输电线路毕业设计英文

附录外文资料翻译1000千伏交流电源输电线路的雷电保护摘要：首先，结合日本和前苏联在闪电特高压输电线路的性能和分析的特点，以及1000kV输电线路的闪电跳闸率过高经验和教训的基础上，本文作者提出在中国1000千伏输电线关键技术研究中应该减少雷击损坏率的一个关键点，明确提出在防雷保护中保护失效的预防闪络为研究的主要方向。本文提出，降低接地屏蔽线的角度和距离的差距与一个合适的长度是1000千伏输电线路跳闸率减少屏蔽失效一个重要的措施。因此，尤其必须注意防护屏蔽失效的地面延长线更大倾斜的山区线路。在本文中，作者介绍了在中国平原和山区用于特高压输电线路接地屏蔽线的角度以及中国特高压输电线路在最近的两年半的时间里运行情况。目前在中国的特高压输电线路雷击跳闸的故障不会发生了，因此初步呈现出良好的防雷性能。作者还介绍了在中国特高压变电站计算闪电侵入过电压的使用方法和原则和提出并行采取的两个措施降低最高雷电流的屏蔽故障输入线电流截面和优化布置闪电避雷器来限制过电压侵入变电站，因此，会限制需求过电压和避雷器的数量减少。关键词：超高压，输电线路，变电站，雷电侵入波，过电压，1000V对特高压输电线路的防雷性能的研究特征特高压输电线路有两种功能的防雷性能：1）特高压输电线路绝缘水平是非常高的，因此具有引人注目的很低架空地线的可能性和塔顶导致导致发生雷电反击失败。2）塔的高度对特高压输电线是非常高的，因此容易导致屏蔽失败。前苏联特高压输电线路的运行经验[1][2]表明，闪电剔除是输电线路的主要原因剔除。从1985到1994这十年期间，在特高压雷击跳闸次数输电线路是16，占总数的84%数量的剔除。然而，导致闪电剔除的主要原因是导体受到直接雷击屏蔽故障。在前苏联特高压输电线路的地线保护角过大（超过20°），从而导致过高的剥离率使闪电防护失败。在日本1000kV输电线路在同塔双回路线路，已用于500kV电压。1993当它投入运行到九月2007，总共68个跳闸故障发生在传输线，其中67的故障属于雷击跳闸，占总跳闸故障98%。这表明，雷电屏蔽故障的主要原因是特高压输电线路的雷击跳闸故障[4][5]，在日本特高压输电线路雷击跳闸高达0.94次/百公里年利率（计算在同塔双回输电线路的长度）。一个重要的原因在于在弧角较短的距离（5.9米）用于输电线路绝缘子串。中国的闪电定位资料记录的数据表明[6]，中国屏蔽故障导致对500kV输电线路雷击跳闸故障90%。对特高压与更高的绝缘水平，它将更加明显，雷击跳闸的原因主要是屏蔽失败了。因此，中国在特高压输电线路建设中，前苏联和日本的教训应该专门做在这方面为了防止导线是由雷电屏蔽失效的。B.预期闪电跳闸率预期1000kV输电线路雷击跳闸率应低于500kV输电线路，前者可以看作是后者的约70%，即约0.1次/年100公里。因为较少的保证金中国电网较弱的网络结构，为输电线路雷击跳闸率的要求是略高于日本和美国。C.防雷性能计算方法EMTP的计算程序已用于雷电闪络故障的研究。交会法，即，过压波U0和绝缘脉冲放电电压的第二特性曲线相交或不相交，用于模拟领导发展过程中的领导方法已被用于判断是否发生之间的绝缘间隙的闪络。对改进的电气几何模型[9]用于屏蔽故障，应考虑以下因素：对雷电先导的入射角的概率分布；修正系数雷击到地面的距离对绝缘闪络导体的工作电压的影响。在导体屏蔽故障发生时的过电压：式中，屏蔽故障电流的雷电幅值；是导线的波阻抗；是工作电压的幅值；高度的变化的内导体和接地的一个跨接地线。我们还对由一个先导传播模型绕击跳闸率的计算研究（LPM）。然而，计算得到的结果与条件和参数的不同标准向上领袖起源和发展有很大的差异[10][11]。我们认为闪电发展与多复杂的因素影响的物理过程是在一个更详细的考虑的LPM，有其合理性。然而，由于对闪电的物理过程，对一些重要的标准和参数不确定性的知识方面的知识的局限性，它有可能使计算仍有较大的误差。到现在，LPM是在不成熟的阶段，因此它不能直接用于工程计算，但其结果可以用来作为参考。D.雷击跳闸率单回路输电线路塔的类型1000kV单回路输电线路典型塔类型如图1所示，侧相绝缘子串我和中相绝缘子串V.边相导线和塔之间的距离为所需值工作电压的间隙距离的中间阶段和塔之间的强风和距离条件下的控制所需的操作过电压间隙值的控制。雷电冲击间距不为塔头尺寸起着控制作用。换句话说，实际距离在雷电冲击6.7m（海拔500m以下）（a）猫头型塔（b）杯式塔图1.1000kV单回路输电线路塔型闪络跳闸率的计算无论什么样的塔是用什么方法作为绝缘闪络判据，反击跳闸1000kV单回路输电线路速率很低，低于0.0045次/年100公里。因此，对1000kV单回路输电线路，反击不导致雷击跳闸的主要原因。绕击跳闸率的计算特高压输电线路，主要的原因导致雷击跳闸是屏蔽的导体和屏蔽故障减少故障跳闸率的最有效措施是减少地线保护角，特别是在山区的特高压输电线路。电气几何模型进行了雷电绕击跳闸与不同类型的塔传输线率的计算，与地线保护角为小于6°，猫头塔和杯式塔为小于–4°，详见图1。计算的结果列于表1。表1雷电屏蔽故障跳闸率（次/百公里年）塔式地面的倾斜角度（°）0102030杯型ZBS2004.8×10^-90.019猫头型zmp200.00580.1080.618从表1可以看出，（1）降低地线保护角有显着影响降低绕击跳闸率的闪电；（2）地面的倾斜角对绕击跳闸率有很大的影响。此外，足够高的绝缘或特高压输电线路的距离降低屏蔽故障提供了一个良好的基础。特高压输电线路地线保护角的选择根据地形线和地面的倾斜角度变化的一些差异。在中国的特高压输电试验示范项目，建议在平原区和山区杯式塔使用的猫头型塔。接地屏蔽线的角度推导距离的增加，两个地线和中间相的两个地线屏蔽功能的减少之间。无论是雷电屏蔽故障对中间相导体导致上述情况从而导致绝缘闪络，然后断开的线吗?电气几何模型是用在我们的研究分析绕击跳闸率中相导线。以一杯形塔为例，两个姐弟导线的宽度为57.6米，计算的垂直距离之间的地线和导体是13m，用计算结果见表2所示。计算结果表明，在中间相导体的雷电屏蔽故障的可能性。