transient oscillation or instability of the power grids caused by short-circuit fault will threaten the system safety. When a fault occurs, the FCLs will function to limit the fault current and also influence the system’s transient process, which needs further investigation and verification. With respect to a typical one-machine infinite-bus installed with economic-type FCLs, the transient physical process was analyzed in details by using the Equal Area Criterion. The theory analyses were verified by MATLAB simulations for both one-machine and multiple-machine systems. Both theoretical analysis and simulation results show that, the installation of economic-type FCLs can effectively suppress the oscillatory amplitudes of swing curves, reduce the decaying period, extend the critical clearing time and hence improve the transient stability of the power systems.Installation of FCLs in the power systems can effectively suppress the short-circuit current level and thus reduce the breaking capacity requirement from HV circuit breakers, however, it may also result in more severe breaking conditions for circuit breakers. With regards to FCL terminal fault and short-line fault in power transmission lines installed with economic-type FCLs, mathematical formulas were presented, based on theoretical analysis and deduction, as to properly describe the relationship between the rate of rise of recovery voltage (RRRV) of circuit breakers and the current limit factor, the stray capacitance as well as the short-line fault distance. According to these formulas, detailed computations were carried out to fully account for the concrete impacts on the RRRV from every principal parameter, and were correlated with the conclusions drawn by simulations in previous publications available, which accordingly well verified the proposed analyzing methodology. The research results present analytical basis and theoretical reference for parameter optimization of the inductive FCLs and also for reliable selection of the breaking characteristics of HV circuit breakers.Especially for the out-phase-faults, the impact of FCLs on the interruption of out-phase-fault current was analyzed and the methods for computing the critical length of the transmission lines were presented. The conception of interrupting severity of circuit breakers was proposed and the influence of the current limit factor and the stray capacitance on the interrupting severity of circuit breakers was investigated in details. The above research results show that, the design of current limit factor should avoid around 0.5 so as to reduce the interrupting severity of circuit breakers, and it is better to effectively increase the stray capacitance of the FCLs by optimizing the structure design. For the extra-high voltage transmission lines operational with ZnO arrester-based FCLs, the capacitor of the FCLs may contribute to the low frequency current components of the secondary current with big amplitude and slow attenuation. With regard to a 500 kV long-distance transmission line installed with ZnO arresterbased FCLs, the influence of both the FCL bypass switch operation and the different arc resistances on the characteristics of the secondary arc current was analyzed by EMTP (electromagnetic transients program) simulations. The decay factor and the oscillation frequency of the secondary arc current were computed based on the equivalent impedance network and Laplace transformation, with a view to elucidating the physical nature of the low frequency oscillation of the secondary arc current. A time-sequence coordination scheme between the single-phase autoreclosure (SPAR) and the FCL operation was proposed and verified by concrete simulations. The results indicate that, the proposed scheme can effectively eliminate the side impact caused by the low frequency current components on the SPAR, and can guarantee the normal operational sequence of a SPAR as well as the self-restoration of a FCL.The research achievements in the dissertation have further developed the fundamental theory and analyzing methodologies of the fault current limiting technology, and present great significance for both the scientific research and engineering application of the high voltage and large capacity economic-type fault current limiters.更多还原