基于测量阻抗电阻分量符号的“网孔型”柔直电网线路纵联保护

Line pilot protection of a mesh DC grid based on the sign of the resistance component in measured impedance

对于限流电抗器装设于换流站出口的“网孔型”柔性直流电网而言,线路之间无边界存在,基于边界效应的保护不再适用。同时,传统的差动类保护存在延迟长和严格通信同步的问题。为此,提出一种基于测量阻抗电阻分量符号的纵联保护方案。通过对“网孔型”直流电网的Peterson等效电路进行分析发现,当发生区内故障时,线路两端的测量阻抗电阻分量符号相同,而当发生区外故障时,二者符号相反。根据这一特征,利用连续小波变换(continuous wavelet transform,CWT)提取测量阻抗的实部并构造保护判据。理论分析和仿真结果表明所提保护方案能够可靠、快速地识别各种类型的直流线路故障,具备耐高阻和强噪声的能力,且无需双端数据的严格同步。

For a mesh DC power grid with current-limiting reactor installed at the outlet of a converter station,there is no boundary between the lines,and protection based on the boundary effect is no longer achievable.In addition,traditional differential protection has problems with long delays and strict communication synchronization requirements.Therefore,a pilot protection scheme based on the sign of the resistance component in measured impedance is proposed.Through analysis of the Peterson equivalent circuit of a mesh DC power grid,it is found that when an internal fault occurs,the signs of resistance component in measured impedance at both ends of the line are the same,while when an external fault occurs,the two signs are opposite.According to this characteristic,the real part of the measured impedance is extracted by continuous wavelet transform(CWT),and a protection criterion is constructed.Theoretical analysis and simulation results show that the proposed protection scheme can identify various types of HVDC line faults reliably and quickly,and can withstand high resistance and strong noise,without the need for strict synchronization of double-end data.