新能源及直流输电系统邻近区域交流线路出口故障保护原理研究

If a short-circuit fault occurs at the exit of AC line, which is close to new energy source or HVDC power transmission system, it will be difficult for the traditional power-frequency protection to operate correctly and reliably. The high-frequency transient protection is easily influenced by interference signals, and it also lacks targeted and thorough research. This project is mainly based on the fault characteristics of "new power source" such as new energy source and HVDC transmission systems and the fault characteristics independent of the source. On the one hand, on the basis of revealing the evolvement laws of "new power source" transient voltage when AC line faults occur, the relationship between "new power source" transient voltage and the measured electrical quantities can be analyzed, then a novel protection scheme for the exit of AC line can be proposed. On the other hand, based on revealing the association between the traveling direction of faulty power and transient propagation of electrical quantities, the difference of space-time characteristics of electrical quantities distribution can be analyzed when positive and negative exit faults occur. Then another novel protection scheme for the exit of AC line can be proposed. According to the theory of ETPTL, filters can be used to lower the frequency of electrical quantities, enhancing the adaptability and reliability of the new protection. Therefore, the quick and reliable clearance of the exit fault in the AC-DC hybrid power grid with large-scale new energy source integrated can be realized.

新能源和直流输电系统的邻近区域交流线路出口短路，输电线路工频量保护难以正确可靠地切除故障，高频暂态量保护易受干扰信号影响而且尚缺乏有针对性的充分深入研究。本项目从基于新能源和直流输电系统等“新型电源”的故障特性和不依赖电源故障特性两方面开展研究：在揭示交流线路故障时“新型电源”暂态电势短时演化规律的基础上，分析提供保护安装处故障穿越功率的“新型电源”暂态电势与保护检测电气量的相互关系，提出交流线路出口保护新原理；在揭示了保护安装处故障功率穿越方向与电气量暂态传播过程的关联特性基础上，分析交流正、反方向出口故障时交流线路保护近区电气量分布的时空特性差异，提出交流线路出口故障保护新原理。项目研究中依据输电线路等传变原理，采用滤波器降低保护新原理计算的电气量频率，以增强保护的适应性和可靠性，从而实现大规模新能源接入的交直流混联电网中交流输电线路保护出口严重故障的可靠快速切除。

针对大规模新能源接入的交直流混联电网交流线路保护出口故障判别难题，项目分析了新能源、直流输电系统等“新型电源”邻近区域的交流线路故障特性，从“新型电源”与保护检测电气量的关联特性和故障功率穿越方向与电气量暂态传播过程的关联特性两个方面开展研究工作。揭示了dq坐标系下直驱风电、光伏等逆变型电源送出线故障后短时间内线路两侧故障电流d轴分量的变化特征，提出了基于d轴电流短时变化特征的送出线保护近区故障方向元件，通过计算故障后短时间内保护安装处d轴电流变化量平均值判别故障方向；建立了双馈风机为代表的双馈型电源故障后暂态等值电路，定义了双馈风机的暂态等值电势，指出双馈风机暂态等值电势在故障后存在短时惯性，进而提出一种利用双馈风电场等值暂态电势短时惯性的线路出口故障方向判别方法，利用系统等值阻抗上“记忆电压降落”和“计算电压降落”在正方向和反方向故障时变化趋势的差异确定故障方向；分析了高压直流换流站故障电流特性，提出了基于计算电压降落和测量电压降落变化趋势比较的故障方向判别方法，能够适用于换流站不同交流出线结构；分析了出口故障初期交流线路保护近区电气量分布的时空特性，揭示了交流输电线路低频电压沿线近似线性分布特征，阐明了整定点电压和保护安装处电压正方向和反方向故障时的演化规律，提出了瞬时值变化量方向保护原理，通过比较计算的整定点电压变化量和保护安装处电压变化量实现故障方向判别，在故障后数毫秒内快速准确判别故障方向，能够适用于不同类型的新能源电源接入系统；进一步完善了新能源及柔性直流系统的动模实验平台，对所提新能源及直流输电系统临近区域交流线路出口故障保护算法进行了动模试验验证。通过上述研究，形成了新能源和直流输电系统临近区域交流线路出口故障保护的工作原理与技术方案，完成了动模试验验证工作，为理论成果的实用化奠定了良好的基础。