Resistance Measurements and Interpretations Relating to Flashover of Artificially Contaminated Ceramic Insulator Strings

The flashover of insulator strings occurring at normal working voltages undercontaminated/polluted conditions, obviously deserves serious consideration. Though much researchhas been gone into pollution-induced flashover phenomena but grey areas still exist in ourknowledge. In the present experimental study the breakdown (flashover) voltages across gaps oninsulator top surfaces and gaps between sheds (on the underside of an insulator), also the flashoverstudies on a single unit and a 3-unit insulator strings were carried out. An attempt has been madeto correlate the values obtained for all the cases. From the present investigation it was found thatresistance measurement of individual units of a polluted 3-unit string before and after flashoverindicates that strongly differing resistances could be the cause of flashover of ceramic discinsulator strings.

Study of Temperature Distribution Along an Artificially Polluted Insulator String

Insulator becomes wet partially or completely, and the pollution layer on itbecomes conductive, when collecting pollutants for an extended period during dew, light rain, mist,fog or snow melting. Heavy rain is a complicated factor that it may wash away the pollution layerwithout initiating other stages of breakdown or it may bridge the gaps between sheds to promoteflashover. The insulator with a conducting pollution layer being energized, can cause a surfaceleakage current to flow (also temperature-rise). As the surface conductivity is non-uniform, theconducting pollution layer becomes broken by dry bands (at spots of high current density),interrupting the flow of leakage current. Voltage across insulator gets concentrated across drybands, and causes high electric stress and breakdown (dry band arcing). If the resistance of theinsulator surface is sufficiently low, the dry band arcs can be propagated to bridge the terminalscausing flashover. The present paper concerns the evaluation of the temperature distribution alongthe surface of an energized artificially polluted insulator string.

Laboratory test on the combined cooling effect of L-shaped thermosyphons and thermal insulation on high-grade roadway construction in permafrost regions

With the completion of the Qinghai-Tibetan Railway,economic development of related areas has been greatly accelerated.This,in return,calls for building or upgrading more roadways,especially high-grade roadways.In cold regions,the thawing of permafrost can induce settlement damage of and even failure to railway (or roadway) embankments.Thermosyphons (self-powered refrigera-tion devices that are used to help keep the permafrost cool) have proved effective in mitigating thaw settlement by maintaining the thermal stability of the embankments.However,for high-grade roadway embankments of great width,stabilizing or cooling ef-fects of traditional geotechnological measures may be limited.To enhance the cooling effect of thermosyphons,an L-shaped thermosyphon was designed.A laboratory test was carried out to study the combined cooling effect of the L-shaped thermosyphon and thermal insulation applying to roadbed construction.The angle between the evaporator and condenser sections of the L-shaped thermosyphon is 134 degrees,and the L-shaped thermosyphon was inserted into the soil at an angle of 5 degrees with the road surface.The tested results show that the L-shaped thermosyphon is effective in removing heat from a roadway in winter.When the ambient air temperature is lower than the soil temperature,the thermosyphon is active and extracts the heat in the soil around it.When the ambient air temperature is higher than the soil temperature,the thermosyphon is inactive,and no heat is in-jected into the soil through the L-shaped thermosyphon.Compared to embankments with straight thermosyphons,the inner parts of the embankments with L-shaped thermosyphons were significantly cooled.It is hoped that the present study would be useful to the application of L-shaped thermosyphons in the construction of high-grade roadways in cold regions.

Shaped Insulating Refractory Product—High Alumina Bricks

1 Scope This standard specifies the classification, shape and dimension, technical requirements, test methods, quality appraisal procedure, packing, marking, transportation, storage, and quality certificate of high alumina insulating bricks.

Shaped Insulating Refractory Products——Determination of Cold Crushing Strength

1 Scope This standard specifies a method for determination of the cold crushing strength of shaped insulating refractory products.

Shaped Insulating Refractory Products——Determination of Permanent Linear Change on Heating

1 Scope This standard covers the definition, technical requirement, apparatus, specimen, test procedure, calculation and test report on permanent linear change of shaped insulating refractory products.

Shaped Insulating Refractory Products——Determination of Bulk Density and True Porosity

1 Scope This standard specifies a method for the determination of the bulk density and true porosity of shaped insulating refractory products.

Use of Artificial Neural Networks for Location of Defective Insulators in Power Lines

This is an extended version of the same titled paper presented at the 21st CIRED. It discusses a new technique for identification and location of defective insulator strings in power lines based on the analysis of high frequency signals generated by corona effect. Damaged insulator strings may lead to loss of insulation and hence to the corona effect, in other words, to partial discharges. These partial discharges can be detected by a system composed of a capacitive coupling device （region between the phase and the metal body of a current transformer）, a data acquisition board and a computer. Analyzing the waveform of these partial discharges through a neural network based software, it is possible to identify and locate the defective insulator string. This paper discusses how this software analysis works and why its technique is suitable for this application. Hence the results of key tests performed along the development are discussed, pointing out the main factors that affect their performance.

