适配换流器极限耐受能力的多端柔直电网非边界依赖型主保护判据研究

多端柔直电网具有强健拓扑结构和灵活输电方式，但相对脆弱的换流器极限耐受能力以及直流线路间的互联互通增加了选择性故障隔离的难度。在直流断路器走向工程化的背景下，利用继电保护实现故障的超高速选择性切除已是大势所趋。然而，目前所用保护原理需将限流电抗器置于线路两侧以构造保护边界，既增加投资与运维成本、降低系统动态响应性能，也无法彻底解决保护所面临的选择性与灵敏性、快速性与可靠性之间的矛盾。为此，本项目拟在厘清换流器极限耐受能力、揭示保护速动性指标要求的基础上，分别针对长线路和中短线路，研究提出适配其故障特性和保护动作速度要求、并彻底摆脱对被保护对象“边界特性”依赖的全新主保护原理。在此基础上，研究上述两种保护应用于不同长度线路时的动作性能及其可行配合方式，以期实现对不同柔直线路的普适性。项目预期成果可减少柔直电网投资、解决追求保护动作性能与维持柔直电网稳定运行之间的矛盾，提升柔直电网的安全水平。

The VSC-based Multi-terminal DC (VSC-MTDC) has a strong structure and a flexible power transmission capability, while the comparatively low critical endurance capability of its converter, and the interconnection of the DC transmission lines make it more difficult for the selective fault isolation. As the DC Circuit Breaker (DCCB) related technique is growingly mature currently, it has become the current situation to isolate the fault employing the ultra-high-speed protective relaying. However, the realization of the existing protections is mainly based on the setting of the fault-current-limiting reactor on the two sides of the DC lines (boundary component), which not only increases the investment and maintenance cost but also reduces the dynamic response of the system. Besides, the contradiction between the protection selectivity and the sensitivity, and that between the fast-trip capability and the reliability is still left unsolved. To solve this problem, this project will firstly make it clear how long the critical endurance time is for the converter. Based on the revealed operating speed index, a sort of innovative protection schemes independent on the boundary component will be established according to the fault characteristics and the operating speed requirement for the long-distance lines and the medium/short-distance lines, respectively. On this basis, the performance and the coordination strategy of the above protections and will be investigated under the different length of lines, to make the proposed protections more adaptive to different transmission lines in the VSC-MTDC. The achievements of this project will cut down the investment of the VSC-MTDC, solving the contradiction between the pursuit of protection performance and the requirement of stable operation, providing a safer operating condition for the VSC-MTDC.