【作者】 高翔；

【导师】 彭敏放； 童嵘；

【作者基本信息】 湖南大学 ， 电气工程（专业学位）， 2019， 硕士

【摘要】 接地网为运行人员安全和电力系统安全运行提供了十分重要的保障。接地网常年经受各种腐蚀,导体截面减小、电气性能下降,成为电力系统的安全隐患。为此,寻找一种不影响系统正常运行的地网腐蚀检测方法,能快速的定位故障,防止事故的扩大;提前预测接地网的剩余寿命,制定检修计划,防止接地事故的发生。本文在分析接地网腐蚀影响因素、腐蚀机理以及接地网现有无损检测方法优缺点的基础上,利用准稳态测量方法实现地网腐蚀状态的检测。应用状态传感器系统模拟地网的腐蚀,分析传感器等效电路模型,应用恒电位阶跃法获取其极化电阻值,利用法拉第定律计算得到接地网在不同环境下的腐蚀深度和腐蚀速率。由于检测现场电磁干扰信号较多且复杂,采用自适应小波滤波算法降低现场干扰因素的影响。通过实例分析证明了该方法是可行的。根据接地网腐蚀速率序列的小样本和非线性特征,分析现有预测算法的优缺点,单一预测模型存在精度不足的问题,以及最小二乘支持向量机对小样本、非线性数据的适用性,提出了基于遗传算法优化的最小二乘支持向量机结合误差校正的预测模型。通过遗传算法优化参数后的LSSVM对腐蚀速率序列进行预测,结合误差预测校正模型来修正预测的结果,降低了极大误差出现的可能性,提高了预测模型的精度和稳定性。在实例分析中验证该模型预测精度更高。本文提出根据类推原理,类比油气管道剩余寿命预测方法,给出了接地网剩余寿命的预测原理、预测模型和具体流程。实现剩余寿命预测的关键在于腐蚀速率预测和地网导体最小允许厚度的确定方法,利用腐蚀速率预测模型实现速率预测,提出利用接地线热稳定性间接确定接地网导体最小厚度的方法。在实例分析中实现了对某220kV变电站接地网的剩余寿命预测,为制定接地网检修计划提供参考。更多还原

【Abstract】 Grounding grid plays an important role in guaranteeing the safety of the operators as well as the safe operation of the power system.But the grounding grid is always subjected to various corrosions,which make the conductor cross section reduced and the electrical performance degraded.All of these make the grounding grid become a safety hazard of the power system.To solve the problems,this paper proposes a grounding corrosion detection method,which won’t affect the normal operation of the system but can quickly locate faults and prevent accidents from expanding.In addition,this paper proposes the method to predict the remaining life of the grounding grid and put forwards the formulate maintenance plans to prevent accidents.By analyzing the influencing factors and mechanisms of grounding grid corrosion and the advantages and disadvantages of existing non-destructive testing methods for grounding grids,this paper proposes a quasi-steady-state measurement method to detect the corrosion state of the grounding grid.The method uses state sensor system to simulate the corrosion of the grounding grid,analyzes the sensor equivalent circuit model,and then uses the constant potential step method to obtain the polarization resistance value.Finally,the Faraday’s law is used to calculate the corrosion depth and corrosion rate of the grounding grid under different environments.In addition,because the on-site electromagnetic interference signal is more and more complex,this method uses adaptive wavelet filtering algorithm to reduce the influence of on-site interference factors.The case study proves the feasibility of the proposed method.Aiming at the problem of insufficient precision of single prediction model,this paper proposes a prediction model based on genetic algorithm optimized least squares support vector machine(LSSVM)combined with error correction.The ground grid corrosion rate sequence data has characteristics of small sample and nonlinear,while the least squares support vector machine has appliability for this type of data.LSSVM is optimized by the genetic algorithm to predict the corrosion rate sequence in this model,and the error prediction correction model can be combined to correct the prediction result,which can reduce the possibility of maximal error and further improve the accuracy and stability of the prediction model.Through comparison and verification in the case study,the model proposed in this paper has higher prediction accuracy.Based on the prediction method of residual life of analog oil and gas pipelines,this paper proposes a prediction method for the remaining life of the grounding grid.The key to achieving residual life prediction is the corrosion rate prediction and the determination of the minimum allowable thickness of the grounding grid conductor.For these two points,this paper uses the corrosion rate prediction model to achieve rate prediction,and indirectly determines the minimum thickness of the grounding grid conductor by using the grounding line thermal stability.In the case analysis,the remaining life prediction of a 220 kV substation grounding grid is realized,which provides a reference for the development of the grounding network maintenance plan.更多还原