华中科技大学硕士学位论文特高压直流输电线路电磁环境的计算研究姓名:周恺申请学位级别:硕士专业:高电压与绝缘技术指导教师:陈俊武20070606I±500kV±800kV6Kaptzov5~8EPRICISPRBPA6ACSR-720/5018m18mIIAbstractWiththeunbalancedistributionoftheenergyandloadcenters,highvoltagedirectcurrent(HVDC)transmissiontechnologyhasabroaddevelopmentprospectsinChina.Withthedevelopmentoftheeconomyandincreasedinneedforelectricity,existing±500kVExtraHVDCwillbeunabletomeettherequirements,UltraHVDC±800kVtransmissionprojecthasbeenputontheagenda.However,withincreasedvoltagelevels,thetransmissionlineenvironmentaleffectsarousedextensiveawareness.TheelectromagneticenvironmentofDCtransmissionlineshasbeenstudiedmuchabroad,buttheresultsaremostlyinEHVlevels.Moreover,itisstillnonsysteminChina,andcannotcopyforeignresearchresultsdirectlyfortheUHVlevel.TheelectromagneticenvironmentofDCtransmissionlinescanbecharacterizedby:DCcorona,totalelectricfield,ioncurrentfield,radiointerference(RI)andaudiblenoise(AN).Theyaremostlyduetothecoronaofthelineswhichiscloselyaffectedbythedistributionsoftheconductorsurfaceelectricfield.Firstly,thethesisgivesaaccuratesolutiononthesurfaceelectricfieldofbundleconductorsbychargesimulationmethod(CSM)withaimprovedaccuracycriteria.Basedontheuniquenesstheorem,usingtheuniquenesselectricfieldofthecheckpointsasthecriteriaofCSMwhichcanbereachtoanydegreeofaccuracy.AdiscussiononthesimulationchargearrangementprinciplesuitablefortheUHVDCmodelisproposed.Theresultsshowedthatthemethodrecommendbyengineeringisunsuitablefor6andabovebundleconductorsSecondly,thethesisgivesadiscussionontheDCcoronacurrentofunipolarlines.Basedonthestudyworksabroad,theunipolarlinescoronaV-Icharacteristicsiscomputing.Thecomputingmethoddoesn'trelyonKaptzovassumption,becauseasimpleandrealisticfunctionthatrelatesconductorsurfacefieldtotheappliedvoltagelevelisincorporatedintotheanalysis.Theresultsareinbetteragreementwithexperimentaldata,andshowedthatforaunipolarUHVline,thecoronalossis5~8timestotheEHVlineandwillbemoreseriousforbipolarlines.IIIThirdly,thethesisgivesthecomputedresultofthetotalelectricfield,ioncurrentdensityandiondensity,usingthemethodrecommendedbyEPRIofU.S.A.Electricalparametersaswellasdifferentseasonsandweathersaretakenintoaccount.Theresultsshowedthatthetotalelectricfield,ioncurrentdensityandiondensityhaveconsistentdistributionrules,increasingtheHeightoflineortheradiusofconductorscanreducethetotalelectricfieldlevel.Finally,theRIandANlevelsofUHVDCarecomputed,andadiscussionabouttheinfluencefactorsoflineparametersisproposed.Theresultsshowedthat,foraUHVDCtransmissionline,