500 kV双联耐张瓷绝缘子串的串间放电现象

以某换流站500 kV出线双联耐张瓷绝缘子串为研究对象,研究了双联瓷绝缘子串串间放电现象的成因。开展了电阻测试、剖面染色等实验,建立了双联瓷绝缘子串电场与放电仿真模型,获得了双联绝缘子串空间电场分布规律。研究结果表明:水汽侵入水泥黏合剂缝隙导致多个绝缘子阻值下降形成大量零值绝缘子(西侧20片、东侧4片)。由于两侧零值绝缘子数量差距较大,产生122 kV串间电位差是串间放电的主要成因。

卷吸限制与火焰融合对U型外立面保温材料火蔓延的影响

本文从火蔓延速率、温度及热流3个方面,研究了U型结构侧向和底部空气卷吸限制以及火焰相互作用对U型结构外立面保温材料顺流火蔓延行为特性的影响.研究发现:侧向空气卷吸限制增大了火蔓延速率、温升和热流;底部空气卷吸限制整体上减小了火蔓延速率、增大了温升和热流;背墙火焰与边墙火焰的相互作用增大了火蔓延速率、温升和热流.

基于多视投影的电力杆塔点云绝缘子串快速提取

在无人机自动巡检中,需要根据电力走廊带点云中绝缘子串的位置进行航线规划。由于电力走廊带长度跨越较大,杆塔数量众多,人工进行绝缘子串位置标注的工作量巨大。同时点云数据散乱无序,在三维空间中直接定位绝缘子串耗时长。为此,本文提出多视二维投影,快速提取三维杆塔点云中的绝缘子串。该方法首先利用鲁棒主成分分析,在俯视图中分析杆塔顶端横担水平方向,统一杆塔点云的朝向。接着,在侧视图中通过霍夫直线检测,对电力线高度进行快速定位,并根据电力线与横担的空间关系,将相应的绝缘子串分为顶层悬挂、竖直绝缘子串与水平绝缘子串三类。最后,在多视投影中进行角点检测,对绝缘子串与电力线、杆塔的连接端点进行定位,实现快速的绝缘子串提取。本文提出的方法在50 km的电力走廊带中的97座不同类型杆塔的867个绝缘子串上进行了提取实验,证明了该方法能对不同类型绝缘子串进行快速提取。

新型密柱支撑张弦铝合金结构设计与施工关键技术研究

世博温室项目屋盖为任意不规则曲线组成的无曲率平面,采用异形多边形网格加大透光率,基于这些特点,选型最终定为张弦铝合金网格结构。本项目挤压出新型“日”字型挤压铝合金构件以更好地承受屋盖面内弯矩,保证杆件与整体结构平面内有效传力。设计了新型刚接板式节点并通过足尺试验和精细化有限元分析研究了节点刚度与极限承载力,试验及有限元对比分析结果表明,该类节点有较高的抗剪、平面内和平面外承载力。阐述了弯扭构件数字化加工工艺及不规则铝合金特殊单元式的装配式预拼装技术,引入立面幕墙与主体结构一体化设计技术,其中立面幕墙面板设计首次通过整体协同分析考虑了主体结构变形的影响,计算结果表明设计构造满足要求。重点说明了双向正交布置拉索的施工张拉模拟计算方法,验证了索力分级张拉时结构处于安全状态,张拉完毕结构变形满足要求。

特高压直流输电线路直线塔V型悬垂绝缘子串选型

在特高压直流输电线路工程中,直线塔通常采用导线V型悬垂绝缘子串,由于该金具串形式多样,受力复杂,在选型时往往又存在粗放设计的情况,因此会使工程存在一定的资源浪费情况。文章利用受力平衡原理对直线塔V型悬垂绝缘子串选型的数学模型进行分析,得到V型悬垂绝缘子串选型计算方法,给出计算程序编写流程图,将程序应用于某±800 kV特高压直流输电线路工程中,验证了该方法的正确性和可行性。

