A High-Accuracy Optical Current Transducer for Electric Power Systems

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  8  Transction  Pwer Devery, Vl. 5 N2 Apl 1990   GCCUY  RE UR FOR ELEC POR SYSMS Ear A lm J Mb Suare D - lgn Industes C  F  ABSAC  Ths paper epors fo he fst e on a optil cunt  trasduc plyg a ew sp tchiqe to measue letrc cen h technique is based n a fudaenta anayss f he Faraday c An pcal crent transducer OC has ben designed whch ovcos he distubing eecs o tepraue on h glass sensg elemt y aligning th rasmsson ais of th poaizer a a specc angles the OCs uput is show t be ndependt f  tempar. High accuacy measnts a herby possibe v a wide rang of tepaturs Two pac OCT dsgns or xahigh votage powr sysms a cpared Ky Wods: elec cur easun opical snso araday  ec, birerignce 0 INODCTION uing the as w ddes any gops condcd resarch on hw to us optl echues to ar elecc cun []  he pray objctive of a larg ajoriy o ths goups was  t develop an opl cur transdcer (OC for lecic utlis Figes  and  iustrae typca senso conguratons. Optl technius pacualy ber opts oered ceain basic adantages o the uis (1) spler more relble hgh voage nsuaors on their crnt snsors; 2 otal eectrl soation bewen h snsing scue and th sbstatio conol oom (3 eec ouput sgnals or copable wh  he coputer based euipent croig oday's and  tmorrows power systs and (4) accrae cuent masume ove a ve wd dynaic rang of cents  he reseach wk, however, poved dcu Neay a the optl sches to sue curnt use th Faaday eec the rotaon of the plan of polaraon o polarzd light propagating n a agnc field igh passes  hrgh gass snsing mens cls  he powerin Faday rtaon is pduced by the magneic d ceated by  he 60 curr n th pwne sing wo polazes set at   to each her the 0Hz Faaday rotaon is conveed o a 60Hz intesty odulatio o h lgh < n ] PWRD A pper -  'comnd and Pprove by   w Syst Iunai & �f( !t_'ns C  il  w gil  for [ t he /S H TL  b  p   7, 198q.  sumd cb 4 gB;  valh f  Fbu 14, q  he Faraday ec n dagnetic gasses s dpndnt o  teperatr. his indpendnc is a a advantag or sensors whos ial teperars n range om -50 C to +10·C. Howver evn small emperare cangs pdc stress n the gass sensng elemens The indx of refracn Is no lnger srpic The nonuno index f refacon is  ted brengce Sess-duced biengence cased by mpatue chags dstos the pane polard ight cvtig   o llptical polariation, and podcing an nwaned change in h innsiy f  the optca sgnal he princpa pbem plagng resachs in th last dcad has bn how o vrcome he ffecs of biengence used by teperar changs 811,13 Ths paper descbes a nw sple qe soluon o hs key pb a suon ha permits a practical opl curren ansduc to be consuced hat pvds hgh accuracy measues vr a vy wid rag of  tempeatures SENSOR  ASSEMBLY OPTIC INFE UN Fg  he principal ens of an optical crrent  tansduc are th snso assbly the dctrc  fber-opc cabe and he optcal nterfac u h ectronic contos) 2.0 NA SCITON g. 2 shows th basic cmponts  an OC. hes sensors reure (1) a light source hat is usally an infraed L copable wth optil fbers, 2) all dileric optial fbers t  ans th lgh to an fro th sensor had (3 an a-opca 8-897/90/0189$0100 © 1   enor hed with no ovng pr nd o eeroni 4)   oi hghvotge inutor with o o o 6 g nd (5)  photo-etetion nd gnl proeg elcroic h deet  the re gn   CONCENTRAOR �) POW LIN POLAIZER  ANALYZER O o b FARADAY, GLASS NG O �   GASS -i '�  \ U .W �  ANALYZ POLAIZER � HIG ; VOLTAGE-  : INSULAO Fig 2 feren optil deg n be ployed n opl rent eor:   deig ig   mgnetield onettor with  inge pee of  g, d b  rg-deg whee the light ele  the power le    82n D provde  ont inenity light oe Wth  no en in he power lne  potion of he lght pe  through he entre yte nd proue  tedy d level in  the  eetion eetron. A 6 en then produe   6Hz  moduton of th d eve  The Frdy effet in dignet ge  we noted elier,   idependnt of tpertre. Howevr the Frdy efect  depend rher togly on the wveength of the lght ued i  the ye []. o fi the wvelengh of the  we ue   eperure ontro ye  indted in Fig 2 Optil ber tnit the ght o nd fro the eor hed.  he er re g nd ffod opete eetril iolio  beween the eno he nd the eeton ontrol goe tende e with high nerc pere re bet  u thy re eier to wo wth nd ptre  gfit  oun of gh Oe peil requireet of the fber i ht  they e impeiou o wter mgro beween he ldg  nd he protetive bu mter I  of oe, peive  tht moitre no petrte he hghvoltge nto Beue he ony thg ide he high voltge nto e wo optl fie the nltor c e ve th uheoe  the voltge te on the nuto wll e h oe nifo ompred to the ed te n  onvention CT.  