Insulating Materials

To study the influence of extrusion temperature on the mesoscopic morphology and comprehensive properties of high-voltage cable insulation masterbatch, and analyze its mechanism, insulating materials with different mesoscopic micro-morphologies were prepared by controlling the extrusion temperature of the insulating material. Then, combined with the microscopic characterization of the system, comprehensive electrical and mechanical performance testing, and simulation methods, the reasons for the performance differences of insulating materials are revealed and the mechanism is verified and analyzed. The results showed that at an extrusion temperature of 120 ℃, the insulation material could be fully plasticized without excessive melting, and the crystallinity and crystal size of the insulation material reached the optimal values of 42.28

In order to obtain the location information of defects in buffer layer of HV cable,at first,according to the surface morphological characteristics of buffer layer,the buffer layer states were devided into dry state,damp state,corroded state,and corroded-ablative state,and the change law of volume resistivity and relative dielectric constant during the development of defects from dry state to corroded-ablative state of buffer layer was studied via thin slice samples.Then the computing formula of the distributed capacitance and distributed conductance in the network of HV cables transmission line was derived.The feasibility of applying the FDR method to locate defects in the buffer layer of HV cables was also evaluated.Finally,a long cable experimental platform was built in the laboratory to study the effectiveness of the FDR method in locating buffer layer defects.The results show that the development of buffer layer defect mainly affects the distributed capacitance,and impedance discontinuity points generate in the process.FDR can locate the moisture and defects of the buffer layer,but the further distinction between corrosion defects and ablation defects needs to be combined with other state detection methods.

In response to the problem of uneven distribution of electric field and severe local electric field distortion in insulation partitions in high-voltage switchgear, functional material technology is introduced into the preparation of insulation partitions. Two optimization methods, internal insulation structure optimization and surface insulation structure optimization, are proposed. Based on the optimization method, a geometric model of the insulation partition is established. By changing the upper limit of the material’s dielectric constant Electric field and temperature field simulation calculations were conducted on parameters such as insulation partition thickness and surface coating thickness, and their effects on the optimization of electric field distribution were analyzed and compared. The research results indicate that compared to traditional homogeneous insulation partitions, changing the internal insulation structure and adding surface coatings can reduce the maximum field strength along the surface. When the thickness of the insulation partition increases to 12 mm, the effect is optimal, and the maximum field strength along the surface can be reduced by 69.8%; When the surface coating thickness is 1.5 mm, the effect is optimal, and the maximum field strength along the surface can be reduced by 68.5%. Finally, a comparison was made between the two optimization methods, and the differences in the effectiveness of regulating the electric field between the two were analyzed.

Aiming at the problems of large specific surface area of conventional flake boron nitride and sharp increase in resin viscosity when compounded with epoxy resin,we prepared spherical boron nitride and used it as a filler to compound with epoxy resin to prepare spherical boron nitride/epoxy composites.The preparation process and curing characteristics of spherical boron nitride/epoxy composites were studied,and the influences of the morphology and filling amount of flake/spherical boron nitride fillers on the mechanical and electrical properties of epoxy resin composites were compared.The results show that with the increase of reaction temperature,the curing degree change curve of epoxy resin shows"S"shape,and the curing process can be roughly divided into three stages of"slow-fast-slow".In terms of mechanical properties,adding a small amount of boron nitride can improve the mechanical properties of the epoxy resin composites;when the filling amount is high,spherical boron nitride/epoxy composites have better mechanical properties than flake boron nitride/epoxy composites.In terms of electrical properties,the relative dielectric constant of the epoxy resin composites increases with the increase of boron nitride content,and the dielectric loss factor is lower than 0.02;compared with the flake boron nitride/epoxy composites,the spherical boron nitride/epoxy composites have less"filler-resin"interface,lower relative dielectric constant and dielectric loss factor;adding an appropriate amount of boron nitride can significantly improve the volume resistivity and electric strength of composites.

本文综述了目前丙烯基电缆研发中的聚丙烯改性手段、电缆研发及投运情况以及聚丙烯电缆相关的规程规范,根据聚丙烯电缆研发现状,总结了聚丙烯电缆将来运行中可能遇到的问题并提出研究建议,为聚丙烯电缆后续的研究与商业应用提供参考.

