【作者】 周怡君；

【导师】 何嘉弘； 陈昊；

【作者基本信息】 东南大学 ， 电气工程（专业学位）， 2024， 硕士

【摘要】 10 kV交联聚乙烯(XLPE)电缆作为城市配电网络中的重要输电设备,其应用范围正在逐步扩大。XLPE电缆在外部电场、温度及机械应力的联合作用下发生劣化,进而因内部放电形成电导率较高的细小树状通道,即为电树枝。电树枝的产生严重威胁着电缆的安全运行。本文研究电缆绝缘内部电树枝的生长机理,建立电树生长、分叉、滞长、击穿的全过程数理模型,通过建立电树能量平衡方程实时判断电树枝的生长状态,同时引入累计损伤变量定量分析电树枝生长过程中绝缘材料的损伤状态,深入探究不同电压等级、不同针板距离下电树枝的生长规律和材料损伤机理,为10 kV电缆绝缘材料的设计以及输电线路的安全稳定运行提供参考。主要研究内容和结果如下:提出了绝缘材料损伤渐变理论作为材料劣化衡量标准。本文将绝缘材料损伤理论的相关思想迁移至绝缘材料中电树区域演化机理分析中,形成绝缘材料损伤渐变理论,建立绝缘材料在受到电树枝损伤之后的损伤渐变模型。通过引入材料损伤变量,量化描述了材料的受损程度,并从机理角度揭示了材料受损与电树发展的耦合关系。基于该模型,本文研究了电树生长的统计性规律和影响因素,提供不同时间下材料整体受损情况的综合评价,为电力电缆绝缘寿命评估提供理论基础和设计依据。提出了电树枝生长判据和电树枝生长能量平衡模型。本文以电树能量平衡模型为基础,揭示10 kV电缆绝缘中电树的随机发展,描述其从起树到击穿或者停止的过程。基于该模型,可以判断电树枝的发展阶段、分叉方向,预测电树在电缆绝缘内部的生长状态,及时更换电缆,减少停电事故的发生。构建了10 kV电缆绝缘内的电树枝生长数理模型。由于电缆在实际运行中容易遇到外部的金属外破和过电压问题,因此仿真模型模拟了在针尖插入为0.6 cm、0.8 cm以及电压等级在10 kV、13 kV、15 kV条件下电树枝的生长全过程,总结了电树枝在不同条件下的生长规律和击穿概率变化。研究发现,针尖插入更深对电树枝的生长起到促进作用,在相同加压时间下,电树枝的生长形态更复杂,对XLPE造成的绝缘破坏更严重,击穿时间缩短,电树枝的生长形态也随针尖插入深度的不同有所变化,0.6 cm为枝状,0.8 cm为松枝状。高压同样对电树枝的生长具有促进作用,在高压下电树枝更容易引发,生长速度更快,也更容易造成击穿,电树枝的生长形态也随电压等级的不同有所变化,10 kV为稀疏枝状,13 kV为密集丛状,15 kV为松枝状。电树枝的击穿概率受到多种因素的影响,随着针板距离的缩短,击穿概率呈指数上升,针尖插入深度为0.8 cm时,击穿概率达到80%,因此在电缆的运行过程中需要注意外部的金属刺破;同时,随着电压等级的升高,松枝状电树枝出现的频率增加,其击穿概率最高,当电压增至15 kV时,击穿概率可达到80%,因此在电缆的运行过程中需要注意电缆的运行电压,避免其长期在超过额定电压的情况下运行。开展了10 kV电缆绝缘内的电树枝生长实验验证。通过开展对仿真模型的实验验证,从电树枝的生长阶段、分形维数、击穿概率3个维度进行对比,生长阶段、分形维数的实验结果和仿真结果的变化趋势一致,击穿概率的误差约为8%,考虑到电树枝生长的随机性以及实验中的某些不可控因素,实验结果和仿真结果的误差均在可接受的范围内,可以验证电树枝随机生长仿真模型的准确性,保证本文提出的绝缘材料损伤理论以及电树能量平衡模型的合理性。更多还原