然而，只有雷击的雷电流幅值小（）可以通过屏蔽两个地线，进一步导致屏蔽故障对中间相导体。屏蔽导体雷击等故障幅度远不足以导致绝缘闪络，也不会导致输电线路跳闸。闪电与更大的雷电流幅值只能打击地线不能通过两个地线罢工的方式来屏蔽故障中相导线。因此，对地线屏蔽角的减少可以增加两个接地线之间的距离，而不会造成屏蔽故障对中间相导体，从而导致跳闸的线路。闪电与更大的雷电流幅值只能打击地线不能通过两个地线罢工的方式来屏蔽故障中相导线。因此，对地线屏蔽角的减少可以增加两个接地线之间的距离，而不会造成故障对中间相导体屏蔽，从而导致跳闸的线路。表2雷电流最大可能的屏蔽对中间相导体故障（EGM）塔类型两个接地导线之间的空间（M）导线和地线之间的垂直距离（M）最大雷电屏蔽对中相导线故障电流（KA）ZBS257.6157.91138.84ZMP229.4132.7112.8计算了采用LPM在中国的几个大学，类似的结论。在中国特高压单回路输电线路防雷运行经验随着641km总长度，1000kV交流输电线路的测试和试验项目已于2009一月投入运营，已经运行了两年半，没有任何的雷击跳闸的发生。虽然它的运行时间不长，它已明显表现出与线路雷击跳闸率在日本的特高压输电线路和前苏联的防雷性能比较好。这表明，较高的雷击跳闸率不特高压输电线路的固有特征。如果合理措施的采用，其雷击跳闸率可以降低到一个很低的水平。表3列出了避雷器的作用情况在三个变电站（或开闭站）对中国的1000kV交流输电线路在1月2009和12月2010的两年期和示范工程测试。从表3可以看出，雷电屏蔽故障发生在这三个变电站1000kV输电线路相导线连接（或开闭站）。猫头型塔基本上是用在传输线的南阳荆门段。对长治南阳段，杯型塔使用的基本上都是在长治和猫头型塔侧使用的基本上都是在南阳边。它可以从避雷器，侧相屏蔽故障发生在猫头型塔的作用情况判断和屏蔽故障可能发生在侧相，用杯式塔线中间相。然而，雷电流的幅值不那么大，从而导致避雷器动作，但不引起绝缘闪络和线路跳闸。这些情况符合的计算结果。表3避雷器的特高压变电站的行动名称的变电站对避雷器动作次数侧相中间阶段总次数长治123南阳202荆门303E.雷击跳闸对同塔双回输电线路速率中国首个特高压双回输电线路同塔的建设可能在今年开始。目前，这种输电线路防雷的研究工作已基本完成。塔型和防雷性能在中国，筒式塔采用500kV输电线路，但伞式塔用于1000kV输电线路（见图2）。在这一方面的原因是，伞型塔的防雷性能优于滚筒式塔。计算值的雷电绕击跳闸率的特高压双回输电线路同塔与伞型塔筒式塔列于表4。雷电冲击距离在同塔双回路的1000kV输电线路塔头的大小起着重要的控制作用。所需的值是6.7m（海拔500m以下）。图2鼓和伞式塔表4绕击跳闸同塔双回输电线路速率的计算值（次/百公里年）地面倾斜度（°）鼓形伞型00.1070.084100.280.239反击跳闸率与单回路输电线路铁塔，为双回输电线路同塔的塔建在更高、反击跳闸率也会相对增加。表5列出了闪络跳闸的双回路输电线路建立在相同的塔率的计算结果。表5闪络跳闸同塔双回路输电线路速率塔的类型距离（米）反击跳闸率（次/百公里年）1号线7.20.0117/0.006注意：在“反击跳闸率”栏目，分子/分母分别代表反击跳闸率的同塔双回线路，转换为反击跳闸率为单一的电路线。雷电反击跳闸率转化为一个单回路输电线路为0.006次/百公里年，远远低于预期的雷击跳闸率，占总数的雷击跳闸率比一点。绕击跳闸率以双回路输电线路塔型在图2所示为例同塔，地线保护角伞式塔是–5.4，筒式塔是–3.4，40雷雨天，随着击剔除率表6中列出的计算结果。由于塔的更高的双回输电线路同塔，地球的屏蔽效果，比普通单回路输电线路相对较弱。如果同一屏蔽角，绕击跳闸的线路速率是较高的。三个因素，即地线保护角，地面倾斜角度和导体的最小空气间隙距离塔对绕击跳闸率的重要影响。绕击跳闸与地线保护角减速度的降低，与地面的倾角和降低雷电冲击塔的最小空气间隙距离的增加而增大。这些导致了特高压输电线路雷击跳闸故障几乎屏蔽和屏蔽故障的最大电流是有限的。这是不可能的，过度的雷电流的导体的罢工。间距适当增加可以避免绕击闪络。从表6可以看出，如果使用图2所示的塔的典型类型，与地面倾角小于等于10°地区。地线保护角ɑ是–3.4°，间隙670万和雷电绕击跳闸率为≤0.113次/公里年。因此绕击跳闸率，能够满足预期的雷击跳闸率的要求。表6绕击跳闸同塔双回输电线路速率（次/百公里年）间隙距离（米）保护角(°)地面的倾斜角度(°)0°10°20°30°6.0-5.40.0520.170.6481.781-3.40.0680.2040.7311.94300.1120.2870.9172.2736.7-5.40.0140.0880.4991.427-3.40.0480.1130.5221.57600.0480.1780.6881.8827.1-5.40.0070.0670.3871.308-3.40.0130.0890.4561.45100.0330.1470.6151.7497.6-5.40.0020.0410.2991.129-3.40.0050.0580.3621.26500.0170.1070.5091.548因此，它是在规定的中国国家标准GB／Z24842-2009：（1）对地线保护角特高压双回输电线路同塔，一般不大于3°–平原和丘陵地区，一般不大于5°–山区；（2）雷电过电压的最小间隙距离为6.7m和7.2m（分别对应于500米和1000米海平面以上）[15]。参考文献[1]vereshchagin，吴维韩：对俄罗斯超高压和特高压输电线路的防雷保护的分析，高电压 技术，2号，1998。[2]hk：过电压在高压架空线路和电缆网络和超高压输电线路保护，中国电力出 版社，1996[3]特高压交流输变电（III）：1000kV交流输电线路，中国电力科学技术部部1994[4]谷定燮，新中国对500kV输电线路的防雷保护观念，电力，12号，2004[5]ernational标准的绝缘配合4部分：绝缘配合和电网络模型计算指南，2004。[6]EPRI。