为研究变压器油中添加抗氧化剂对绝缘纸热老化性能的影响,向环烷基矿物油、绝缘纸组成的绝缘体系中分别添加T501、T531、DBP 3种抗氧化剂,抗氧化剂质量分数均为0.4%,在130℃下进行热老化试验,老化时长为600 h.每隔120 h测定绝缘油中水分含量和糠醛含量、绝缘纸中水分含量与聚合度,同时对老化绝缘纸进行FTIR、XRD、SEM、EDS表征.结果表明:添加抗氧化剂T501、T531对绝缘纸的劣化影响较小,添加抗氧化剂DBP的油中绝缘纸在老化后期劣化程度加剧;由于T531抗氧化剂具有中和、水解双重作用,对纤维素的降解起到抑制作用,T531绝缘纸的老化程度最轻.

C6F12O是一种具有潜力的SF6替代气体,为了探究C6F12O/CO2混合气体在悬浮电极缺陷不同局部放电强度下的分解特性,搭建了局部放电分解实验平台,在不同外施电压下对C6F12O/CO2混合气体进行96 h局部放电分解实验,利用气相色谱法对分解组分进行定量分析,对分解组分含量、产气速率、特征气体比值与局部放电强度的关系分别进行了研究.结果表明:4种典型产物(CF4、C2F6、C3F8、C3F7H)浓度、产气速率的变化规律上存在差异,可选择作为判断局部放电强度的特征组分;特征组分浓度关系为c(CF4)>c(C2F6)≈c(C3F8)>c(C3F7H),产气速率关系与之相类似;特征组分浓度随放电强度增加呈"线性-饱和"的增长关系;初步认为可以利用c(CF4)/c(C3F7H)作为辅助依据,c(CF4+C2F6+ C3F8)2/c(C3F7H)2作为主要依据,结合组分浓度以及产气速率,可以进一步判断PD强度和缺陷严重程度,研究结果为找出适用于C6F12O/CO2混合气体绝缘设备的运维监测手段提供了参考.

硅橡胶复合绝缘子在湿热地区中运行其表面存在霉菌附着引起的微生物染污问题,霉菌作为一种特殊的生物污秽对硅橡胶绝缘子性能的影响尚不明确.本文对悬式绝缘子串进行霉菌染污,并在不同污秽等级下对绝缘子串沿面闪络特性进行分析,通过憎水性分析、扫描电镜以及红外光谱3种微观测试方法研究霉菌浓度对绝缘子沿面闪络特性的影响.结果表明:对于同一污秽等级的绝缘子,当存在霉菌污染时,相较于无霉菌染污的绝缘子,霉菌对硅橡胶表面结构造成破坏,导致硅橡胶憎水性显著降低,进而造成闪络电压大幅降低,与对照组相比,沿面闪络电压最低可下降至原始水平的76%;但在同一污秽等级下,霉菌浓度达到107 个/cm2时,沿面闪络电压下降出现拐点,下降速度放缓并趋于饱和状态.综上,霉菌的附着行为与硅橡胶自然老化协同作用使霉菌菌丝在绝缘子表面形成微型孔洞,导致有机硅橡胶分子链断裂,降低了绝缘子的闪络电压,影响了硅橡胶绝缘子的稳定运行.

为开发一种能实时掌握电缆绝缘状态的监测技术,本文通过模拟XLPE电缆绝缘中出现金属尖刺缺陷,对其阻性电流的谐波成分进行分析,从理论和实验两方面为实现基于阻性电流谐波成分的电缆绝缘诊断提供支撑.首先,基于聚合物的跳跃电导模型,对XLPE的电导特性进行了仿真与理论分析.而后建立了XLPE金属尖刺缺陷仿真模型,对不同针尖曲率半径以及针板间距下阻性电流密度的谐波成分进行了仿真分析.最后制作了3种不同规格的XLPE金属尖刺缺陷试样,在针尖曲率半径为30 μm、针板间距为2 mm,针尖曲率半径为90 μm、针板间距为3 mm以及针尖曲率半径为30 μm、针板间距为3 mm条件下进行了验证实验.结果表明:当XLPE绝缘中存在导体尖刺缺陷时,由于局部电场强度的急剧增大,导致绝缘材料的电导特性随着交流电压波形的变化而在欧姆区与非欧姆区之间反复,使得阻性电流的波形发生畸变,叠加了高次谐波分量;当XLPE绝缘中存在导体尖刺缺陷时,其阻性电流中会存在明显的3次与5次谐波分量,二者构成了阻性电流谐波分量的主要组成部分;随着导体尖刺缺陷的严重程度增加,阻性电流的谐波畸变率以及电导率畸变率均有明显的上升,可以谐波畸变率作为判断缺陷严重程度的特征量.

