【作者】 金鑫；

【导师】 薛永端；

【作者基本信息】 中国石油大学(华东) ， 电气工程， 2020， 硕士

【摘要】 为了使多数接地故障自动熄弧并快速可靠切除永久故障,减小接地故障对配电网的影响,国内部分供电企业提出配电网中性点可采用灵活接地方式(消弧线圈并联小电阻接地方式),已在多地试运行。然而,目前针对灵活接地方式的研究大多集中于装置研发与接地方式改造等问题,而对其发生单相接地时的故障特征缺乏系统性、全局性的理论分析,现有接地保护大多直接沿用小电阻接地系统常用的定时限零序过电流保护,仍存在高阻接地时保护灵敏度不足以及故障信息利用不充分等问题。首先,建立了灵活接地系统单相接地故障零序等值模型,分析了灵活接地系统单相接地故障时并联小电阻投入前及投入后全过程的零序电压、各电气节点处零序电流的幅值、相位特征及其在并联小电阻投入前后的变化特征,为灵活接地方式下现有接地保护的适应性分析及新型接地保护研究提供理论依据。其次,根据灵活接地系统的特性,提出灵活接地方式对接地保护的要求,在灵活接地系统单相接地故障全过程特征分析的基础上,对现有配电网接地保护方法,包括:定时限零序过电流保护、零序功率方向保护、反时限零序电流保护、电压制动式零序电流保护、零序电流比较式保护、时域波形畸变式保护以及零序电流突变式保护在灵活接地方式下的适应性进行分析,并给出定值修正原则和改进方法。进一步地,分析总结了灵活接地系统单相接地故障全过程故障点上游及下游检测点处零序测量导纳特征,发现:并联小电阻投入前故障点上游及下游零序测量导纳模值均较小,并联小电阻投入后故障点上游零序测量导纳模值大幅增加,而故障点下游零序测量导纳模值不变。据此提出了基于零序导纳变化的接地故障方向算法。在零序测量导纳特征分析的基础上,分析故障点上游及下游检测点处电压-电流分布特征,提出了基于电压-电流分区的接地故障方向算法,反映过渡电阻能力最大可达3000Ω。同时,给出了基于上述接地故障方向算法的多级保护及馈线自动化方案。最后,利用Matlab-Simulink数字仿真和现场人工接地试验数据,验证了本文分析所得结论的正确性及所提两种接地故障方向算法的有效性。更多还原

【Abstract】 In order to make most of the earth faults automatically extinguish the arc and remove the permanent faults quickly and reliably,and reduce the influence of the earth faults on the distribution network,some domestic power supply enterprises put forward that the neutral point of the distribution network can be flexibly grounded(arc suppression coil in parallel with small resistance grounding mode),which has been in multi ground trial operation.However,at present,most of the researches on flexible grounding methods are focused on solving the problems existing in the practical application process,while the theoretical analysis on the fault characteristics of single-phase grounding is lack of systematic and global.Most of the existing ground protection directly uses the fixed time zero sequence over-current protection commonly used in the small resistance grounding system,but there are still some problems such as insufficient sensitivity of protection and insufficient utilization of fault information in the case of high resistance grounding.First of all,the zero sequence equivalent model of single-phase ground fault in flexible grounding system is established,and the zero sequence voltage before and after the input of parallel resistance,the amplitude and phase characteristics of zero sequence current at each electrical node and the change characteristics before and after the input of parallel resistance are analyzed.It can provide theoretical basis for the adaptability analysis of the flexible grounding mode and the research of the new grounding protection.Secondly,according to the characteristics of flexible grounding system,the requirements of flexible grounding mode for grounding protection are proposed.Based on the analysis of the whole process characteristics of single-phase ground fault in flexible grounding system,this paper analyzes the adaptability of the existing grounding protection methods in flexible grounding mode.It includes definite time zero sequence overcurrent protection,zero sequence power direction protection,inverse time zero sequence current protection,voltage braking zero sequence current protection,zero sequence current comparison protection,time domain waveform distortion protection and zero sequence current mutation protection.The principle and method of fixed value correction are given.Furthermore,the zero sequence measurement admittance characteristics at the upstream and downstream detection points of single-phase ground fault in flexible grounding system are analyzed and summarized.It is found that the admittance modes of zero sequence measurement upstream and downstream of the fault point are small before the parallel resistance is put into operation,and the admittance modes of zero sequence measurement upstream of the fault point increase significantly after the parallel resistance is put into operation,while the admittance modes of zero sequence measurement downstream of the fault point remain unchanged.Based on this,an algorithm of ground fault direction based on the change of zero sequence admittance is proposed.Secondly,based on the analysis of admittance characteristics of zero sequence measurement.Then,the distribution characteristics of voltage and current at the upstream and downstream detection points of fault point are analyzed,and a fault direction algorithm based on voltage current partition is proposed.The maximum capacity of transition resistance can reach 3000 Ω.The scheme of multi-level protection and feeder automation based on the above algorithm is given.Finally,the correctness of the conclusions and the effectiveness of the two algorithms are verified by using MATLAB-Simulink digital simulation and field artificial grounding test data.更多还原