传输线参考书345kV及以上（第二版），1982[7][7]里兹克F点模型的输电线路暴露在直接雷击。IEEE跨在电力输送，1990，5（4）：1983~1997。[8]电力科学技术部部，特高压交流输变电（III）：1150kV输电关键技术，1994。[9]谷定燮，绝缘方式选择500伏双回路输电线路在中国，电力，3号，1996。[10]iec71-2。国际标准的绝缘配合2部分：应用指南，199612。[11]埃里克森和周K的简化确定变电站的雷电过电压，操作冲击的代表。国际大 电网会议论文no.33-16，巴黎，1988。[12]人民共和国的中国标准化技术指南：（GB／Z24842-2009）过电压1000kV 特高压交流 输电工程和绝缘配合。2009年11月30日。LightningProtectionof1000kVACPowerTransmissionLinesandSubstationsAbstract：Firstofall,incombinationwithcharacteristicsofthelightningperformanceofUHVpowertransmissionlinesandonthebasisoftheanalysisofexperiencesandlessonsconcerningexcessivelyhighlightningtrip-outrateon1000kVtransmissionlinesinJapanandtheformerSovietUnion,authorsofthispaperputforwardthatoneofthecriticalpointsinthekeytechnicalresearchon1000kVtransmissionlinesinChinashouldbethereductionoflightningfaultrate,anddefinitelypresentthepreventionofshieldingfailureflashoverasthemainorientationintheresearchonlightningprotection.Thepaperpresentsthatthereductionofgroundwireshieldangleanddistanceofthegapwithanappropriatelengthisanimportantmeasureforreducingshieldingfailuretrip-outrateof1000kVtransmissionlines.Therefore,itisparticularlynecessarytopayattentiontotheshieldingfailureflashoverofthelinesinmountainousareaswithbiggerinclinationofgroundalongthelines.thuseithermeetingthedemandofrestrictingovervoltageandreducingthequantityofMOAsused.Keywords：UHV,powertransmissionline,substation,lightning,intrudingwave,overvoltage,1000kVRESEARCHONLIGHTNINGPERFORMANCEOFUHVPOWERTRANSMISSIONLINESFeaturesTherearetwofeaturesinthelightningperformanceofUHVtransmissionlines:1）TheinsulationlevelofUHVtransmissionlinesisveryhigh,thushavingverylowpossibilityofstrikingoverheadgroundwireandthetopoftowerstoresultintheoccurrenceofbackflashoverfailures;2)TheheightoftowersforUHVtransmissionlinesisveryhigh,thusbeingeasytoresultinshieldingfailures.TheoperatingexperiencesofUHVtransmissionlinesintheformerSovietUnion[1][2]indicatedthatlightningstrip-outwasthemajorcauseoftransmissionlinestrip-out.Duringtheperiodofadecadefrom1985to1994,thenumberoflightningtrip-outonUHVtransmissionlineswas16,constituting84%ofthetotalnumberofstrip-out.However,themajorreasoncausinglightningstrip-outisthatconductorswerestrickendirectlybylightningstrokeswithshieldingfailures.TheshieldangleofgroundwireintheformerSovietUnion’sUHVtransmissionlineswasexcessivelybig(morethan20°),thusresultinginexcessivelyhighstrip-outrateoflightningshieldingfailures[3].The1000kVtransmissionlineinJapanisthedouble-circuitlineonthesametower,whichhasbeenoperatingatthevoltageof500kV.From1993whenitwasputintooperationtoSeptember2007,atotalnumberof68trip-outfaultsoccurredonthetransmissionline,amongwhich67faultsbelongtolightningtrip-out,constituting98%ofthetotaltrip-outfaults.Thisindicatesthatlightningshieldingfailuresarethemaincauseofthelightningtrip-outfaultsonUHVtransmissionlines[4][5],andthelightningtrip-outrateofUHVtransmissionlinesisupto0.94times/100km-yearinJapan(calculatedwiththelengthofdouble-circuittransmissionlineonthesametower).Oneoftheimportantreasonsliesatthearcinghornswithashortergapdistance(5.9m)usedforinsulatorstringsoftransmissionlines.DatarecordedbyChina’slightninglocatorsindicate[6]thatabout90%ofthelightningtrip-outfaultson500kVtransmissionlinesinChinaareresultedfromshieldingfailures.WithstillhigherinsulationlevelforUHVtransmissionlines,itwillbemoreobviousthatthecauseoflightningtrip-outismainlyshieldingfailures.Therefore,whenUHVtransmissionlinesareconstructedinChina,lessonsoftheformerSovietUnionandJapanshouldbespeciallydrawninthisaspectinordertopreventconductorstobestrickenbylightningshieldingfailures.B.AnticipatedLightningTrip-outRateTheanticipatedlightningtrip-outratefor1000kVtransmissionlinesshouldbelowerthanthatfor500kVtransmissionlinesandtheformercanbeconsideredasabout70%ofthelatter,i.e.about0.1time/100km-year.BecauseoflessmarginofpowergridsinChinawithweakernetworkstructure,therequirementforlightningtrip-outrateoftransmissionlinesislittlehigherthanthatinJapanandtheUnitedStates.C.CalculationMethodofLightningPerformanceTheEMTPcalculationprocedurehasbeenusedforlightningbackflashoverfailuresinthisresearch.Theintersectionmethod,thatis,whetherovervoltagewaveU0（t）andinsulationimpulsedischargevolt-secondcharacteristiccurveUi—tareintersectedornot,andtheleadermethodusedforsimulatingtheprocessofleaderdevelopmenthasbeenusedtojudgewhetherflashoversoccurornotbetweeninsulationgaps.Fortheimprovedelectricalgeometricmodel[9]usedforshieldingfailures,thefollowingfactorsshouldbeconsidered:Thedistributionprobabilityoftheincidentangleoflightningleader;（2）Therevisedcoefficientofthedistanceoflightningstroketotheground（3）Theinfluenceoftheworkingvoltageofconductorsoninsulationflashover.Theovervoltageonconductorswhenshieldingfailuresoccur:Inwhich,istheamplitudeoflightningshieldingfailurecurrent;isconductorwaveimpedance;andistheamplitudeofworkingvoltage;Theinfluenceofgroundinclinedangle;Thevariationoftheheightoftheinnerconductorandgroundwireofaspantotheground.Wealsomadestudyonthecalculationofshieldingfailureflashoverratebymeansofaleaderpropagationmodel(LPM).However,thecalculationresultsobtainedwiththeconditionsandparametersfromdifferentcriteriaofupwardleaderoriginanddevelopmenthaveabigdifference[10][11].WeholdthatthephysicalprocessoflightningdevelopmentandtheinfluencesofmultiplecomplicatedfactorsareconsideredintheLPMinamoredetailedway,withitsrationality.However,duetothelimitationofknowledgeinaspectofthephysicalprocessoflightningandtheuncertaintyofknowledgeconcerningsomeimportantcriteriaandparameters,itispossibletomakethecalculationhavestillbiggererrors.Uptothepresent,theLPMisatthestageofimmature,thusitisimpossibletobedirectlyusedinengineeringcalculation,butitsresultscanbeusedasareference.D.LightningTrip-outRateofSingleCircuitTransmissionLinesTypeofTowersThetypicaltowertypesfor1000kVsingle-circuittransmissionlinesareshowninFigure1,withside-phaseinsulatorsbeingstringIandmiddle-phaseinsulatorsbeingstringV.Thedistancebetweentheside-phaseconductorandthetoweriscontrolledbytherequiredvalueofworkingvoltagegapdistanceundertheconditionofstrongwindandthedistancebetweenthemiddle-phaseandthetoweriscontrolledbytherequiredvalueofswitching-surgegapdistance.Thelightningimpulsegapdistancedoesnotplayacontrollingroleforthesizeoftowerhead.(a)Cat-headtypetower(b)CuptypetowerFigure1.TowerTypesfor1000kVSingleCircuitTransmissionLinesCalculationofBackFlashoverTrip-outRateNomatterwhatkindoftowersareusedorwhatmethodsareadoptedasacriterionforinsulationflashover,thebackflashovertrip-outratefor1000kVsingle-circuittransmissionlinesareverylow,beingbelow0.0045time/100km-year.Therefore,for1000kVsingle-circuittransmissionlines,backflashoverisnotthemaincauseresultinginlightningtrip-out.CalculationofShieldingFailureTrip-outRateForUHVtransmissionlines,themaincauseresultinginlightningtrip-outisshieldingfailurestoconductorsandthemosteffectivemeasureforreducingshieldingfailuretrip-outrateistoreducetheshieldangleofthegroundwire,particularlyfortheUHVtransmissionlinesinmountainousareas.Anelectricalgeometricmodelwasusedforthecalculationofthelightningshieldingfailuretrip-outrateoftransmissionlineswithdifferenttypesoftowers,withthegroundwireshieldangle<6°forcat-headtowerandthatforcuptypetower<–4°,seeFigure1fordetails.TheresultsofthecalculationarelistedinTable1.TABLE1LightningShieldingFailureTrip-outRate(times/100km-year)TowerTypeGroundInclinedAngle(°)0102030CupTypeZBS2004.8×10^-90.019Cat-HeadTypeZMP200.00580.1080.618ItcanbeseenfromTable1that(1)reducingthegroundwireshieldanglehassignificanteffectforloweringdownlightningshieldingfailuretrip-outrate;(2)theinclinedangleofthegroundhasagreatinfluenceontheshieldingfailuretrip-outrate.Inaddition,thesufficientlyhighinsulationorgapdistanceofUHVtransmissionlinesprovidesagoodbasisforloweringshieldingfailures.TheselectionofgroundwireshieldanglesforUHVtransmissionlineshassomedifferencesaccordingtotopographyalonglinesandthechangeofinclinedangleofthegroundsurface.ForaUHVtransmissiontrialanddemonstrativeprojectlineinChina,itissuggestedtousecat-headtypetowersinplainareasandcuptypetowersinmountainousareas.Thedeductionofgroundwireshieldanglemeanstheincreaseofthedistancebetweentwogroundwiresandthedecreaseofshieldingfunctionoftwogroundwiresformiddlephase.Whetherislightningshieldingfailuresonthemiddle-phaseconductorresultedfromtheabovesituationsoastoleadtoinsulationflashoversandthentrip-outoftheline?Anelectricalgeometricmodelisusedinourresearchtoanalyzetheshieldingfailuretrip-outrateofmiddle-phaseconductors.Takingacuptypetowerforanexample,thewidthoftwogroundwiresiscalculatedas57.6mandtheverticaldistancebetweenthegroundwireandtheconductoris13mm,withthecalculationresultsshowninTable2.Thecalculationindicatesthereisapossibilityoflightningshieldingfailuresonmiddle-phaseconductors.However,onlylightningstrokeswithsmallamplitudeoflightningcurrent()canpassthroughtheshieldingoftwogroundwiresandfurtherleadtoshieldingfailuresonthemiddle-phaseconductor.Suchamplitudeoflightningshieldingfailurestoconductorsisfarinsufficienttoresultininsulationflashoversandalsocannotresultinthetrip-outoftransmissionlines.Lightningstrokeswithgreateramplitudeoflightningcurrentcanonlystrikeongroundwiresandcannotpassthroughtwogroundwirestostrikeontomiddle-phaseconductorinawayofshieldingfailures.Therefore,thereductionoftheshieldangleofgroundwirescanincreasethedistancebetweentwogroundwires,whichcannotresultinshieldingfailurestothemiddle-phaseconductor,thuscausingthetrip-outofthetransmissionline.Lightningstrokeswithgreateramplitudeoflightningcurrentcanonlystrikeongroundwiresandcannotpassthroughtwogroundwirestostrikeontomiddle-phaseconductorinawayofshieldingfailures.Therefore,thereductionoftheshieldangleofgroundwirescanincreasethedistancebetweentwogroundwires,whichcannotresultinshieldingfailurestothemiddle-phaseconductor,thuscausingthetrip-outofthetransmissionline.TABLEIIMaximumLightningCurrentofPossibleShieldingFailureonMiddle-phaseConductor(EGM)TowerTypeSpaceBetweenTwoGroundWires(m)VerticalDistancebetweenConductorAndGroundWire(m)MaximumLightningCurrentOfShieldingFailureonMiddle-PhaseConductor(kA)ZBS257.6157.91138.84ZMP229.4132.7112.8CalculationhasbeenmadebyusingLPMinseveralChineseuniversities,withsimilarconclusionsreached.OperatingExperiencesofLightningProtectionforUHVSingle-circuitTransmissionLinesinChinaWithatotallengthof641km,the1000kVACtransmissionlinetestingandtrialprojectwasputintooperationinJanuary2009andhasbeenoperatingfortwoandahalfyears,withoutanylightningtrip-outoccurred.Althoughthetimeforitsoperationisnotsolong,ithassignificantlyshownagoodperformanceoflightningprotectionincomparisonwiththelightningtrip-outratesforUHVtransmissionlinesinJapanandtheformerSovietUnion.Thisindicatesthatahighlightningtrip-outrateisnottheinherentfeatureofUHVtransmissionlines.Ifrationalmeasuresareused,theirlightningtrip-outratescanbelowereddowntoaverylowlevel.Table3liststheactingsituationofsurgearrestersinthreesubstations(orswitchingstation)ofthetestinganddemonstrativeprojectforChina’s1000kVACtransmissionlinesduringtheperiodoftwoyearsbetweenJanuary2009andDecember2010.ItcanbeseenfromTable3thatlightningshieldingfailuresoccurredonphaseconductorsofthe1000kVtransmissionlineconnectedwiththesethreesubstations(orswitchingstation).Cat-headtypetowersarebasicallyusedintheNanyang-Jingmensectionofthetransmissionline.FortheChangzhi-Nanyangsection,cup-typetowersarebasicallyusedatthesideofChangzhiandcat-headtypetowersarebasicallyusedatthesideofNanyang.Itcanbejudgedfromtheactingsituationofsurgearrestersthatside-phaseshieldingfailuresoccurredatthecat-headtypetowersandshieldingfailurespossiblyoccurredattheside-phaseandmiddle-phaseofthelineusingcup-typetowers.However,theamplitudeoflightningcurrentwasnotsobig,thusresultingintheactionofsurgearresters,butnotcausinginsulationflashoverandlinetrippingout.Thesesituationscomplywiththecalculationresults.TABLEIIIActionsofSurgeArrestersofUHVSubstationsNameofSubstationTimesofActionofSurgeArresterSidephaseMiddlephaseTotaltimesChangzhi123Nanyang202Jingmen303E.LightningTrip-outRateofDouble-circuitTransmissionLineontheSameTowerTheconstructionofChina’sfirstUHVdouble-circuittransmissionlineonthesametowermaypossiblycommencethisyear.Atpresent,theresearchworkoflightningprotectionforthistransmissionlinehasbeenbasicallycompleted.TowerTypesandLightningPerformanceInChina,drum-typetowersareadoptedfor500kVtransmissionlines,butumbrella-typetowersareusedfor1000kVtransmissionlines(seeFigure2).Oneofthereasonsinthisaspectisthatthelightningperformanceofumbrella-typetowersisbetterthanthatofdrum-typetowers.Thecalculationvaluesoflightningshieldingfailuretrip-outratesfortheUHVdouble-circuittransmissionlineonthesametowerwithbothumbrella-typetowersanddrum-typetowersarelistedinTable4.Lightningimpulsegapdistanceplaysanimportantcontrollingfunctionfortower-headsizeofthe1000kVdouble-circuittransmissionlineonthesametower.Therequiredvalueis6.7m(below500mabovesealevel).Figure2.Drum-andUmbrella-TypeTowersTABLEIVCalculatedValuesofShieldingFailureTrip