并联型混合多端直流线路单极-双极混合运行方式下的故障行波特性

单极-双极混合运行是并联型混合多端直流输电系统中非常重要的一种运行方式,可以最大程度减小换流站故障或检修带来的功率损失,研究该方式下的直流线路故障行波特性及其对行波保护的影响具有重要意义。该运行方式下直流线路间存在一个不对称折反射界面,针对该界面的结构特点进行了行波折反射特性的理论和仿真分析;在此基础上研究了单极接地故障时的故障行波传播特性,并结合工程实际分析了其对行波保护的影响。研究结果表明:模量之间的交叉折射是造成单极双极混合运行方式下故障行波传播特性不同的主要原因;就基于模量的行波保护判据而言,单极双极混合运行方式将造成行波保护动作量减小,需要在定值整定中予以考虑。

Faulted Traveling Wave Characteristics of Parallel Hybrid Multi-terminal DC Lines Under Unipolar-bipolar Hybrid Operation Mode

Unipolar-bipolar hybrid operation mode is a kind of very important operation mode in the parallel multi-terminal HVDC transmission system,which can minimize power loss caused by faults or maintenance in converter station,and it is of great significance to study the faulted traveling wave characteristics of the line and the impact on traveling-wave protection under the operation mode.Due to an unsymmetrical interface between the lines,the theory and simulation analysis of the refraction and reflection characteristic is carried out according to the structural characteristics.Then,the traveling wave propagation characteristics of single-pole-to-ground fault are studied,and the influence on traveling wave protection is analyzed combining engineering practice.The results show that the inter-refractive of the modulus traveling wave is the main reason for the difference of the faulted traveling wave propagation characteristics in the unipolar-bipolar hybrid operation mode.In terms of the traveling wave protection criterion,the unipolar-bipolar hybrid operation mode will weaken the traveling wave,which needs to be considered in traveling wave protection setting.