Abstract DC filter is an important electrical apparatus to restrain harmonics in a line-commutated converter based HVDC (LCC-HVDC) system. The used differential protection for DC filters has poor selectivity and insufficient sensitivity to identify ground faults of DC-filter high voltage capacitors (DFHVCs). Based on virtual capacitance, a novel ground-fault protection for DFHVCs is proposed in this paper. According to the equivalent circuit of DC filter in a LCC-HVDC system, virtual capacitance characteristics are analyzed under different ground faults of DFHVC. Then, these characteristics are used for constructing protection scheme to identify DFHVC ground faults from external faults. A ±500 kV HVDC system built in PSCAD/EMTDC is used to verify the performance of the proposed protection. Comprehensive simulations show that the proposed protection can reliably identify DFHVC ground fault in time domain and is immune to fault resistance, fault location, measurement error and DC filter structure. Moreover, it is noted that the protection can identify a ground fault of DFHVC during the whole fault period and is of high reliability, making it valuable and prospective for applications in LCC-HVDC system.

中文翻译：

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基于虚电容的直流滤波高压电容器接地故障保护

摘要 直流滤波器是基于线路换向换流器的高压直流（LCC-HVDC）系统中抑制谐波的重要电气设备。用于直流滤波器的差动保护选择性差，灵敏度不足，无法识别直流滤波器高压电容器（DFHVC）的接地故障。本文基于虚拟电容，提出了一种新型的 DFHVC 接地故障保护。根据LCC-HVDC系统中直流滤波器的等效电路，分析了DFHVC不同接地故障下的虚拟电容特性。然后，这些特性用于构建保护方案，以从外部故障中识别 DFHVC 接地故障。内置于 PSCAD/EMTDC 的 ±500 kV HVDC 系统用于验证建议保护的性能。综合仿真表明，所提出的保护可以在时域内可靠地识别 DFHVC 接地故障，并且不受故障电阻、故障定位、测量误差和直流滤波器结构的影响。此外，该保护可以在整个故障期间识别DFHVC的接地故障，可靠性高，在LCC-HVDC系统中的应用具有价值和前景。