-outRateoftheDouble-circuitTransmissionLineontheSameTower(times/100km-year)GroundInclinedAngle（°）DrumTypeUmbrellaType00.1070.084100.280.239BackFlashoverTrip-outRateComparedwithtowersforsingle-circuittransmissionlines,towersforthedouble-circuittransmissionlinebuiltonthesametowerishigheranditsbackflashovertrip-outratewillberelativelyincreased.Table5liststhecalculatedresultsofbackflashovertrip-outrateforthedouble-circuittransmissionlinebuiltonthesametower.TABLEVBackFlashoverTrip-outRateoftheDouble-circuitTransmissionLineontheSameTowerTypeofTowerGapDistance(m)BackFlashoverTrip-outRate（times/100km-year）IString7.20.0117/0.006Note:Inthecolumnof“BackFlashoverTrip-outRate”,numerator/denominatorrespectivelyrepresentsthebackflashovertrip-outrateofthedouble-circuitlineonthesametowerandthatconvertedtothebackflashovertrip-outrateforsingle-circuitline.Thelightningbackflashovertrip-outrateconvertedtothatforasingle-circuittransmissionlineis0.006time/100km-year,farlowerthantheexpectedlightningtrip-outrate,constitutingalittleratioofthetotallightningtrip-outrate.ShieldingFailureTrip-outRateTakingthetowertypeofthedouble-circuittransmissionlineonthesametowershowninFigure2asanexample,thegroundwireshieldangleofumbrellatypetowersis–5.4andthatofdrumtypetowersis–3.4,withthecalculationresultsofshieldingfailurestrip-outratelistedinTable6.Duetothebiggerheightoftowersforthedouble-circuittransmissionlinesonthesametower,theearthshieldingeffectisrelativelyweakerthanthatofordinarysingle-circuittransmissionlines.Ifthesameshieldangleisused,theshieldingfailuretrip-outrateofthedouble-circuitlineissomewhathigher.Thethreefactors,i.e.groundwireshieldangle,groundinclinedangleandminimumairgapdistanceofconductortotowerhaveanimportanteffectonshieldingfailuretrip-outrate.Theshieldingfailuretrip-outratedecreaseswiththereductionofthegroundwireshieldangle,increaseswiththeincreaseofthegroundinclinedangleanddecreaseswiththeincreaseoftheminimumairgapdistanceoftowersunderlightningimpulse.Thoseleadingtolightningtrip-outforUHVtransmissionlinesarealmostshieldingfailuresandmaximumcurrentofshieldingfailuresislimited.Itisnotpossiblethatthestrokeswithexcessivelightningcurrentstrikeconductors.Anappropriateincreaseofgapdistancecanavoidshieldingfailureflashovers.ItcanbeseenfromTable6thatifthetypicaltypesoftowersshowninFigure2areused,inareaswiththegroundinclinedangle≤10°,Sotheshieldingfailuretrip-outratecanmeettherequirementforanexpectedlightningtrip-outrate.TABLEVIShieldingFailureTrip-outRateoftheDouble-circuitTransmissionLinesontheSameTower(times/100km-year)GapDistance(m)ProtectionAngleɑ(°)Gro