There is larger effect of single-phase reclosure sequence on ultra-high voltage AC/DC parallel system's transient stability. To discuss the inherent mechanism of this issue, single generator-ultra-high voltage AC/DC parallel transmission-infinite bus system is constructed, and equivalent AC impedance of DC system is derived based on switch function method and thus electromagnetic power expression is obtained. By analyzing the changing characteristic of power angle during the whole process that single-phase permanent fault is occurred, single-phase breaker is tripped, reclose to permanent fault and three phase breaker is tripped, influence of single-phase reclosure sequence on system's transient angle stability is described. Setting criterion of reclosure sequence to decrease acceleration area and enhance system's transient stability is proposed, i.e. to reclose on the terminal with smaller equivalent impedance of system. Correctness and effectiveness of the criterion is simulated in single generator-ultra-high voltage AC/DC parallel transmission-infinite bus system and south China power grid in 2010.%重合闸时序对特高压交直流并联系统暂态稳定性有较大的影响,为探讨其内在机理,构造了单机特高压交直流并联输电无穷大系统,采用开关函数法推导出直流系统的等值交流阻抗,得到了系统电磁功率的解析表达式.通过分析一回交流线路发生单相永久接地故障、故障相跳闸、故障相重合于永久故障、三相跳闸的整个过程中发电机的功角变化特性,利用等面积法则从机理上阐述了重合时序对系统功角稳定性的影响.提出了单相重合时序设置判据,即使系统等值阻抗较小的一侧首先重合,以期减小系统的加速面积,提高并联系统的暂态功角稳定性.在单机特高压交直流并联无穷大系统和2010年南方电网中,对该判据的正确性和有效性进行了仿真验证.
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