某工厂供电系统的设计说明书

1LANZHOUUNIVERSITYOFTECHNOLOGY毕业设计(论文)禽题往目古某工厕厂供钥电系眉统的计设计躬学生处姓名糕流学哗器号见专业邀班级惩驱指导潜教师圆叛学炎润院艘电信异学院巴辩论钟日期销离20晶13请.0问6.侦171摘要统作为看当今暑工业肚开展浑最重侍要的绸能源项和动唐力，草电能浸既可尼以由满其他衡能量鹿转化禽也可盐以转纯化为次其他咱的能店量。罩电能涝的输防送和碑分配族具有文可靠盲、经嚼济、潜平安牌、快晚捷的怨特点肠。电透力用态户包等括工追业、音农业连、交丰通运熄输等榴国民夺经济究各个事部门厅以及移市政鼠和居额民生篇活用吃电等闸。因网此，帆保证刘可靠游、安钳全、搂经济丑、高乘质量椒的供依电对盈于工根农业聪的生茧产和锻人民萍生活射有着敞很大洗的影枯响和莫重要浆意义语。雁冶金惰厂供密配电秧设计川应根坚据各螺个车遵间的虚负荷指数量坊和性猛质、仙无功也补偿拨、变仆压器仗的台候数和抚容量乘的选赵择、密短路翠电流素的计乔算以省及变渐电所啊上下亮压侧袜电气壁设备丘选择族等因炸素，鉴从而筹为该阅冶金暖厂提蛋供安帝全可茅靠、京优质珍的电璃力资亡源，裤并可峰最大川限度狐的减辛少公眠司的兵资金路投入和和降泥低运宽行成船本。净使用钟的方塔法：维工厂顶的供帖配电轨设计味应考更虑多损个方检面，支运用偿负荷拥计算著，变蛾压器失容量糕、型摸号、怜数量袍的计艘算，部无限医大容食量电稳源系罩统供铸电时杰短路拘电流纸的计把算，煤以确唉定各毅上下绞压侧席电气氧设及责导线邮的规瑞格，热再进衡行变贴压器裕继电将保护抹装置价的设炉计和致整定她以及域防雷衰接地柔设计拨。图最终风为本单冶金供机械脊修造特厂设糟计一敲个安找全可办靠、恒经济宫合理内、技哪术先乎进的冒供配沈电控容制系钥统图薄，满蹲足该假设厂的菠生产效需求嗓。衔关键飘词掉：毅电力挖系统探；继页电保皂护；逼供配绿电；腐负荷迎计算确；短狼路电锡流1恩Ab棍st死ra纷ct煎As僚o陕f紫to暂da进y'真s被mo掉st博i龟mp签or叫ta芽nt均i食nd右us躺tr纠ia皂l毁de劈ve善lo日pm滥en标t桌of丧e蔬ne变rg龟y藏an炎d额po田we己r,温p姜ow司er绘n创ot采o堆nl所y近by周o该th茂er虚e甩ne离rg勾y询co致nv床er磨si熊on作c拢an溪a堤ls宿o欠be图c帆on洋ve饭rt剑ed勇i裳nt蚊o银ot己he浓r蓄en向er蕉gy裁.启El抓ec昌tr钓ic斥it露y颈tr建an帝sm球is昨si效on熔a春nd还d耳is外tr屯ib说ut留io年n结of钳r散el桶ia暑bl用e,闸e显co蜜no饭mi密ca倘l,罩s梳af架e,不f碰as棍t.虑E蠢le际ct乐ri锦ci忘ty钉u笼se桶rs召,卸in蚁cl夺ud酸in栽g消in臂du搂st受ry极,路ag桌ri隐cu盒lt倚ur络e,蛋tr痰an浩sp有or虎ta笔ti热on全a轻nd妈o销th昼er舍v延ar鲜io剧us萄n优at收io结na溉l狠ec怨on测om善ic叠s剖ec拾to橡rs未a好sw讯el粉l位as挡m米un股ic胁ip角al控a毛nd融r细es叮id污en街ti掩al五e绢le善ct宾ri墨ci渣ty皂.鲁Th她er帅ef片or帝e,舰t张o笔en毕su满re闲r蹦el和ia幻bl汗e,铁s信af旺e,丝e巨co脾no宾mi银ca础l,都hi肯gh洞q骡ua队li仔ty僵p咬ow市er子s拦up翁pl辉y躲fo淋r狐in敏du楚st桨ri吐al弱a绩nd创a走gr慰ic商ul裳tu舱ra赵l辣pr序od回uc善ti龄on膊a近nd已p叉eo虹pl揉e'斤s瞎li寄ve宣s状ha乔ve奋a隶g凝re绘at膝i汉mp筐ac宪t研an盾d笋si退gn躺if津ic碎an口ce持o鼓f勇.轰Me迷ta纷ll圆ur酬gi求ca技l罚pl吓an线t燕fo饿r渗di瓦st塑ri访bu镰ti块on弊d鸟es刑ig用n允sh辈ou翅ld素b伏e魂ba跃se销d剧on骄t孝he臭n剩um动be绞r乌an寿d命na贤tu沉re否o畅f赛ea墨ch吓w苗or害ks祸ho篮p锄lo份ad雪,凉re乓ac料ti暖ve烫p左ow笋er艳c握om受pe厦ns截at套io酱n,败t盈ra增ns额fo牙rm由er蛛s绪ta岗ti啄on读n足um病be揉ra宗nd咱c守ho栏ic盼e稀of弯c多ap难ac狡it井y,辰t面he朱c欠al矩cu末la贼ti驰on椒o写f东sh辰or行tc返ir桨cu贸it乒c范ur拥re肤nt验a纳nd申t做he腔s盟ub摄st度at跌io桑n削hi留gh污a灰nd词l做ow驴p遭re桃ss车ur丹e舞si撞de摇o存f努th玉e纹el燥ec特tr讽ic粉al纳e副qu休ip染me问nt牵s遵el轧ec令ti浸on西a馆nd箭o运th冠er劳f耻ac舱to执rs到,雕wh狼ic由h滋fo属rt伴he并m紫et鞋al撑lu名rg膀ic沿al驼p裤la猫nt钓p跨ro矿vi奏di谷ng统s容af存e,骑re敞li刑ab拔le冬,广hi体gh向-q举ua晌li目ty肉p姐ow差er波r叛es溜ou豆rc疼es弹,雄an解d养ca电n首mi部ni时mi溉ze雄t宰he槽c丑om棍pa独ny呼's秃c殖ap叼it区al速i晨nv艘es禽tm膏en弯t季an版d铅lo铲we有r处op孝er健at拼in羞g托co氏st缝s.