直流双极闭锁故障下送端系统暂态过电压计算方法

针对特高压直流输电系统闭锁引起的暂态过电压严重威胁系统安全运行的问题，推导建立了直流双极闭锁后换流母线暂态电压的解析表达式。在此基础上，建立了送端交流系统电力网络等值模型，推导出了直流双极闭锁后送端交流系统内任一关键节点暂态过电压的计算方法。为判断送端新能源节点面临高压穿越问题的严重程度、提前发现系统薄弱环节，提出用阻抗比来表征节点的暂态过电压程度。在直流双极闭锁后节点暂态电压压升值随着阻抗比增大而呈现线性升高的趋势。基于DIgSILENT仿真平台，搭建了CIGRE直流输电标准测试系统和吉泉±1100 kV高压直流送端系统，验证了送端系统暂态过电压计算方法及结论的正确性。

Transient overvoltage calculation method of HVDC sending-end system under DC bipolar blocking

High voltage direct current (HVDC) transmission is an economical option for transmitting a large amount of power over long distances. Initially, HVDC was developed using thyristor-based current source converters (CSC). With the development of semiconductor devices, a voltage source converter (VSC)-based HVDC system was introduced, and has been widely applied to integrate large-scale renewables and network interconnection. However, the VSC-based HVDC system is vulnerable to DC faults and its protection becomes ever more important with the fast growth in number of installations. In this paper, detailed characteristics of DC faults in the VSC-HVDC system are presented. The DC fault current has a large peak and steady values within a few milliseconds and thus high-speed fault detection and isolation methods are required in an HVDC grid. Therefore, development of the protection scheme for a multi-terminal VSC-based HVDC system is challenging. Various methods have been developed and this paper presents a comprehensive review of the different techniques for DC fault detection, location and isolation in both CSC and VSC-based HVDC transmission systems in two-terminal and multi-terminal network configurations.