基于固有模态能量熵的多端混合直流线路方向暂态保护研究

Directional Transient Protection of Multi-terminal Hybrid DC Lines Based on Inherent Mode Energy Entropy

特高压多端混合直流输电线路首端整流侧边界、线路末端逆变侧边界不对称,T区边界不明显,线路保护故障区间的准确判别是目前亟需解决的重要问题。该文以昆柳龙特高压三端混合直流输电系统为研究对象,将保护元件安装于T区左右两侧,提出一种基于固有模态能量熵的多端混合直流线路方向暂态保护方法。论文分析特高压多端混合直流输电线路首端整流侧边界、线路末端逆变侧边界频率特性。根据T区两侧保护元件检测到的故障电流暂态能量的正负特性,提出T区左右两侧故障方向判据。利用互补集合经验模态分解(complementaryensembleempiricalmode decomposition,CEEMD)对故障暂态电流进行不同尺度分解,根据固有模态能量熵提出线路首端整流侧及线路末端逆变侧区内、外故障判据,解决了提取单一信号频带检测故障的局限性。分析和仿真结果表明,该保护方案仅利用T区左右两侧的保护元件就能实现特高压多端混合直流输电线路全线速动保护,且具有较好的耐受过渡电阻能力。

The boundary between the rectifier side at the head end and the inverter side?at the end of the UHV multi terminal hybrid DC transmission line is asymmetric,and the boundary of the T-zone is not obvious.The accurate identification of the fault zones of the line protection is an important problem to be solved at present.Taking Kun-Liu-Long UHV three terminal hybrid DC transmission system as the research object,this paper proposes a directional transient protection for multi-terminal hybrid DC lines based on the inherent mode energy entropy by installing the protection components on the left and right sides of the T zone.The frequency characteristics of the rectifier side boundary at the head end and the inverter side boundary at the end of the UHV multi-terminal hybrid DC transmission line are analyzed.According to the positive and negative characteristics of the transient energy of the fault current detected by the protection elements on both sides of the T zone,the criterion of fault directions on both sides of the T zone is proposed.The fault transient current is decomposed in different scales using the Complementary Ensemble Empirical Mode Decomposition(CEEMD),and the internal and external fault criteria of the rectifier side at the head end of the line and the inverter side at the end of the line are proposed according to the inherent mode energy entropy,which solves the limitation of extracting a single signal frequency band to detect faults.The analysis and simulation results show that this protection scheme is able to achieve the full line quick action protection for the UHV multi-terminal hybrid DC transmission lines only by using the protection elements on the left and right sides of the T zone,having a good ability to withstand the transition resistance.