Development in Researches on Reradiation Interference from UHV Power Lines

Reradiation interference(RRI) from ultra high voltage(UHV) power lines has become a hotspot for researches in electromagnetic(EM) interference between UHV power grids and adjacent radio stations.The mechanism of RRI,numerical simulations,methods of protecting distance calculation,and resonance characteristics of RRI are reviewed in this paper using results of works reported by IEEE and Chinese publications.We conclude in this review that RRI at short and medium wavelengths can be simulated using method of moment(MoM) and two commonly used models,the wire model and the surface model,which have different applicable conditions.We indicate that the accurate simulation of RRI at higher frequencies using uniform geometrical theory of diffraction is still beyond our capability because it requires studies of the relative simulation methods.We also suggest that further researches of the mechanism of RRI and the prediction of resonance frequencies above 1.7 MHz are necessary for dealing with the interference between the existing power lines and radio stations because resonance frequencies proposed by IEEE are less than 1.7 MHz.

Overvoltage Suppression for UHV Transmission Lines

The overvoltage phenomena of ultra high voltage (UHV) transmission lines are analyzed and verified by EMTDC/PSCAD simulation. Referring to the theoretical analyses and operating experiences of extra high voltage (EHV) transmission lines in China and UHV transmission lines in Russia and Japan, the methods to suppress the internal overvoltage in UHV transmission lines by protection and control strategies are discussed. Through the cooperation among the recloser, shunt reactor, tripping and closing resistance, and metal oxide varistor(MOV), the overvoltage can be restrained within an acceptable level.

Effects of Un-transposed UHV Transmission Line on Fault Analysis of Power Systems

The conventional fault analysis method based on symmetrical components supposes that the three-phase parameters of un-transposed transmission line are symmetrical in case of fault. The errors caused by the method with the symmetrical distributed parameter circuit model as the equivalent circuit of the un-transposed ultra high voltage(UHV) transmission line were studied under both normal operation and fault,and the corresponding problems arising were pointed out. By contrast with electromagnetic transient and power electronics(EMTPE) simulation results with the asymmetrical distributed parameter circuit model of un-transposed line, it is shown that the conventional method cannot show the existence of negative and zero sequences before fault happening and there are many errors on voltage and current after fault happening which are different with fault types. The error ranges of voltage and current are 2.13%-81.13% and -7.82%- -86.15%, respectively.

The first UHV experimental line section constructed

The first UHV experimental line section of 1000 kV class in China, situated at the outdoor test yard of Wuhan High Voltage Research Institute under the Ministry of Electric Power has been built just before July 1st, 1996. This experimental line section is 200 m long with 3 phase, 8

Measurement and Simulation of Induced Voltage and Current on 110 KV Crossing Transmission Lines under UHV AC Transmission Lines

The induced electricity of 110 kV transmission lines which cross the UHV AC transmission lines may threaten personal safety of the maintenance staff. In this paper, field measurement of the induced voltage and induced current on a 110 kV crossing line inside Jinhua in Zhejiang province is performed. The electrostatic induced voltage on the measured line is 12.24 kV. The power frequency electromagnetic field simulation model is established, and the calculation results are consistent with the measured. Influence factors analysis shows that the electrostatic induced voltage on the 110 kV line is 12.78 kV, the electromagnetic induced voltage is 12.3 V, the induced current through ground wire is less than 1A when the UHV lines operate at full load. The induced voltage and current decrease while the crossing distance increases. Parallel lines induction is much higher than crossing lines. The electromagnetic induced voltage after ground knife-switch shut down would exceed the human safety voltage 36 V while the crossing angle is less than 30?, so the temporary ground wire must be hanged to ensure safety of the maintenance staff.

Fault Locator Using Two-end Unsynchronized Measurements for UHV Series Compensated Double-circuit Lines

An accurate fault location algorithm for double-circuit series compensated lines is presented.Use of two-end unsynchronized measurements of current and voltage signals is considered.The algorithm applies two subroutines,designated for locating faults on particular line sections,and additionally the procedure for selecting the valid subroutine.The subroutines are formulated with use of the generalized fault loop model and the distributed parameter line model is applied.Performed ATP-EMTP based evaluation has shown the validity of the derived fault location algorithm and its high accuracy.

Modeling of Lightning Shielding Failure in UHV Transmission Line Based on Randomness Theory

The operation data obtained abroad indicates that shielding failure in UHV transmission lines mostly accounts for the tripping-out accidents introduced by lightning striking the transmission line.Based on the discharge theories of long air gap and randomness theory,a leader progression model of lightning shielding failure is presented in this paper.The random characteristics of the downward and upward leader are simulated in this model.The ground slope angel is also considered in this model by using coordinate transformation.Moreover,the system voltage is also taken into consideration in this model.The simulation results show that the good agreement between this model and the field data.And the results suggest that return striking exist obviously in UHV transmission line.

