多端柔性直流电网保护关键技术

多端柔性直流电网直流故障后故障电流快速上升、无自然过零点等特点使得直流线路保护和故障处理技术成为柔性直流电网发展的关键技术难点。理论分析了多端柔性直流电网线路保护的特殊性,借鉴传统直流输电线路保护原理和点对点式柔性直流输电线路保护原理的研究现状,对多端柔性直流电网线路保护的发展方向进行了探讨。同时,全面分析了各类直流故障隔离方法的基本原理,从故障隔离能力、经济性、控制保护耦合影响等多个方面阐述了其进一步的发展趋势。最后,考虑到架空线路输电的应用前景,设计提出了一种适用于点对点式柔性直流输电系统、具有低电流危害的新型故障重合闸判断方法,较现有重合闸策略而言,该方法重合于永久性故障时能够彻底避免对系统的二次过电流冲击。在此基础上,讨论了多端柔性直流电网对重合闸策略的性能要求。

Key Techniques for Protection of Multi-terminal Flexible DC Grid

Direct current(DC)line protection and fault handling technology are the key technical difficulties of the multi-terminal flexible DC gird due to the fault characteristics including high-speed rising of the fault current and the lack of natural zero crossing point. The particularity of the DC line protection in the multi-terminal flexible DC grid is analyzed. Considering the protection principle of the line commutated converter based DC system and the development of the protection for the point-to-point flexible DC system, this paper discusses the developing trend of the line protection for the multi-terminal flexible DC grid. Meanwhile, different kinds of the DC fault isolation are introduced, further developing direction is also discussed considering the fault isolation capability, investment and the coupling influence between the protection and control. Finally, a novel reclose strategy of the DC fault on overhead line for the point-to-point DC system is proposed, which does not lead to the second overcurrent damage during permanent faults. Afterwards, the performance requirements for the reclose strategy of the multi-terminal DC grid are discussed. This work is supported by National High Technology Research and Development Program of China(863 Program)(No. 2015AA050101).