基于归一化标准面积差的多端LCC-MMC-HVDC高灵敏性主保护判据

Extra-sensitive Main Protection for Multi-terminal LCC-MMC-HVDC Based onNormalized Area Differential Criterion

整流侧采用大容量换相换流器换流器(line commuted convertor,LCC)作为功率集中送端、逆变侧采用多个全/半桥混合模块化多电平换流器(full-half-bridge modular multilevel converter,FHMMC)换流器作为多落点受端的混合高压直流输电系统是直流输电技术的重要发展方向,其主保护,特别是单端量保护的动作性能提升问题受到了广泛关注。该文从区内/外故障场景下保护安装处所感受到的首波头特征出发,理论推导并归纳不同区段线路保护安装处(包括全线长行波保护、下一区段线路的行波保护)首个前行波、反行波时/频域形态上的共性规律;利用首个反行波波头在区内/外故障场景下的形态差异,在充分考虑T区母线节点对行波折/反射、输电线路色散对波头形态的形变效应的基础上,提出一种基于归一化标准面积差的主保护判据:利用正向区内故障时的归一化面积差为正、区外故障为负的特点快速响应区内故障,并利用主动注入噪声的方式躲开反向故障防止误动。仿真及实验验证均表明,提出的保护原理在具备明确选择性的同时达到600Ω的抗过渡电阻能力,满足800 kV输电系统对灵敏性的要求。

HVDCs with a large-capacity line commuted convertor(LCC)converter as a sending end and several full-half-bridge modular multilevel converter(FHMMC)as multi-terminal receiving ends,naming the LCC modular multilevel converter based HVDC(LCC-MMC-HVDC),is a significant recent advance in the field of DC power transmission,and it has long been a hot issue for the protection technique,especially for main protection elements.In this paper,the initial wave feature of each relay location,under internal/external fault scenarios,is analyzed and summarized,and the general feature of the forward/backward traveling waves is deduced.Based on the feature difference of the initial backward wave under internal/external fault conditions,a protection criterion is put forward based on normalized area difference.Internal fault is distinguished from external ones according to the polarity of the normalized area difference,which is positive under internal fault conditions and negative in external fault scenarios.Reverse faults are avoided reliably with the help of the active inserted noise.Simulation results indicate that the proposed protection has definite selectivity,and the sensitivity can be as high as 600Ω,which is sufficient in terms of a power system of 800 kV.