本文制备了热致变色微胶囊环氧树脂复合绝缘材料(TEP),并对其工频介电常数(εr)、介质损耗因数(tanδ)以及直流电导率(σ)的温度特性进行分析.结果表明:复合绝缘材料介电常数的温度特性在70℃时存在拐点,当温度低于70℃时,εr随温度升高迅速增大;当温度高于70℃时,εr随温度的变化率显著下降.tanδ在温度为50～70℃内显著降低.而添加热致变色微胶囊可以有效降低复合绝缘材料的直流电导率.在热致变色温度区间50～70℃内,热致变色微胶囊内部会发生固液相变,这是导致εr和tanδ特殊温度特性的主要原因.在固液相变过程中,微胶囊内芯材的分子活性逐渐增强,使其随外电场转向极化所需克服的阻力减小,导致εr随温度升高迅速增大、tanδ显著降低.当微胶囊内芯材全部转变为液态后,其分子活性随温度变化程度减小,导致εr随温度的变化显著降低.

本文采用分子动力学模拟的方法建立了两种硅烷偶联剂(KH570、KH792)改性前后TiO2/植物绝缘油界面结构的纳米分子模型,并进一步通过动力学仿真研究了硅烷偶联剂改性前后TiO2界面对油中水分子扩散行为的影响.结果表明:相较于未处理的TiO2,改性后TiO2界面对水分子有更强的吸附性,束缚了水分子在油中的扩散行为,致使其扩散系数显著降低,从而降低了油中水分子杂质形成"小桥"的概率,提升了植物绝缘油的绝缘性能,其中KH792的改性效果更为显著.进一步通过计算水分子与TiO2界面体系相互作用能、形成氢键的数量和自由体积分数,解释了上述现象的成因与物理机制,为研究纳米粒子掺杂改善植物绝缘油绝缘性能提供了理论支撑.

为了研究黑色页岩作为填料应用于塑料工业的可能性,本文对桂林地区的黑色页岩进行了成分和形貌研究,发现其为纳米层状结构,主要由二氧化硅、钾长石及有机碳组成.利用不同的偶联剂与表面活性剂改性黑色页岩,制备了黑色页岩/HDPE复合材料,并对其力学性能、形貌、体积电阻率和介电常数进行了研究.结果表明:铝酸酯偶联剂与十二烷基苯磺酸钠能够改善页岩与HDPE之间的相容性,当页岩填充量为50份时,黑色页岩/HDPE复合材料的拉伸强度、冲击强度和体积电阻率有所降低,拉伸强度仍保持在23.47 MPa,冲击强度最高为6.39 kJ/m2,体积电阻率也可维持在1014 Ω·cm以上,保持了较好的力学性能和绝缘性能.

为了研究潮湿环境对牵引电机定子绝缘性能的影响,本文以牵引电机新造定子绕组和检修定子绕组绝缘系统为研究对象,对绕组及其端部分别进行了湿热试验,测试了绕组绝缘系统吸潮前后绝缘性能的变化,分析了湿气向绝缘系统渗透的主要途径.结果表明:定子绕组绝缘系统受潮后会使其绝缘电阻下降,潮湿环境下最薄弱部分为端部联线焊接绝缘,是湿气向绝缘系统渗透的主要途径,该湿气通道一旦形成湿气容易被烘干,但在潮湿环境下湿气又会进入通道使绝缘电阻下降,长期运行后潮湿会导致定子绕组的绝缘性能下降.

