小电流系统.docx

一、概述summary小电流系统是指中性点不直接接地系统，包括中性点不接地系统，中性点经消弧线圈接地系统或中性点经电阻接地系统。在我国，66KV及其以下电压等级的电网中，一般都采用这种系统。Lowcurrentsystemisneutralpointindirectearthingsystem,containingneutralpointunearthingsystem,neutralpointearthingsystemthrougharcsuppressionooilorneutralpointearthingsystemthroughresistance.InChina,66KVpowerplantandothervoltagelevelswhichislessthanitapplythiskindofsystem.小电流系统发生单相接地以后，由于故障特征不明显，使得能迅速、准确地指示接地回路有了一定的难度，小电流系统单相接地选线一直是继电保护领域未彻底解决的一个难题。从八十年代末一直到现在，众多大专院校、研究院、生产厂家都致力于这一产品的开发与生产，提出了不少新思路与新方法。Whenthelowcurrentissinglephaseearthing,becauseoftheunobviousfault,itisalittledifficulttoindicateearthingcircuitquicklyandcorrectly.Thewire-selectoroflowcurrentsystemsinglephaseearthingisalwaysanunsolvableprobleminrelayingprotectionfield.Fromtheendof80stonow,lotsofcolleges,institutesandmanufactureshavebeendevotingtodevelopthiskindofproductandadvisemorenewmindsandideas.目前国内流行的三种选线原理是功率方向方法、谐波分析法(即群体比幅比相法)、与信号注入法。Inthepresent,threepopularselectingprinciplesarepowerdirectionway,obliquewaveanalysis(comparegroupmagnitudeandphase)andinsertingsignal.(1)功率方向法：采用判断每条线路的零序电流的功率方向来确定故障线路，这种方法从原理上讲就做不到100%的准确率，可能出现一条线路接地，判断多条线路或一条都判断不出的结果。目前，这种方法常被综合自动化系统中分布采样单元或功率方向继电器采用。Powerdirectionway:itdefinitefaultcircuitbyjudgingpowerdirectionofanycircuit'szerosequencecurrent.Itcan'treachto100%accuracyaccordingtotheprinciple,itmaybesinglephaseearthing,judgemanycircuits'directionornone.Today,thiskindofmethodisappliedindistributingsamplesofintegratedautomaticsystemorpowerdirectionrelay.(2)谐波分析法：谐波分析法采用单相接地后零序稳态信号的群体比幅比相法，由于比幅比相时，采用的是相对原理，因此，这种方法从理论上讲不存在死区，不受运行方式及接地电阻的影响，可以做到100%的准确率，其选线方案的有效性已得到充分证明，但对于CT不平衡导致的零序电流，这种方法不能有效解决。Harmonicwaveanalysis：itappliesthewayofgroupcomparingmagnitudeandphaseofzero-sequencesteadysignalaftersingleearthing.Becauseoftherelativeprincipleusedingroupcomparingmagnitudeandphase,sothereisnoblindspotintheory,anditisnotinfluencedbytheoperationwayandearthingresistance,andreachtotheaccuracyrateof100%.Itsavailibilityofwire-selectingisprovedsufficientlyButforthezero-sequencecurrentcausedbyunbalancedCT,thiswayisunavailable.（3）信号注入：虽然接线简单，不需零序CT回路，但由于注入信号大小及方法的限制一般主要用于10KV及以下电压等级系统。另外，探头的灵敏度和可靠性易受各种外界因素影响，再者综自站及无人值守站的使用有些不便。Insertingsignal:althoughitiseasytoconnectwiresanddoesn'tneedthezero-sequencyCTcircuit,itismainlyusedin10KVvoltagesystemorlessbecauseoftherestrictionsofstrongorweaksignalandinsertingway.Moreover,thesensibilityandreliabilityofthedetecterareeasytobeinfluencedbytheotherfactors,anditisunconvenienttobeappliedinautomaticandunattendedsubstation.二、选型须知optioninformation型号选线路数通讯功能打印功屏体开孔尺寸图接线图ModelRoutesofcommunicati能DimensionoftheholeFigureofselectiononprinterontheboardwiringBW-MLVC33W42有有HYesyes注：通讯口提供RS232和RS485接口，可以通过装置内部拨码开关设1H闰Notes:thecommunicationportsuppliestheinterfaceofRS232andRS485,itcanbesetbythedial-upswitch.三、装置的主要特点Majorcharacteristics of the deviceBW-MLVC33H系列微机小电流接地选线装置是在BW71L196H型基础上重新开发设计的新一代微机小电流接地选线装置，主要有以下特点：BW-MLVC33Hseriesmicrocomputerselectiondeviceoflow-currenteathingsystemisdeveloppedanddesignedonthefunctionofthemodelofBW-ML196H,majorcharacteristicsisinthefollowing:1 .选线方案上综合利用了暂态过程的小波分析法及利用稳态过程的谐波分析法与能量法，进一步提高了选线的准确率。Theselectionwayusessmall-waveanalysisoftransientstateandharmonicwaveanalysisofsteadystateandenergymethod,thisenhancestheaccuracyofselection.2 .严格按照继电保护装置的要求来设计，制造和检测。Itmustbedesigned,manufacturedandcheckedaccordingtotherequirementsoftherelayprotectiondevice.3 .全新的硬件系统，大量使用新型贴片元件以提高装置的可靠性。采用美国TI德州仪器公司出品的高性能硬件浮点32位DSP微处理器TMS320VC33作为本装置的微处理器，从而大大提高了本装置的运算速度和精度，为准确选线提供了强有力的支持；采用赛灵司Xilinx出品的大规模高速CPLD作为本装置外围电路控制核心；装置内设置了BURR-BROWN公司的高速模数转换器进行高速模拟信号的数字化转换；板载超大容量高速RAM、FLASH以储存大量的数据信息，提高运行速度；采用超高速CMOS电子开关，一次ON-OFF操作仅需60纳秒。Thereisanewhardwaresystem,andenhancingthereliabilitybyusingabundantnewsmdcomponents.Itapplies32statusmicro-processorTMS320VC33ofhigh-performancehardwarefloating-pointmadeinTITexasappratusCoofAmericaasthemicro-processorofthedevice.Sothespeedandaccuracyofoperationareimprovedbroadly,itsuppliesgreatsupporttotheaccurateselection.Ituseshigh-speedCPLDmadebyXilinxasthecontrolcenterItisinstalledhigh-speedmodulusconvertermadebyBURR-BROWNtoconverthigh-speedanalogsignal,high-speedRAMandFLASHwithgreatcapacitancecanstoreabundantdatainformation,enhancingoperationspeed.ItappliessuperspeedCMOSelectricswitch,onceon-offonlyneeds60nanosecond.4 .人机界面非常友好，采用液晶汉显屏，信息量大，调试信息丰富，操作简单。TheinterfaceisfrendlyandappliedLCDscreenwithChinese,maximumamountofinformation,abundantadjustmentinformation,easyoperation.5 .选线准确率高：直接接地、间隙性接地、弧光接地均可准确选线。High-accuracyselection:directearthing,gapearthingandarcearthingcanselectwiresprecisely.6,易于和综合自动化及远动装置接口。提供RS232、RS485通讯接口，并且提供了继电器节点输出信号，继电器节点输出信号的输出方式可以在标准输出、BIN编码输出、BCD编码输出方式中任意选择。Easytoconnecttointegratedautomationandremotedevice.ItsuppliesRS232andRS485comunicationinterface,andalsosuppliesnodeoutputsigna