using6ACSR-720/50conductors,withaheightabove18m,poletopoledistanceabove18m,thetotalelectricfield,RIandANwillhavethesamelevelofEHVDCtransmissionlines.Keywords:UHVDC,transmissionline,electromagneticenvironment,corona,thetotalelectricfield,RI,AN111.11.1.12/32/32/3[1][2][3](1)1/3(2)1/3(3)(4)(5)(6)500kV500kV800kV800KV22006200920106400MW1.1.2123800KV32/3[4][5]500KV500KV[6]1.2[7][8]()[9]1.2.141.2.2[10]CIGRE3[11]1.1[12]51.1mA60Hz1.0.00250.032.1.00.60.40.33.5.23.51.10.74.9.06.01.81.25.99.5%62419.06.01.21.222kV/m273240[13]DL436-91[14]500kV1.31.3500kV30kV/m100nA/m2~500kV4kV/m1.2.31.4EPRIEPRI[5]50dB500kV61.4dBA400kV30.038.0600kV48.059.5~500kV29.034.0~500kV58.568.0(DOE)4045dB(A)50%BPA40dB(A)50%40dB(A)[3]1.2.4/PLC1.1[9]101001k10k100k1M10M100M1GHzAC-harm502.5PLCtelephoneinterferenceRI304001002.54004004004corona1.120dB[15]20dB728dB450KV30m40dB380KV50dB80%53~58dB50dB50%500kV55dB1.31.3.1BonnevillePowerAdministrationBPA1963~19687Dalles5375500kV[16]EPRI[17]EPRI[18]1971NelsonRiver465kV1985500kV[19][20]EPRIIREQNelsonRiverDossenwald60400kV[21]CIGREIEEE81.3.280500kV(DL436-91)20076200712[22]1800kV23/4800kV91.3.31)800kV2)1.41)2)63)V-I104)EPRI5)6)112分裂导线表面电场的精确计算2.1引言考虑到经济性,输电线路通常设计成在正常运行电压下允许有一定程度的电晕放电[23]。线路的电晕放电,将会引起电晕损失、无线电干扰以及可听噪声等一系列环境问题。在特高压情况下的环境问题更是引起人们的广泛关注。研究表明这些环境参数与导线表面电位梯度(电场强度)密切相关。因此精确计算导线特别是分裂导线表面电位梯度具有重要的工程意义。2.2工程中常用的计算方法目前工程中计算分裂导线表面电位梯度的方法主要有三种:1,国际大电网会议CIGRE及国际无线电干扰委员会CISPR推荐的马克特-门格尔法;2,Sarma和Janischewskyj提出的逐步镜像法;3,模拟电荷法。方程部分22.2.1马克特-门格尔法(MarketandMengele)1)为了求取各个相导线的电荷,按照保持对地电容相等的原则,将分裂导线用虚拟的等效单根圆柱形导线代替,其半径由下式给定:1eqnnrrRR⎛⎞=⎜⎟⎝⎠(2.1)式中,R——分裂导线的半径(cm);n——子导线的根数;r——子导线的半径(cm)。2)用麦克斯韦电位系数法决定每根等效导线的电荷Q,此即导线上的总电荷:[][][]-1QPU=(2.2)式中:[Q]和[U]分别是导线上的电荷和电压的列矩阵,而[P]是由导线的自电位系数和互电位系数组成的矩阵,它们可以直接用镜像法求得。3)把分裂导线作为孤立导体对待,即忽略了其它相线的影响,并认为总电荷均匀分配在每根子导线上,每根为Q/n。按此,分裂导线中子导线的平均表面电场强度12由下式计算:av0eq2QEnrπε=(2.3)4)由于屏蔽效应,实际表面场强在分裂导线外部要更大些,而在内部则小些。分别计算分裂导线的平均昀大及平均昀小表面电场强度:()()maxavminav1111rEEnRrEEnR⎡⎤=+−⎢⎥⎣⎦⎡⎤=−−⎢⎥⎣⎦(2.4)沿导线圆周上任一点t的电场强度则由下式计算:()tav11cosrEEnRθ⎡⎤=+−⎢⎥⎣⎦(2.5)式中θ——Et与Emax之间的夹角。5)对于双极直流线路Mangoldt提出可以用每千伏梯度的梯度因子'G(kV/cm/kV)来近似计算导线表面电位梯度[24][25]。()'12121(1)2ln41nnrnRGHnrHnrRS−+−=⎡⎤⎢⎥⎢⎥⎢⎥+⎢⎥⎣⎦(2.6)式中:G——导线表面点位梯度,'GVG=,kV/cm;r——分裂子导线半径,cm;R——通过分裂导线中心圆周的半径,cm;H——导线平均高度(导线对地昀小高度加1/3弧垂),cm;S——正极与负极之间的距离,cm;n——分裂导线分裂数。需要注意的是,采用上述方法计算导线表面场强,一般能满足工程需要,但该法不能计算子导线的表面场强。对于子导线表面场强,由于相分裂子导线同极性电荷的13作用,使沿子导线表面的电荷和电场强度的分布都不均匀。该方法虽然计算简单,但不能反映分裂子导线表面场强,对于更高精度的计算要求不能满足[23]。由于电晕效应对导线表面场强非常敏感,必要时还需要采用更精确的方法来计算,常用的精确方法有逐步镜像法和模拟电荷法等。2.2.2逐步镜像法这种方法的基本原理是在一个多导体组成的体系中,每一导体用一系列置于该导体内的镜像电荷来代替,使表面维持等电