烟墩–天山750kV双回线路不平衡电流的计算与分析

Calculation and Analysis on Unbalanced Currents of Yandun-Tianshan 750kV Double-circuit Transmission Lines

基于电磁暂态仿真程序(electro-magnetic transient program,EMTP),以750kV烟墩-天山线路(烟天线)为例,文章对平行架设且不换位的双回线路不平衡电流问题进行计算与分析。研究表明,零序环流是导致烟天线零序电流较大进而保护报警的主导因素。调整平行架设双回线路的相序排列方式(推荐逆相序排列),是改善零序环流问题的有效措施。逆相序下两回线路的地线配置相同且按镜面对称排列,可以消除零序和负序环流的影响。条件允许时,推荐采用2根连续地线位于内侧、2根分段地线位于外侧的布置形式。采用同相序(或相序4、5、6)且回间距离较近时,可能出现严重的零序环流。在零序环流分量远大于零序直通分量且系统等值阻抗变化不大的条件下,文章提出一种估算3I0最大值的简便方法。针对不同的情况,对平行架设且不换位的双回线路不平衡电流问题提出3种对策。

Based on Electromagnetic Transient Program(EMTP),750kV Yandun-Tianshan transmission lines are taken as an example,unbalanced currents of paralleled and untransposed double-circuit transmission lines are calculated and analyzed.The research shows that zero-sequence circulating current is the main factor leading to large zero-sequence currents and then protection alarm for Yandun-Tianshan transmission lines.Adjusting phase sequence arrangement of paralleled double-circuit transmission lines(inverse phase sequence is recommended)is an effective measure to improve the problem of zero-sequence circulating current.Under inverse phase sequence,the influence of zero-sequence and negative-sequence circulating current can be eliminated when ground wire configuration of two circuits are the same and arranged in mirror symmetry.When conditions permit,it is recommended to adopt the arrangement of two continuous ground wires on the inside and two sectional ground wires on the outside.On the condition that same phase sequence(or phase sequence 4,5,6)is adopted and the distance between circuits is close,serious zero-sequence circulating currents may occur.A brief method for estimating maximum 3I0 is proposed under the condition that zero-sequence circulating component is much greater than zero-sequence through component and equivalent impedance of the system changes not much.In view of different situations,three countermeasures are put forward for the problem on unbalanced currents of paralleled and untransposed double-circuit transmission lines.