继电保护同时具有“设备/元件属性（简称设备属性）”和“电网/系统属性（简称系统属性）”。交直流混联系统故障的系统属性进一步增强、放大，一方面扩大了电力系统故障分析的空间尺度和时间尺度；另一方面可能引发故障特征在交直间传递、耦合甚至变异。实际运行经验表明，这已成为制约继电保护乃至整个电网安全运行的瓶颈。.本项目针对交直流混联系统故障系统属性对直流保护的挑战，从直流响应本质核心：阀状态和控制模式及其转化入手建立故障分析模型，对故障系统属性特性、关联因素及其作用边界展开分析，在此基础上提出直流保护协调优化策略。从故障的系统属性带来的影响和约束出发对继电保护动作行为评估无疑是一种新思路，突破了传统保护一时一地分析的局限性，对提升直流保护技术水平和驾驭交直流混联系统能力，防止复杂大系统灾变事故的发生具有重大意义。

Protection has both "equipment / component attribute (referred to equipment attribute)" and "grid / system attribute (referred to as the system attribute)." The system attribute is further enhanced in AC-DC hybrid system. It expand the spatial and temporal scales of power system fault analysis. It may lead fault feature to transmission, coupling and even variation between AC and DC system. Actual operating experience has shown that this has become a bottleneck restricting the protection and the safe operation of the power grid..This research aims at the challenges of fault system attribute to HVDC protections in AC-DC hybrid system. According the response from the DC core essence: responding and switching of valve statuses and control modes, the HVDC fault analysis models are setup. Then the impact and factors and their associated side effects of system attributes are analyzed. The dynamic characteristics of the HVDC relaying quantities are firstly studied considering the effect of fault condition, system operation condition, and control system behavior. The study results clarify the boundary, constraint condition, and function of the protection criterions, which in turn gives a basis for the setting determination and optimization of HVDC protective relaying. By doing so, we effectively solve the problem of lacking efficient method for the setting determination and performance evaluation of HVDC protections, and incorporate the problem into the framework of conventional power system protection.