基于单端电气量的多端柔性直流配电系统暂态保护

随着配电系统结构的发展与变化,传统交流配电系统、高压直流输电系统的保护原理无法适用于多端柔性直流配电系统。目前所提直流配电线路的保护方案有2种思路:基于线路两端信息和基于线路单端信息。前者需要通信通道,要求两端数据的同步,动作速度慢;后者需要构造保护边界,增加系统经济成本。基于此,提出了一种基于单端电气量、无需构造保护边界的多端柔性直流配电系统暂态保护方案。首先,分别计算线路一侧的正、负极暂态电压与其正常稳态电压的标准差系数识别故障极。然后,分析发生区内故障时各电气量的时域解析关系,分别推导出单、双极故障时的微分方程以计算故障距离,从而实现区内、外故障的快速、可靠识别。最后在MATLAB/Simulink中搭建了仿真模型。仿真结果表明,所提保护方案在各种故障情况下仅基于本地信息即可有效识别故障极和区内、外故障,有较强的抗过渡电阻及抗干扰能力,满足直流配电网对保护速动性与选择性的需求。

Transient protection based on single-end electrical signals for multi-terminal flexible DC distribution system

With the development of distribution system structure, the protection principles of AC systems and conventional DC transmission systems are not applicable to the multi-terminal flexible DC distribution system. At present, there are two concepts of protection schemes proposed for DC distribution systems: one is based on the information of both line ends, which requires communication channel for synchronizing the information of both line-ends, resulting in slow speed; the other is based on the information of single line-end, which has to construct the protection boundary, resulting in increased cost. A protection scheme is proposed for the multi-terminal flexible DC distribution system, which is based on the single-end electrical transient signals and does not need protection boundary. The coefficients of variances between transient voltages and normal steady-state voltages are calculated for the positive and negative poles of one side to identify the faulty pole. The time-domain analytical relationships among electrical signals during an in-zone fault are analyzed to derive the differential equations of single-polar or bipolar fault for calculating the fault distance to quickly and reliably identify the in-zone and out-zone faults. A MATLAB/Simulink simulation model is built and the simulative results show that, the proposed scheme can effectively identify the faulty pole, in-zone fault and out-zone fault only based on the local information in different fault conditions; it is immune to transition resistance and has better anti-interference ability; and it can satisfy the requirements of DC distribution network for the protection rapidity and selectivity.