基于风偏角限制的防风偏绝缘子串应用研究

为解决输电线路悬垂绝缘子串风偏造成空气间隙不足的问题,提出一种将导线与塔材空气间隙限制在操作过电压间隙范围以外的复合绝缘子串封挡装配方法,并对绝缘子串封挡和挂点杆件受力进行了分析计算。以110~500kV电压等级输电线路为例,从导线水平风荷载入手,基于故障风速数据确定复合绝缘子串承受冲击荷载范围;分析导线发生摇摆时复合绝缘子串的封挡受力过程,给出绝缘子串的安装形式、封挡控制角度的确定方法和拉力承受范围;分析复合绝缘子串两端挂点的局部杆件受力情况,给出无超应力杆件的撞击点水平活动量和绝缘子串偏移角度。结果表明:随着风速增加,防风偏复合绝缘子串承受的冲击荷载逐渐增加,挂点杆件承受的局部拉力逐渐增加;通过改变绝缘子串安装松弛度,增加导线与绝缘子串撞击点的水平活动量和偏移角度,可以降低局部杆件受力,有效控制风偏角度。

含零值绝缘子高压架空输电线路绝缘子串空间电场分布特性

基于有限元电场仿真方法,研究了110kV和220kV不同绝缘子串型出现零值绝缘子时邻近区域空间电场分布特性,对比合成电场和轴向电场分量对零值绝缘子的敏感度。针对单I悬垂串、双II悬垂串和耐张串等串型,分析零值绝缘子对不同串型的影响程度,定量分析零值绝缘子位置和片数对场强分布的影响特性。结果表明:轴向场强分量对零值绝缘子更为敏感,作为零值绝缘子检测的特征量更为合适;高压侧存在零值绝缘子对电场分布影响最大;对于悬垂双II串应分别测量两侧的场强,以判断零值绝缘子出现位置;连续2片、3片零值时场强下降幅度分别为单片零值的2倍和2.3倍等。

某网球中心轮辐式张弦梁屋盖结构设计与分析

某网球中心屋盖由环形雨棚和中央屋盖组成,两者的平面投影为同心的椭圆形,环形雨棚采用钢桁架结构,中央屋盖经过方案比选采用轮辐式张弦梁结构,均上覆半透明PTFE膜。首先对屋盖的风荷载、积雪荷载、温度荷载取值进行了研究,然后在上述基础上对中央屋盖张弦梁拉索的初始预应力值确定、支座形式、整体稳定性、防连续倒塌、关键节点进行了专项分析。结果表明:中央屋盖自重平衡时,长、短轴张弦梁拉索轴力最大分别为745、490kN;中央屋盖采用径向滑动,切向固定铰支座形式较为合理,其中径向允许位移限值为30mm。采用静力失稳模态法引入整体初始几何缺陷,对网球中心中央屋盖进行双非线性稳定性分析,网球中心屋盖稳定承载力系数满足安全要求;采用拆除构件法中的非线性动力方法进行防连续倒塌分析,网球中心屋盖不会因为张弦梁拉索破断而出现连续倒塌;对网球中心屋盖关键节点进行了专项设计和精细的有限元分析,节点安全可靠。

材料对特高压线路舞动的影响研究

绝缘子串摆动引起的塔头与导线间的闪络事故和金具失效引起的线路故障越来越多,严重威胁输电系统的安全运行和正常供电。采用仿真平台建立输电线路绝缘子串精细化有限元模型,通过改变绝缘子的材料性能,得知不同材料绝缘子串对导线舞动影响较小,对导线风偏也起不到抑制作用。

输电线路更换倒V悬垂绝缘子串轻量化作业方法研究

为快速、高效、安全地完成输电线路倒V悬垂绝缘子串的更换作业,针对更换过程中存在的一系列难题,提出了使用特制机动绞磨机搭配高强度迪尼玛绳及定点限位传递装置的组合装备替代传统工具装备的作业方法,实现了更换工具的轻量化和作业方法的简单化,有效规避了传统更换过程中拆卸、安装作业时存在的弊端,解决了输电线路倒V悬垂绝缘子串导线联板、重锤及绝缘子本体的安装、拆卸等一系列难题,简化了作业步骤,降低了作业人员劳动强度。该作业方法可分解组合,同时适用于其他串型的悬垂绝缘子串,是一种轻量化新型更换悬垂整串绝缘子的作业方法。

不同材料绝缘子串在风荷载下的数值模拟

利用ABAQUS有限元软件建立三档覆冰八分裂导线的数值模型,模拟研究输电线路在不同风荷载下的舞动.基于导线动力特性和舞动特征,分析玻璃、环氧树脂及陶瓷等不同材料绝缘子串对导线舞动的影响,获得特征线路段的舞动响应时程分析、频谱分析与轨迹分析.结合数值模拟结果,进一步对线路在不同风速的风荷载作用下的风偏响应进行时程分析,比较不同材料的绝缘子串对风偏起振现象的抑制效果.结果表明,绝缘子串材料的不同对导线舞动影响较小,对导线风偏幅值起不到抑制效果,因此,在输电线路实际工程应用中,应结合工程造价和防舞性能等因素综合考量选择绝缘子串.