炒U芒si晌ng箭t过he罗m洗et较ho闻d:喝t在he扩悄pl露an胡t伶fo红r贯di弓st捆ri燥bu疑ti揭on谢d遗es磁ig支n峡sh海ou忍ld纺t香ak径e按in兄to响ac缓co叠un育t惰va剑ri叙ou局s尖as荒pe狠ct六s,扫t匙he饮u窑se踩o透f驾lo国ad钢c氧al巷cu输la炮ti妈on仁,主tr脾an骡sf格or准me崇r扩ca伍pa洲ci踪ty备,胳mo土de妻l,视q爬ua启nt谈it甚y芹ca美lc谋ul再at秀io帅n,卫t优he远c资al肺cu酬la紫ti皆on胞o摄f偷th施e淡in妄fi侵ni虎te芳b匹ul稠k扯po萍we挣r弯sy桶st吹em游s鹿ho顶rt冤-c诵ir醉cu客it残cu苗rr傍en扯t趴wh胀en蚕p窗ow贼er拥ed挪t楚o圣de胳te臣rm浅in搜e煎th右e距hi娱gh盘a泻nd湾l版ow掠p犬re飘ss啄ur净e雅si踩de犁o渡f肉th路e索el条ec串tr局ic族al绑e熄qu兰ip辛me像nt爸a床nd确w挡ir您e树sp须ec课if彼ic倒at远io法ns钟,悉de掘si陈gn闹a穿nd孤t猎un惊in保g缠of酿t絮ra牲ns畅fo挨rm佩er为p刺ro倒te旱ct蓄io泥n笛de秀vi必ce察s,攻a控nd耍l茅ig允ht喷ni奏ng替p圆ro置te召ct秧io床n偏an施d惜gr赏ou颤nd介in费g宾de预si论gn百.F甜in理al与-b窝as岗ed茂m匪et衬al之lu艇rg吊ic岗al俗ma宏ch慎in僻er盲y朱re止pa喜ir脉w超or井ks息ho号p奴to断d判es陪ig老n绵a岭sa演fe膛a航nd德r颈el渴ia遭bl疼e烟an射d命ec层on奋om罢ic献al洽ly库r偶ea陶so承na什bl西e,冬t或ec旅hn替ol通og伞ic额al扮ly什a庙dv扣an适ce摊d岸po装we问r堆su厉pp挨ly布c溜on铁tr训ol读s服ys随te间m崭di鬼ag犁ra庭m辞to搞m晶ee坡t荒th同e括pr障od便uc铲ti眉on苏n缸ee德ds痕o岩f吓th吨e葵pl绍an论t.纯锯Ke握y踪wo责rd士s：而Po艇we皂r企sy蓬st丘em曲s;艇p仗ro押te值ct务io婆n;洗s虽up缴pl雪y蜘an离d护di家st旱ri配bu格ti暖on葬;护lo秆ad巴c激al要cu针la众ti劣on社;帆sh刮or耽t-旬ci锐rc乏ui肌t页cu晕rr哗en叉t1阻目蜜祝录TOC\h\z\u\t"标题1,1,标题2,2,标题3,3"煎摘虫要杆⑷偿应充柜分考鸡虑工茂厂以兄后扩节建的乌需要斑，本秩可持铃续的枕思想伏融入浪以后伴的设注计过辨程中趋。光但提是本项设计双限于红自己厚能力声有限屈，设庆计过脑程难绪免会例出现涝错误微和不汉足，消望老棕师和狸同学枣批评殖指正墨。佳参型考百文扁献骑[康1探]挣王荣悔藩.茶工艰厂供唱电设懂计与殖实验洋.少天津豆：天岂津大莲学出她版社均，2蛋00棋2.她巷[谊2妻]督刘介桃才.伯工塞厂供润电简怜明设球计手色册.属北批京：境机械刷工业李出版让社，恳19确93娘[3炮]桂苏能文成盲.蒜工厂副供电记.蹈陕西狼：北秋京：科机械奏工业催出版光社,夜2特00敞2.饰[那么4蜜]医别欺朝江纺.晋配电屡系统甚可靠击性评百.北托京：果中国办电力妨出幅员社,没1量99差7陈[限5华]歇沈释根才尽.中订国电绣力百苍科全私书.贺北燃京：正中国蒜电力恶出版视社,膊1跌99均7.前警[某6棍]雾余感建明欲，同标向前工，苏字文成养.供栋电技俯术[嗽M]喊.北法京：惑机械反工业始出版改社，款20雁08柜.含[茧7最]侧刘俘继春俩.发故电机望电气心设计絮与C饺AD平应用溪[D缸].肢四川雄：四搜川大愤学，跳20班03侄.鸡[马8耀]删刘增破良,孤刘国奸亭.宝电气枣工程携CA竞D.灾北京川：中册国水盖利水六电出钢版社匙,2蛛00旗3.队粉[竟9间]百王荣卡潘.脏工厂玩供电鸽设计嚼与实赢验[复M]购.天芳津：亏天津伴大学在出版预社，嫩19祖89王.不[蒜10周]毛唐志黎平.细供配践电技主术[缠M]可.北我京：抵电子笨工业蹦出版睡社，棒20腿05狗.朴[1模1侄]伸刘介糟才.柳工厂软供电捕:第市四版值.北勤京:海机械践工业旁出版零社,旋20殖04味.缝[撞12鼻]写余键抢明等坚.供饮电技绿术:班第三讲版.变北京柄:机乓械工淡业出慢版社诚,1授99本8斑.缎[漂1雨3]厨刘介舱才.碧实用介供配丑电技恢术手出册.荐北京得:中培国水抖利水犯电出而版社抢,2避00吵2阀.押[屋1肆4]葵黄德罩仁等饱.供耐用电纺实用劝技术些手册再.北拨京:然中国塌水利究水电厘出版炎社,江19崇96翼.芽[欠1外5]础中国昂航空府工业里规划遍设计谜研究恭院.双工业稀与民榜用配处电设糠计手琴册:练第2笑版.图北京悠:水胆利酒电力冶出版口社,贯19允94袋.哥[聋1圈6]栏刘介匠才.棉工稍厂供考电设衣计指言导.鲜北京协:机倾械工辉业出旗版社谢,1友99酒8逐.煮[析1扑7]蔽工厂孟常用材电气缝设备谢手册堂(上者册)东.北距京:乐水利戏电力焦出版晋社,说19批83丙.本[介1广8]膨郭仲狮礼.腿高压拳电工歉实用讯技术心.第慧2版相.机锣械工洽业出霞版社糊,2侍00薪0竿.笋[纤1慢9]圾杨卫扔东.输工厂肤供配愈电.狂北京终:电芬子工智业出突版社兄，2割00剖2坛.伍[善2舅0]浪周裕过厚.地变配壤电所雹常见泽故障钉处理郊及新樱设备认应用肤.摩北京涛:中刚国物渠资出熄版社今,2络00呀2袭.盟[骂2创1]刷刘换介才绍.掘工厂煤供电岛[云M]咬．越北京床：机新械工据业出野版社等，片20池0绒3.匪44缺-4闪8隐.俊[伴2叔2]捉王稳健明厚，苏破文成冲．供坡电技骡术幅[M生]龄．西猜安：诵电子鹅工业魔出版左社，于20融0高4．球[油2向3]划何数仰赞筛，温潮增银污．电样力系豪统分庸析倍[M哥]康．武帐汉：茫华中糊科技杜大学缘出版薪社，肿20瓶04赠．抄[肾2倾4]言张荷桂香挨．机因电类包专业称毕业披设计宽指南佳[抓M]御．瑞北京递：机劈械工句业出偏版社撑，2叶00堵5．趁[矮2哭5]咱江鉴文，狮许慧誉中．腹供配野电技熟术匪[M构]扩．北胡京：隐机械踏工业冻出版万社，里20原03拥．菠[菠2们6]贵李具梅随.耍电工幸根底殖[躲M]绑．拔北京袜：中零国电埋力出何版社犹，2岭00炊4．效[董2甚7]泰项达根，斥曾克失娥．眯电力淡系统薪继电芳保护酸原理挥与应点用弓[M晴]累．武功汉：呆华中戒科技叠大学呢出仔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tionoftimethatacomponentorsystemisoutofserviceduetofailuresorscheduledoutages.Analternativedefinitionisthesteadystateprob-abilitythatacomponentorsystemisoutofserviceduetofailuresorscheduledoutages.Mathematically,unavailability¼(1–availability).Failurerate:Themeannumberoffailuresofacomponentperunitexposuretime.Usually,timeisexpressedinyears,andfailurerateisgiveninfailuresperyear.Meantimetofailure(MTTF):Themeantimeuntilacomponent’sfirstfailure,forcomponentswithawearoutfailuremode,suchasincandescentlightbulbs.Meantimebetweenfailures(MTBF):Themeanexposuretimebetweenconsecutivefailuresofacomponent.Itcanbeestimatedbydividingtheexposuretimebythenumberoffailuresinthatperiod,providedthatasufficientnumberoffailureshasoccurredinthatperiod.MTBFsobserved(repaireditems):Forastatedperiodinthelifeofanitem,themeanvalueofthelengthoftimebetweenconsecutivefailures,computedastheratioofthecumulativeobservedtimetothenumberoffailuresunderthestatedconditions.1)Thefailurecriteriashallbestated;generally,themaincriteriaisfailuretoconformtospecification.2)Cumulativetimeisthesumofthetimesduringwhicheachindividualitemhasbeenperformingitsrequiredfunctionunderthestatedconditions.3)ThisMTBFisthereciprocaloftheobservedfailurerateduringtheperiod.4)MTBFdoesnotindicateusefullife.Meantimebetweenremovals(MTBR)observed:Themeanvalueofthelengthoftimebetweenconsecutiveunscheduledunitremovals,computedastheratioofthecumulativeobservedserviceyearsofinstalledbasetothenumberofhardware,unrepeatable,software,ormanufacturingprocessfieldfailures.Removalrate:Themeannumberofremovalsofacomponentperyear,thatis,1/MTBR.Outage:Thestateofacomponentorsystemwhenitisnotavailabletoproperlyperformitsintendedfunctionbecauseofsomeeventdirectlyassociatedwiththatcomponentorsystem.Interruption:Thecompletelossofvoltageforatimeperiod.Thetimebaseoftheinterruptionischaracterizedasfollows:Instantaneous:0.5–30cyclesMomentary:30cyclesto2sTemporary:2sto2minSustained:greaterthan2min.Inducedfailure:Failureattributabletotheapplicationofstressesbeyondthestatedcapabilitiesoftheitem.Initialqualityerrorrate(IQ):Thenumberoffailuresoccurringduringthefirsttwodaysofownershipofaunit,expressedasapercentofthoseunitstestedorplacedinservice.Maintenanceindicator(MI),observed:Themeanvalueofthelengthoftimebetweenconsecutiveunitfailures,removals,andsoftwareupgrades,computedastheratioofthecumulativeobservedserviceyearstothenumberoffailures,removals,andservice-bulletin-relatedupgrades.Usefullifeorservicelife:Theperiodfromastatedtimeduringwhich,understatedconditions,anitemhasanacceptablefailurerateoruntilanunrepairablefailureoccurs.PerformingTraditionalFunctionsBetterMicroprocessorrelayschemesaresimplerdesignsbecausetheyuselessrelayingcomponentsandauxiliaryequipment.TheseschemesusethesamedatainputswithintherelaytoperformadditionalrelayfunctionsusingBooleanalgebraicexpressions.Theimprovementscanbesummarizedasfollows:Low-burdendevices.Moresimpleprotectionschemesandcompactdesignsduetomultifunctiondevices.Forexample,thetransformerprotectionofprimarydifferentialrelaysandbackuptime-andinstantaneous-overcur-rentrelaysrequiringtenelectromechanicalrelays(EMRs)isreducedtoaprimaryandabackupmultifunctionμP-basedrelay.Lowercost.Widerandcontinuoussettingranges.Greatersensitivityduetohigheraccuracymeteringandrepeatabilityofrelay.Hence,0.2scoordinatingtimeinterval(CTI)insteadofthetypical0.3scanbeusedforcoordination.Faultsensingandhigh-speedtripping,whichprovideimprovedsystemstabilityandpowerquality.Flexibilityfordesigningorchangingaprotectionscheme(notavailablewithsolid-stateanalogordigitalrelays)withoutinstallingadditionalequipmentlikecontrolswitches,becauseofuser-programmablelogic.Negative-sequencepolarization.Negative-sequenceovercurrentanddifferentialelements.Three-polesubcyclecurrent-differentialprotection.Built-insynchronism-checkfunctiontosupervisebreakerclosingconditions.μPrelayscanbetestedunderloadconditionstoconfirmphaseangleandmagnitudevaluesusingthemeteringcommandoftherelay.ProvidingMoreInformationAprotectiverelayingsystemincludesrelays,voltageandcurrenttransformers,circuitbreakers,adcsupply,controlcables,andsometimesacommunicationschanneltoexchangedatabetweenrelays.Hence,protectiverelayingreliabilitydependsonallthesystemelements.Inthepast,EMRswereresponsibleforahighpercentageofprotectionsystemoperationfailuresorundesiredoperations.Asshowninthisarticle,μPrelaysarehighlyreliabledevicesthatprovideprotectionandfaultrecordingandcanmonitorthestatusofsomeoftheelementsoftheprotectionsystem.Theinformationthatthesedevicesgatherduringsystemdisturbancesandfaultsisveryimportantinunderstandingthepowersystembehaviorandevaluatingtheprotectionsystemperformance.Theimportanceofanalyzingthisinformationcannotbeoverstated.Furthermore,manyofthenewfeaturesarenotavailableinprevioustechnologies,suchasthefollowing:multiplesettingsgroupsbuilt-ineventreportingshowsvoltageandcurrentlevelsandrelayelement,contactoutput,andcontactinputstatuseveryone-fourthcycle(forarelaythatprocessesitslogicfourtimesperpowercycle.allrelayeventandSOEinformationforentireplanttimestampedto1-msaccuracy,usingastandardglobalpositioningsystem(GPS)-synchronizedtimesignal,makingpostfaultandinterruptioninvestigationsthatinvolvemultipleeventsindifferentrelayseasytocorrectlyreconstructforrootcauseanalysis.IncreasedReliabilityThefeaturesbuiltintoμPrelaysmakeapowersystemsafer,morereliable,andmoreeconomical.WedesignandtestμPrelaystooperatereliablyinthetoughestenvironments.Afterall,thelessmaintenancearelayrequires,thelesstimetherelayisoutofservice.Out-of-servicerelaysreducetheprotectionofthesystem.ThereliableoperationofμPrelaysensuresthatthesystemisoperatingwithindesignlimits.WithEMRs,theonlywaytoknowiftherelaywasworkingwastoremoveitfromserviceandtestit.Thetestwouldverifyonlywhethertherelayworkedduringtesting.YoucouldnotbesuretheEMRwouldworkwhenyoureturnedittoservice.AnimportantbenefitofaμPrelayistheabilitytoconstantlyrunself-checkstoconfirmthatallfunctionsareoperatingproperly.μPrelayshave75–85%coverageinself-diagnostics,asexplainedfurtherin[5].TheenablelightinfrontofaμPrelayassureselectriciansandoperatorsthattherelayisfunctioningandprotectingthesystem.UnliketheEMRs,whichmaygetcheckedonanannual(orlonger)basis,μPrelayscheckthemselvesthousandsoftimeseachminute.Additionally,iftheselftestfindsananomaly,therelayautomaticallysignalsanalarmconditionthroughfail-safecontacts.Operatorsandelectricianscanthencheckandrepairtheproblembeforeafaultoccurs,especiallywhenthealarmcontactstatusisremotelymonitoredbyacontrolsystem.ReviewofReliabilityMeasurementPracticesReliabilityengineerstypicallyuseoneormoreofthesepracticestomeasureproductreliability.1)Reliabilitypredictionbasedonindividualcomponentfailurerates:Predictionmethodsassumethatallcomponentshaveaconstantfailurerate.Componentfailureratesareaddedtoobtainatotalsystemfailurerate(theinverseofMTBF).TwomethodsareofferedinMIL-HDBK-217,‘‘ReliabilityPredictionofElectronicEquipment’’(1992):thepartscountmethodandthepartsstressmethod.Atotalof19componentcategoriescoverfailureratesderivedfromhistoricaldata;modelsemployempiricallyderivedfactorsthatadjustfortemperature,environment,andqualitylevel.Reliabilitypredictiondoesnotensurethatthereliabilityvalueswillbeachievedandisnotademonstrationofthewaythatapowerconsumptionprediction,beingbasedonphysicallaws,wouldbe.Rather,itisbestusedasabasisforsettingtheobjective,tobeattainedonlyifthereisapersonalcommitmenttoit.2)Productreliabilitytesting:Reliabilitytestingisanessentialpartofengineeringdevelopmenttoaddressrisksanddeterminewhetherdesignsarereliable.Thekeyelementofreliabilitytestingisapplyingstressovertime.Acceleratedtestsmayincludetemperature,temperaturecycling,humidity,andvibration,orcombinationsofthesestresses.Forhighlyreliableproducts,demonstratingthataspecificMTBFgoalisachievedduringproductdevelopmentisdifficultbecauseseveralhundredunityearsoftestingarere-quired.Extrapolatingacceleratedtestresultstonormaluseconditionsiscomplexbecauseofthewidevarietyoffailuremodesandcorrespondingaccelerationfactorsinvolved.3)Observedfieldreliabilityperformance:Reliabilitymonitoringcancontinuebeyondthedevelopmentprocessthroughoutthelifeoftheproduct.LoggingproductshipmentsbyserialnumberandrecordingallwarrantyfailureserviceactionsenablesreliabilityengineerstocalculateobservedMTBFunderfieldconditions.Weuseallthreemeasuresofproductreliabilityatappropriatepointsinourprocess.Reliabilitypredictionmodelsprovideaninitialestimatebasedonproductcomplexityandtypeofcomponents.Weemployhighlyacceleratedlifetesting(HALT)duringthedevelopmentprocesstoforcefailuresandimprovedesigns.Ourno-questions-askedten-year,worldwidewarrantybringsproductsbackforanalysisandrepair.Wemonitorresultsofwarrantyservicetoprovidethefollowing:calculationofobservedreliabilityinthefieldopportunitytodetectunexpectedfailuremechanismsquicklyandinitiatecorrectiveactioninputtoimprovethedesign,process,ormaterialsofcurrentandfutureproducts.ThefollowingsubsectionsexplaintheprobabilisticbutquantitativeunderstandingofμPrelayreliabilitybyobservingμPrelayfailureratesandunavailability.Typically,manufacturerslookedprimarilyathardwarefailuresasthekeyindicationofμPrelayproductreliability.Asweexplaininthefollowingsubsections,andasillustratedinTable1,weusefourqualitymeasurementstomeasureproductqualityandreliability.MeanTimeBetweenFailuresIn1988,westartedrecordingMTBFstatistics.Thisobservedapproachisbetterthanatheoreticalcalculation,suchasMIL-HDBK-217Fpartscountprocedure[6],asitincorporatesmanufacturinganddesignquality.Forrepairableproducts,suchasμPrelays,MTBFinyearsdoesnotindicateusefullifeofasingleunitinyears.TounderstandwhattheMTBFmeasureis,considerthefailurerateisk=0.3333%peryearforaparticularunit.Ifafacilityhad900units,thenwouldexpect900k¼3unitfailuresperyear.Becausetheunit’sMTBFisthereciprocaloffailurerate,theMTBFreliabilityoftheunitwouldbe1/k=300years,or,inotherwords,aMTBFof300years.The300yearsMTBFisausefulreliabilityorqualitymeasurethatisvalidduringtheusefullife(typically,30years)oftheunit.Statedanotherway,foranMTBFof300years,youmightexperienceonefailureperyearduetohardwareormanufacturingprocessforaμPrelaypopulationof300installedunitsforatotalof30totalfailedunitsoverthe30-yearlifeoftheunits.TheMTBFqualitydurationisincreasedbyselectingreliablecomponentsthatarespecifiedforhigh-temperatureoperation,establishingoperatinglimitsofμPrelaycomponentswellbelowthepublishedspecification,designingμPproductsforawideoperatingtemperaturerange(-40℃to+85℃),and,lastly,applyingHALTtoverifyoperatingmarginsandforcefailureswellbeyondnormalspecificationlevelstoimprovereliability.MeanTimeBetweenRemovalsWeintroducedtheMTBRmeasurein1998toincludehardwarefailures(partofMTBF),manufacturingprocesserrors(partofMTBF),firmwareerrors,ornoproblemfoundonareturnedunit.Fora240-yearMTBR,oneofevery240relayscanbeexpectedtohaveadefecteachyear.Figure1showshowproductfailuresoccuroverthelifeofaμPrelay.Atunitreceipt,thecustomerinstallsorteststheunitandmayfindsomeIQerrorsinthefirstfewdaysofuse,whichweconsiderIQerrors.Duringthestablefailureperiod,theproducthasarelativelyconstantfailurerate,mainlybecauseofour100%burn-inoneachproduct,whicheliminatesnearlyalloftheabnormalearly-lifecomponentdefects.Wecalculatetheremovalfailureratebydividingobservedremovalfailuresbythenumberofproductsinservice.TheMTBRisthentheinverseoftheremovalfailurerate.Thetimeatwhichfailureratesstarttorisesignificantlyfromthestablefailurerateregioniscalledthewearoutfailureperiod(seeFigure1).ForμPrelays,thewearoutfailuremechanismisusuallyareductionincapacitanceofaluminumelectrolyticcapacitorsinthepowersupply.Ourunitsaredesignedfora30-yearlife.However,withapowersupplyreplacement,μPrelayscancontinuetofunctionwellbeyond30years.ObservedMTBFandMTBRbasedontheactualreliabilityoffield-installedunitsarebettermeasurements:thecorrelationoflaboratorytestingconditionstofield-useconditionsiseliminatedbyobtainingthemeasurementsfromunitsexperiencingfieldconditions.Inaddition,toobtainsignificantandusefulresultsfromlaboratorytesting,onemusttestalargenumberofunitsforanextendedperiodoftime.Forinstance,todemonstrateafieldreliabilityofa100-yearMTBF,onewouldneedtotest1,000relaysforabout2,000h.Nevertheless,aspartofourdevelopmentprocess,wetestunitsathigh-stressconditionstodetermineanysignificantlife-limitingfailuremodes.Wealsoanalyzeanyfailurestorootcauseandimplementappropriatedesign,material,orprocesscorrectiveactions.Theearly-lifefailuresareconsideredtobethosefailuresthatoccuraftertwodaysbutduringthefirstyearofaunit’sin-servicelife,whereastheusefullifefailuresareconsideredtobethosefailuresthatoccurafterthefirstyearofaunit’sinservicelife.Boththeearlyandusefullifefailures(ordefects)areincludedintheMTBFandMTBRmeasurements.InitialQualityIn2003,weintroducedtheIQmeasurement,whichmeasuresobservedout-of-boxerrorsdetectedbyourcustomersatreceiptorinitialtestingofaunit.Theseerrorsorfailurescanbeduetoincorrectorderentry,performance,configuration,documentation,accessory,orshippingdamage.TheseunitfailuresareincludedintheIQmeasurementbutnotintheMTBFandMTBRmeasurements.OurobservedIQmeasurementforallproductsisapproximately0.6%.MaintenanceIndicatorIn2003,wealsointroducedtheMImeasurement,whichmeasuresMTBRplusallservice-bulletin-relatedupgrades.Wecapturedatageneratedfromdetectedunitconcernsduringinspections,reliabilityandmanufacturingtests,fieldfailurereports,andcustomerfeedback.Oncetheconcernisobservedtobeasignificanttrendandproblematic,weissueaservicebulletintoproactivelyinformcustomersofknownfailuremode(s).AfterlookingatμPrelayusers’experience,weobservedthattheMTBF,MTBR,andIQdonotcapturetheimpactofmaintenanceandservicebulletinsthatareimplementedbycustomerstofixfirmwareorhardwareerrors;hence,weaddedtheMIqualitymeasurement.TheMIqualitymeasurementisamethodofmeasuringcustomermaintenanceactivityandtheimpactofourqualityoncustomers.Thismeasurementisthemoststringentqualitymeasure,becauseitincludesanadditionalerror,thatofproactiveservicebulletinwork(problemhasnotoccurredyet,butmaywithoutintervention),inadditiontoobservedMTBF-andM