UHV输电线路对中波导航台无线电信号的干扰

为分析1000kV特高压输电线路对中波航空导航台的无线电干扰情况,在国家电网特高压交流试验基地进行了飞行试验。利用机载全球卫星定位导航系统(global positioning system,GPS)和地面GPS连续采集直升机穿越特高压线路的飞行数据,采用精密单点定位技术确定飞机航迹,并与理论航迹进行比较。试验结果表明:1000kV特高压线路对中波航空导航台无线电的干扰与飞机距离特高压线路的远近和飞机飞行高度没有明显关系。

UHV输电暂态信号的动力学分析新方法

特高压交流输电线路故障的正确识别与快速切除对于保障整个系统的安全、稳定和可靠运行具有重要意义。通过PSCAD-EMTDC仿真,在比较不同故障类型下故障相、非故障相最大过电流大小的基础上,本文从动力学角度分析了故障信号混沌特征的变化规律。利用Duffing混沌系统对于环境噪声具有较好的抗干扰性的特点,以检测到的故障信号作为该系统的摄动输入,得到了不同故障类型下的相轨迹图,再利用小波边缘检测技术提取到了各相图中的故障指纹信息。最后对某750kV输电线路的故障信号进行了识别,结果表明,该系统具有较好的故障识别能力,验证了该方法的正确性。

UHVAC输电线路大跨越段的防雷保护

为确保特高压输电线路的耐雷可靠性,对晋东南-南阳-荆门UHV输电线路的黄河大跨越段和汉江大跨越段的雷电性能进行了研究并介绍了UHV输电线路大跨越段雷电性能评估的计算方法,同时根据我国输电线路大跨越段的运行情况,参考俄罗斯标准,以大跨越段在雷电过电压下的雷击无故障时间(耐雷指标)来确定防雷保护方案,还计算了UHV输电线路大跨越段的年绕击跳闸次数和年反击跳闸次数及雷击避雷线跨越档距中央的反击跳闸次数,提出了按雷电过电压要求的跨越塔塔头间隙。研究表明,我国特高压输电线路大跨越段的耐雷指标不宜<50 a。

UHV交流输电线路对调幅广播收音台防护间距

为研究特高压交流输电线路对调幅广播收音台的防护间距,通过特高压交流试验基地的实测数据,得到了特高压交流输电线路的无线电干扰水平,为有源干扰的计算提供了强有力的数据支持。利用NEC电磁计算软件,建立了特高压输电线路的实体模型,计算了无源干扰随频率、入射角度以及防护间距的变化规律,得到了特高压交流线路3种典型塔型的无源干扰水平。最后通过比较有源干扰和无源干扰影响,给出了特高压交流架空输电线路对调幅广播收音台的防护间距计算值。

对AC UHV输电线附近可听噪声预测公式的评估

特高压输电中,导线的选择是由输电线下的可听噪声大小决定的,所以可听噪声的预测十分重要。为了从不同机构总结出的多种半经验公式中选择最适合用来预测我国特高压交流输电线下可听噪声大小的公式,结合我国对特高压交流输电线的要求,将相导线水平和正三角排列方式下可听噪声大小的不同预测结果与测量结果进行对比和分析。结果表明:相导线水平排列大雨时可用ENEL公式或IREQ公式计算,小雨时可用ENEL或GE公式计算;相导线正三角排列大雨时可用ENEL公式或BPA公式计算,小雨时只有BPA公式最适合。所以,我国特高压交流输电线下可听噪声的计算在相导线水平排列时选用ENEL公式,相导线正三角方式排列时选用BPA公式。

直流UHV线路杆塔规划及经济档距的确定

为降低直流特高压(UHV)输电线路的工程投资,结合±500 kV和国外已建UHV的经验,分析了现有杆塔荷载和经济档距。根据工程实际情况,计算了塔型方案中各塔的摇摆角系数、水平档距、垂直档距、摇摆角角度及塔头间隙等。计算确定,在理想平地情况下的经济塔高为51 m、经济档距为510 m。研究结果已被应用于云广±800kV线路。

UHV输电线路中绝缘子串电位分布的仿真计算

利用三维电磁场分析软件Ansoft对铁塔、导线、绝缘子按实际尺寸建立三维模型。综合考虑了芯棒、伞群、球头球窝、导线、连接金具、铁塔、均压环等因素对1000kV特高压输电线路中的绝缘子表面电场分布进行了计算。分析了导线、连接金具、均压环、铁塔、三相中其余两相对Ⅰ型绝缘子串和V型绝缘子串电场分布的影响。计算结果可以为绝缘子的正确使用和优化设计提供参考。分析可知,使用均压环可使绝缘子上的电位分布有较大地改善。

Digital simulation studies on long transmission line protection based on balance of energy

The protection based balance of energy is a new technique specially proposed for long transmission lines. This technique depends upon the calculation of net energy into the transmission line by two independent methods and comparing them to indicate healthy and faulty conditions. In order to study the performance and feasibility of the protection based on balance of energy, the new protection has been extensively tested by using EMTP on a long transmission line with various configurations and operating conditions (including single pole line, double circuit lines and two phase operation). The results calculated by EMTP show that under any condition of a power system, the proposed technique has excellent performance,the viability even for high resistance ground faults and a short operation time.

