【作者】 张波；

【导师】 李晓华； 李艳；

【作者基本信息】 华南理工大学 ， 电气工程， 2012， 硕士

【摘要】 由于电网中机组容量、变电站容量、负荷密度的持续增长，电网结构越来越紧密，以至于各电压等级电网中短路电流水平不断增加甚至超标。500kV电网中主变中性点串接小电抗是抑制短路电流水平的有效措施。但是，主变中性点加装小电抗后，改变了系统的零序参数，当线路发生不对称接地故障时，对故障电量的影响已成为影响交流侧继电保护定值整定并导致保护误动的不可忽视的重要因素。本文首先建立了500kV电网中单台自耦主变压器（以下简称主变）中性点串接小电抗的模型，然后从故障发生位置、加装小电抗阻值大小、输电线路长度变化三个方面着手，当500kV变电站各电压等级侧出线发生接地故障时，根据Matlab软件绘制的各零序电量的相对变化量变化曲线图，详细分析了加装小电抗前后各零序电量的变化趋势。分析可知其对零序电压的影响很微弱，对零序电流的影响较严重。进而对线路零序过流保护、主变中性点零序过流保护以及相邻线路间保护的配合受到的影响作了重点分析。在上述研究的基础上，基于环网结构的系统等值模型，定量计算了多个500kV站点自耦主变中性点经小电抗接地时各零序电量所受的影响。根据各零序电量相对变化量的变化曲线，详细分析了当故障位置发生变化时各零序电量的变化趋势。考虑到电网中需要加装小电抗的站点的数量的规模，文中设置了不同的加装情形，重点研究了其对各电量的影响是否存在叠加效应，并对线路零序过流保护、主变中性点零序过流保护受到的影响作了分析。更多还原

【Abstract】 With the continued growth of the capacity of the units and substation capacity and loaddensity in the power grid, the grid structure is becoming more and more closely. It enablesincreasing levels of short-circuit current in the different voltage level of the power grid, andeven excessive. To suppress the short-circuit current in power grid,500kV transformersneutral grounding via small reactance is an effective measure. However, the zero-sequenceparameters of system will be changed. When unsymmetrical earth fault in transmission lineoccurs, the relay protection will be affected. Particularly the main transformer protection andtransmission line protection nearby, they may not act correctly.According to the Guangdong power grid concrete parameter, this paper builds a systemequivalent model in light of autotransformer in500kV substation. When the only oneautotransformer neutral is grounded via small reactance, the effects on power system zero-sequence parameters are analyzed. Meanwhile, a quantitative calculation is accomplishedbased on the relative variation of zero-sequence electric quantities. The following threeInfluencing factors，the unsymmetrical earth fault position variation and the small resistancesize variation and the transmission line length variation, are considered in the calculation.Furthermore, the impacts on protective relaying and coordination between the adjacent linesare analyzed according to curves drawn by Matlab. The zero-sequence current protection of500kV auto-transformer neutral should be re-set to meet sensitivity.On the basis of these studies, this paper puts forward an ring complex power systemequivalent model based on the500kV autotransformer, and uses the actual parameters of theGuangdong Power Grid500kV sites. With and without small reactance of the mainauto-transformer neutral in one substation, a relative variation quantitative calculation ofzero-sequence electric quantities is accomplished when the unsymmetrical earth failurelocation is different. Meanwhile, the superimposed effect of zero-sequence electrical quantities change is researched in different installation circumstances when theautotransformer neutral grounding via small reactance in multiple500kV substation.Furthermore, the effects on protective relaying are analyzed.The zero-sequence currentprotection of the main autotransformer neutral should be re-set to meet sensitivity. Thecorrectness of the theoretical analysis was verified by simulation of an actual large-scaleinterconnected power grid.更多还原