一种混合双极直流输电线路保护新原理

A new protection principle of hybrid bipolar HVDC transmission line

应用故障网络分析方法,研究了混合双极直流输电线路可能发生的各种短路故障类型,并进行了故障特性分析。根据分析结果发现:当直流输电线路发生区内故障时,整流侧与逆变侧的暂态电压和暂态电流夹角的余弦值相同;当直流输电线路区外(整流侧或逆变侧)发生故障时,整流侧与逆变侧的暂态电压和暂态电流夹角的余弦值相反。根据该故障特征,可实现区内、外故障的识别。利用小波变换提取暂态电压、电流分量。另外,故障极的暂态电压和电流的积的变化量远远大于正常极。根据此特征,进行故障选极。最后,通过电磁暂态仿真软件搭建电压不对称的混合双极直流输电系统仿真模型,对其直流输电线路设置不同故障进行仿真,利用MATLAB进行算法的验证,结果表明该保护新原理的正确性及故障选极是可行的。

By using the fault network analysis method,various types of short circuit faults that may occur on hybrid bipolar DC transmission lines are studied,and the fault characteristics are analyzed.From the analysis results,it is found that:when an internal fault occurs on the DC transmission line,the cosine of the angle between the transient voltage and the transient current of the rectifier side and the inverter side is the same;when an external fault occurs beyond the DC transmission line at the rectifier side or inverter side,the cosine of the angle between the transient voltage and the transient current of the rectifier side and the inverter side is opposite.According to the characteristics of the fault,the internal or external fault identification can be realized.Wavelet transform is used to extract transient voltage and current components.In addition,the change of the product of the transient voltage and current of the fault pole is much larger than that of the normal pole.According to this feature,an energy function criterion can be constructed to determine the fault pole.Finally,the simulation model of hybrid bipolar DC transmission system with asymmetric voltage is built by PSCAD,different fault types are set up in the DC circuit and the simulation was carried out using MATLAB.Simulation results show that the proposed protection principle is correct and the fault pole selection is feasibile.