UHV交流输电线路有源干扰下无方向信标台功率限值的分析

有关UHV交流输电线路与无方向信标台电磁兼容方面的研究主要集中在防护距离的分析,对间距无法满足要求时的兼容问题研究较少。为此,从台站频谱参数入手,分析特高压交流输电线路有源干扰下无方向信标台的发射功率限值。首先介绍无方向信标台的工作原理及配置区域,然后分析UHV交流输电线路对台站的干扰机理,最后根据飞行航迹,以防护率为干扰判别依据,结合防护距离的研究,分别针对航路无方向信标台、近距无方向信标台和远距无方向信标台进行有效辐射功率的分析。结果表明,在给定条件下,对于航路和远距无方向信标台,有效辐射功率分别大于5.298 W、5.273 W时,机载无线电罗盘不受干扰;对于近距无方向信标台,与输电线路始终满足兼容的要求,无需分析限值。

特高压输电线路磁场对电力金具材料摩擦磨损的影响

目的通过分析特高压直流线路工频磁场环境对电力金具材料磨损行为的影响,探究其磨损机理,为联接金具的磨损失效预测提供理论依据。方法分析线路实际运行参数,计算工频磁场强度,采用自制电磁线圈与M-2000型磨损试验机相结合,通过分组控制变量法研究额定工况下金具材料的磨损过程,以及不同磁场强度下材料的磨损行为。结果在磁场环境中材料的磨损程度远小于无磁场情况下。在0~800 A/m范围内,随着磁场强度的增加,摩擦因数稍降低,质量损失量和磨损率呈下降趋势。在不同磁场强度下磨损试样均呈现越贴近摩擦接触表面区域其显微硬度越高,且随着纵深向后呈递减趋势。在无磁场情况下,磨损接触表面的犁沟较深,遍布锯齿型边缘的凹坑和山脊型微凸峰。在磁场环境中试样的接触表面和磨屑表面更加光滑平整,且氧含量明显升高。结论在无磁场情况下,接触表面为严重的磨粒磨损和黏着磨损。在磁场环境中,磨损试样在短时间内经历了初期磨合阶段和磨损加剧阶段,从而加速过渡到稳定磨损阶段,由严重的磨粒磨损和黏着磨损加速向轻微磨损转变。稳定阶段的主要磨损机制为氧化磨损,并伴随着轻微的磨粒磨损、黏着磨损,以及两摩擦副与磨屑“阻隔层”之间的三体磨损。工频磁场环境对试样磨损起到了一定的减摩作用,磨损程度减轻。

超、特高压交流线路反时限零序过流后备保护的整定建议

针对国家电网“六统一”线路保护装置,提出了超、特高压交流线路反时限零序过流保护的整定原则。反时限零序过流保护在保证灵敏性方面并无困难,整定原则的核心问题是解决选择性和速动性的矛盾。根据该保护的原理和逻辑提出了转折电流的概念以及接地距离保护与反时限零序过流保护的配合原则;充分考虑配合时间定值和最小时间定值对保护动作特性的影响,综合超、特高压电网实际短路电流水平和接地距离保护的过渡电阻耐受能力,将反时限零序过流保护低电流区的选择性与接地距离保护高电流区的选择性进行结合,提升了对接地故障全域电流范围的选择性切除能力;提出了方向元件投退原则。通过对某省级电网进行算例分析,验证了整定原则的有效性,该整定原则已经在实际电网中进行了应用。

某特高压直流线路地线覆冰灾害分析与探讨

针对输电线路冰灾事故地点覆冰观测数据短缺的问题,以某±800 kV特高压直流线路地线覆冰断线的典型故障为例,尝试从气象要素、现场查勘、影像资料及现场覆冰调查等方面综合分析,结合覆冰形状,选取适当的计算方法估算覆冰量级,为覆冰资料短缺地区覆冰量级的快速确定提供一种简易的计算方法。通过采用不同覆冰条件下导线和地线弧垂间隙反算覆冰量级,验证了此种估算方法的可行性。

±1100 kV特高压输电塔线体系风振响应分析

为研究角度风下长横担输电塔线体系动力响应,采用有限元时程方法分析准东—华东±1100 kV特高压输电线路单塔及塔线体系风振响应。首先,利用线性滤波法计算得到三维脉动风速场,并结合准定常理论得到单塔及输电塔线体系脉动风荷载。其次,建立单塔及输电塔线体系有限元模型,利用模态分析方法计算结构的动力特性,研究导地线及长横担结构对输电塔动力特性的影响。最后,利用有限元时程方法对单塔及塔线体系进行动力分析,研究了风向角、长横担结构及塔线耦合效应等因素对结构动力响应的影响。结果表明:长横担结构会导致扭转频率降低,扭转振型出现顺序前移;塔线耦合效应降低了塔架结构自振频率,提高了结构阻尼比;根据位移均值计算结果,最不利风向角为15°和75°;根据扭转角均方根计算结果,最不利风向角为0°;单塔顺风向响应主要受背景分量和1阶振型的影响,塔线体系还受到导地线低阶共振分量的影响,扭转角主要受扭转1阶振型影响。