【作者】 邓江；

【导师】 杨雁；

【作者基本信息】 西南交通大学 ， 电气工程（专业学位）， 2020， 硕士

【摘要】 高压直流输电换流站中,换流变压器阀侧套管和直流穿墙套管作为连接换流站阀厅与交流场、直流场设备的关键部件,是同时承载系统全电压和全电流的关键电气连接设备。干式SF₆气体绝缘高压直流套管为当前主流复合绝缘结构的直流套管,在我国特高压直流输电工程中得到广泛应用。当该类型套管内绝缘结构设计不合理时,即便通过了国际标准规定试验的进口性能优良产品,也会在长期运行过程中暴露设计缺陷,从而引发套管故障。因此本文以干式SF₆气体绝缘特高压直流套管的电热场分布特性研究为基础,将直流套管的电-热耦合有限元计算与传统内绝缘结构设计方法进行结合,提出内绝缘优化策略并对传统电容芯体设计方法进行优化。本文研究对我国直流工程的建设和干式SF₆气体绝缘特高压直流套管的国产化有一定指导意义和参考价值。本文首先通过交直流电场计算理论与运行工况下直流套管的电压、电流的波形分析,提出了换流变阀侧套管和直流穿墙套管各自不同的电场计算方法和热损耗计算方法:换流变阀侧套管的电场计算,应分别计算直流电压下套管本体恒定电流场与气体域静电场的耦合场,和各次谐波下套管的静电场并将其叠加;热损耗计算需考虑导电管的欧姆损耗以及电容芯体的欧姆损耗和介质损耗,导电管的欧姆损耗计算需考虑趋肤效应。直流穿墙套管的电场计算,仅需进行套管本体恒定电流场与气体域静电场的计算;热损耗计算需考虑导电管的欧姆损耗以及电容芯体的欧姆损耗。并介绍了套管温度场的计算方法。然后介绍了传统电容芯体的设计原理与设计方法,对比了传统电容芯体设计方法的优劣,并根据仿真结果与理论计算值的对比,证明了本文电场仿真计算方法的正确性。依据±400k V干式SF₆气体绝缘直流穿墙套管图纸,建立了有限元仿真模型,根据温度场仿真结果与温升试验测量数据的对比,证明了温度场仿真方法的正确性。分析了直流电压下电容芯体电场强度的影响因素,提出了材料优化选型、减小导电管载流密度和温度梯度下内绝缘结构电-热耦合设计的优化策略。最后基于本文所提出的电-热耦合内绝缘优化设计方法,依据特高压直流工程中对两种套管的技术参数要求,分别设计了±400k V直流穿墙套管和±1100k V换流变阀侧套管,并对两支套管进行各试验电压以及运行工况下电热场分布特性分析,对优化设计方法进行评估。计算结果表明设计的干式SF₆气体绝缘直流套管,各试验电压下满足工程中场强控制要求,实际运行工况下轴向和径向电场能相对均匀分布,绝缘结构设计合理。更多还原

【Abstract】 In the High Voltage Direct Current（HVDC）transmission converter station,the valve side bushing of the converter transformer（valve side bushing）and the DC wall bushing are the key components connecting the valve hall of the converter station and the AC field and DC field equipment.It is a key electrical connection device that carries the full voltage and full current of the system at the same time.Dry-type SF₆ gas-insulated HVDC bushing is the main type of DC bushing in converter stations.Dry-type SF₆ gas-insulated high-voltage DC bushing is the current mainstream DC bushing with composite insulation structure,which is widely used in Ultra High Voltage Direct Current（UHVDC）transmission projects in China.When the design of the insulation structure in this type of bushing is unreasonable,even the bushings that pass the standard assessment test will be exposed to defects during long-term operation,which ultimately leads to the failure of the overall bushing insulation.Therefore,this paper based on the study of the electric and thermal field distribution characteristics of the dry-type SF₆ gas-insulated HVDC bushing,the electric-thermal coupling finite element calculation of the DC bushing is combined with the traditional internal insulation structure design method to optimize the traditional condenser body design method.This study has certain guiding significance and reference value for the construction of DC projects in China and the localization of dry-type SF6 gas insulated UHVDC bushings.In this paper,first,through the calculation theory of AC and DC electric fields and the waveform analysis of the voltage and current of the DC bushing under operating conditions,different electric field calculation methods and heat loss calculation methods for the valve side bushing and DC wall bushing are proposed.For the calculation of the electric field of valve side bushing,the coupling field of the constant current field of the bushing body under the DC voltage and the electrostatic field of the gas domain,and the electrostatic field of the bushing under each harmonic should be calculated and superimposed;the heat loss calculation of valve side bushing needs to consider the ohmic loss of the conductive tube and the ohmic loss and dielectric loss of the condenser body,and the skin effect should be considered in the calculation of the ohmic loss of the conductive tube.The calculation of the electric field of the DC wall bushing only requires the calculation of the constant current field of the bushing body and the electrostatic field of the gas domain;the heat loss calculation needs to consider the ohmic loss of the conductive tube and the ohmic loss of the condenser body.And the calculation method of bushing temperature field is introduced.Then the design principle and design method of the traditional condenser body is introduced,the advantages and disadvantages of the traditional condenser body design method is compared,and the correctness of the electric field simulation calculation method in this paper according to the comparison between the simulation result and the theoretical calculation value is proved.According to the drawing of±400k V dry-type SF₆ gas-insulated DC wall bushing,a finite element simulation model is established.The comparison between the temperature field simulation results and the temperature rise test measurement data proves the correctness of the temperature field simulation method,making it compatible with the electric field simulation coupling can objectively reflect the limitations of traditional condenser body design methods at high currents.The influencing factors of the electric field strength of the condenser body under DC voltage are analyzed,and optimization strategies for optimizing the material properties,reducing the current carrying density of the conductive tube and the electrical-thermal coupling design of the inner insulation structure are proposed.Finally,based on the electric-thermal coupling internal insulation optimization design method proposed in this paper,according to the technical parameters of two types of bushings in the UHVDC project,±400k V UHVDC wall bushings and±1100k V UHVDC valve side bushing are designed respectively,the distribution characteristics of the electric heating field under the test voltage and operating conditions of the two bushings are analyzed,the optimal design method is evaluated.The calculation results show that the designed dry-type SF₆ gas-insulated DC bushing meets the field strength control requirements under various types of test voltages,and the axial and radial electric fields can be relatively evenly distributed under actual operating conditions,and the insulation design is reasonable.更多还原