【Abstract】 As an essential transmission equipment in the urban power distribution network,the 10 kV XLPE cable application scope is gradually expanding.When the XLPE cable deteriorates under the combined action of the external electric field,temperature,and mechanical stress,a small tree-like channel with high conductivity due to internal discharge is formed,called an electric tree.The generation of electric branches seriously threatens the safe operation of cables.The thesis focuses on the growth mechanism of electric branches inside cable insulation.The process of electric tree growth,bifurcation,stagflation,and breakdown is established.In addition,the growth state of electric branches is judged in real-time by establishing the energy balance equation of electric trees.The damage state of insulating materials in the growth process of electric branches is quantitatively analyzed by introducing cumulative damage variables.The growth law and material damage mechanism of electric branches under different voltage levels and pin plate distances are explored to provide a reference for ensuring the safe and stable operation of a 10 kV distribution cable network.The main research contents and results are as follows:The gradual damage theory of insulating materials was proposed as a measure of material deterioration.In this thesis,the relevant ideas of the damage theory of insulating materials are transferred to the analysis of the evolution mechanism of the electric tree region in insulating materials,and the damage gradient theory of insulating materials is formed,and the damage gradient model of insulating materials after being damaged by electric branches is established.By introducing material damage variables,the degree of material damage is quantitatively described,and the coupling relationship between material damage and electron tree development is revealed from the perspective of mechanism.Based on this model,this thesis studies the statistical laws and influencing factors of the growth of electric trees,provides a comprehensive evaluation of the overall damage of materials at different times,and provides a theoretical basis and design basis for the evaluation of the insulation life of power cables.The electric branch growth criterion and the electric branch growth energy balance model were proposed.Based on the energy balance model of the electric tree,this thesis reveals the stochastic development of the electric tree in 10 kV cable insulation,and describes its process from tree initiation to breakdown or stopping.Based on this model,the development stage and bifurcation direction of electric tree branches can be judged,the growth state of electric trees inside the cable insulation can be predicted,and the cables can be replaced in time to reduce the occurrence of power outages.A mathematical model of the growth of electric branches in 10 kV cable insulation was constructed.Due to the fact that the cable is prone to external metal breakage and overvoltage problems in actual operation,the simulation model simulates the whole process of the growth of electric branches under the conditions of 0.6 cm and 0.8 cm of needle tip insertion and voltage levels of 10 kV,13 kV and 15 kV,and summarizes the growth law and breakdown probability changes of electric branches under different conditions.It was found that the deeper insertion of the needle tip promoted the growth of electric branches,and under the same pressurization time,the growth morphology of electric branches was more complex,the insulation damage caused to XLPE was more serious,the breakdown time was shortened,and the growth morphology of electric branches also changed with the depth of needle tip insertion,which was 0.6 cm branch-like and 0.8 cm pine-branched.High voltage also has a promoting effect on the growth of electric branches,under high voltage,electric branches are more likely to trigger,the growth rate is faster,and it is easier to cause breakdown,and the growth form of electric branches also changes with different voltage levels,10 kV is sparse branch,13 kV is dense clumps,and 15 kV is pine branches.The breakdown probability of electric branches is affected by a variety of factors,with the shortening of the distance between the needle plate,the breakdown probability increases exponentially,and the breakdown probability reaches 80%when the needle tip insertion depth is0.8 cm,so it is necessary to pay attention to the external metal puncture during the operation of the cable.At the same time,with the increase of the voltage level,the frequency of pine branch electric tree increases,and its breakdown probability is the highest,when the voltage increases to15 kV,the breakdown probability can reach 80%,so it is necessary to pay attention to the operating voltage of the cable during the operation of the cable to avoid its long-term operation in the case of exceeding the rated voltage.The experimental verification of the growth of electric branches in the insulation of 10 kV cable was carried out.Through the experimental verification of the simulation model,the experimental results of the growth stage,fractal dimension and breakdown probability of electric tree branches are compared,the change trend of the experimental results of growth stage and fractal dimension is consistent with the simulation results,and the error of the breakdown probability is about 8%,considering the randomness of the growth of electric tree branches and some uncontrollable factors in the experiment,the errors of the experimental results and the simulation results are within the acceptable range,and the accuracy of the simulation model of random growth of electric tree branches can be verified.The rationality of the insulating material damage theory and the electric tree energy balance model proposed in this paper is ensured.更多还原