海底电缆在运输、敷设过程中,不可避免地会发生扭转,若扭转角度过大,会对其造成不可恢复的损伤.本文利用有限元方法建立了海底电缆的扭转模型,通过分析应力、应变的时空分布特点,确定了能够有效反映海缆力学特性的特征参量,制定了扭转故障发生时各特征参量的阈值,建立了能够表征海底电缆扭转行为的力学参量体系.结果表明:海缆发生扭转初期,其轴向各结构应力分布较为均匀;随着扭转角度的增加,缆体轴向应力分布会出现波动,可建立包括铜导体应力、XLPE绝缘层应力、铅合金护套应力、铠装层应力和扭转角度的参量体系,对海缆扭转行为进行参量化评价.

绝缘纸的性能决定了电力变压器的可靠性和寿命,为了保障变压器安全可靠运行,本文结合国内外文献及相关研究成果,从纳米粒子改性和热稳定剂改性阐述当前采用物理改性技术提升绝缘纸性能的研究现状,分析两种改性方式的利弊,探究经济可行的电力变压器用纤维素绝缘纸改性方法,从本质上提升变压器运行可靠性.

为了指导防污闪涂料开发中常温固化氟碳类树脂成膜物的选型,采用FT-IR、AFM、紫外老化、热重分析、接触角测试、体积电阻率和高压电容电桥对其结构和性能进行表征.结果表明:FEVE基I型和Ⅱ型氟碳树脂固化剂的最佳质量分数分别为19%和24%.在最佳固化剂含量下,FEVE基I型和Ⅱ型氟碳树脂的接触角分别为91°和104°.经800 h紫外老化后,氟碳树脂的外观颜色、憎水性、硬度、附着力、热分解温度及分子结构均未发生变化.经过30 min的超声雾润湿后,氟碳树脂的交流湿闪电压在25 kV左右,说明FEVE基氟碳树脂具有优异的电气绝缘性能和耐老化性能,是良好的防污闪涂料开发用基料.

为解决电力电缆与其终端绝缘电场分布不均匀,易造成界面击穿及沿面放电的问题,本文对35 kV冷缩式电力电缆终端结构参数进行优化以提高其绝缘水平.首先基于COMSOL仿真软件分析应力锥的轴向长度和端部半径对终端电场分布的影响,得出终端结构参数的最优组合;随后研制电力电缆终端样品,通过工频交流耐压、局部放电试验进行性能指标的对比验证.结果表明:电力电缆终端应力锥的轴向长度是影响其界面电场变化与分布的主要因素,端部半径的变化对终端电场的影响较小;应力锥轴向长度的增大缓解了界面电场强度,但容易引发沿面放电问题;应力锥的轴向长度及端部半径最优值分别为25 mm和2.5 mm.

本文利用COMSOL计算和分析了半导电层电性参数对站用支柱绝缘子表面电场分布的影响.结果表明:半导电层对潮湿生成的水珠、湿污和干污引起的最大电场均有不同程度的削弱作用,湿污最为显著,电场降幅为41.58%;在高压端涂覆半导电层对电场的改善效果显著,与不涂覆半导电层相比,表面最大电场最大降幅为14.5%;高、低压端涂覆各自最佳相对介电常数的半导电层,其电场改善的综合均衡性较好;在正常瓷件电性参数范围内,半导电层最佳电性参数具有通用性,高压端最佳半导电层相对介电常数为22,低压端最佳半导电层相对介电常数为12,此外,高、低压端半导电层的电阻率至少分别大于1×107 Ω·m和6×107 Ω·m,其最大电场才将小于不涂覆半导电层的情况.

研究水轮发电机定子线棒在高温和局部放电作用下的产气规律,可以为基于分解气体法的水轮发电机绝缘老化状态监测提供依据.针对水电站实际使用的定子线棒,搭建了高温热解实验平台,对100、120、150、250℃下的定子线棒热解气体进行了研究;搭建了定子线棒局部放电实验平台,对定子线棒局部放电下的臭氧生成规律进行了研究.结果表明:CO和CO2适合作为定子线棒高温故障的早期特征气体;当定子线棒表面发生局部放电时,臭氧浓度与放电电压和放电时间有相关性;在同样放电条件下,半导电硅胶产生的臭氧浓度生成速率更大,具有更强的抗电晕性能,在定子槽中填充半导电硅胶有利于定子线棒的安全运行和在线监测.

本文介绍了变压器匝间击穿特性与研究方法、匝间故障的检测与保护及其特性,并对变压器匝间故障的研究方向进行了展望,可为变压器匝间故障的学术研究与运行维护提供参考.