The optil eemen n he eno hed re diued in more  detil in the followig etion. One he ight et to the optc inefe un the  eleto peo three functon  photodetetio d  mpiion uig  ion photodeteo nd   trnimpedne pier; (2 g proeg (diued  tr nd (3 ouput mplier whih ree ppropte opt gn One of the o ipot fetre of hee enor   the bity o provde y deent pe of eleton oupu fom  ige enor hed he fmlir onep of  brden dipper Adding eetroni d tht povde ore oupu ign doe o degde the othe outpu ig.  3 TORY I  ul to develop the theo of o new OCT y   riing n ection 3. elow he b theo of the rdy  efet n how  h een pplied o optl ren  nder. Ne in 3.2 we expnd on thi ple theo o  nlude expliity the eet of birefringee. Pevo method  fo overog the nwnted ee of ierngece re  preented n 3.3 Fny i eon 3 we expli our nw  ipled ethod  31 Gener  . )  derbe in iple fo he ottion of polred gh by  the y eet 9=VH )  whee 9 the gulr otton of he plne of poltio   the  permbit of the e V he Verdet ontnt  the  mgne ld itenty, n L  the pth lgth n the gl over  whih he eld ne with the lgh. (A  go of yol  i provided n ection 7. he Verdet onnt for  gve  894 maea describes the magtude of he Faaday eect as te oato pe uni ed pe ut legh. Te exac eatosp bewe e magetic fied ad e eeic cuent, I wll deped o the geome ad we a we  9   V KI  2  whee  s a geome-depende costant. A descipto suc as Eq. 2 apples to the OC desig iustaed  g  2a whee te magc d coceato povids a eatvey uiom mageic fed tougout the Faaday sesg eemet o O desigs usated  Fg 2b whee the gt makes a compee u aoud he coduco:  9   V f H· dL  whch hough Ampee's cuil aw educes o   / V I N  wee N s the numbe of us aound he coducto Fig 3 he thee key opl eemens  the seso hd of a opia cuent aduce 3 4 ig 3 lustates a typil Faday seso wth te asmsson  aes of the poaze ad aaze at 45 s eads to a modulaio o the esy of the gh popagatg ough the sys he nesy  D  at he potodeecto s  D  ( r d  2 (1  s 29 5  Siga pocessg eetonics dvdes the ac compoet of Eq 5 o SIN 9 by te dc compoe o/ o elimiate e depedece on gh te y he esug opt siga s m=s 2 A he siga pocessg eectocs tha combe Eq 2 ad A o poduce a ac ouput siga diecy popooa to e pima cuen in he pow e o a cocetato-based O s - m 1  58  ad fo a ngdesg O s - m 1  5C  V N Rembe, m s the measued quaiy ad te othe tes ae costats Aaog pocessing ccuts ceate a oupu decly popoioa o the powe e cuet ad i pase w tat cuet Ufounatey he wo smpe equaios 5)  ad A do o,  gea descbe e ea wod  32 Biefge aaday Maa  e uatos above ae aduate beause they do not  accout o the dstog efecs of befngece o the lght.  he seina pap teatg te  aaday efect in a befgent meda was we by abo ad Che [10] Usg he otaio o Day et a 6] we pevious deveoped ths heo of a bfget aday matera ad apped  to op cuent  asduces . A 2  X  2 mat emen s used in Eq 6 to descibe gh popagag  a berigen aaday maea ] (EXO)  f COS ;2 si;    2 2 /;)Sin 92 l E  E y l x  E y  2 F/;)Sn 2) cos /2  j(/)n L/2 L 6  whe  E o  s te gt eec ed amplude o t � e ghwave   s te pah gt  te Faaday maal    e aaday oato p u eg  s he biegece pe un gh  ;  s a coaio of ad  gve by  ;     F  6A  wh 68   s he nge the polze's rnsmisson axs kes wh he chcesc direcion n  he Faday aeal and  s he angle he anayz kes wh h se chraesc decton. (See g 4 A key p of his eale wo ws o ntodce s vbes  these ngles ha the polize nd nyze ansmsson xes ae wth  chtesc decion The esuig expesson   he eecc ied apde of he gh tnsmed hrgh he syse s: (F/sn(sn)] j  snos(+I] (6C Mlplyng (6C by s conjgae, we deved []  he gene expesson lgh inensy,    nsied though the op syste stred n g. 4: oI,  {cos·(L)cos(  )  (4  ' sin Lsin (-a) + (6 Noe the copexy o Eq (6 he pree  s  non o boh the bengence p nd he ady eec,  heoe c s boh n gu o nd coe o he snsodl fncons. Yet hs meased lght nensy mst  sed to uaey detemne  even hogh p y be chngng. 33 Mehods o Elnaing he Efets of Bengence eos eserchs [Hl 3] hve ecognzed he dles posed by bfngence Jaekn 1 sggesed creng  specc ellpl polizaion se o he lgh enteng he Fdy ael I s no ceain ha hs  hnqe couned o vriaons n brengence; fo exple  varaton podced by empeae chages He so poposed ctng he aady ae ong one piece  nd ctng  back ogehe Ths sees pcc heoe he at o cung the ae n se nodce sgnn n sess befngence Rshlegh nd Ulch [3  wee the s to propose wstng the op b o those OCTs consced wih oops o sngede opl be he ws-ndced c biengence swps o the n sess befngence oweve the elsoopc coeffient ssoced wh the ws s emperue dependen Si oth nveno hve ed echana eedback syses o copense o he beringence [3] n o eie wo [ using the ndenl eqons  epodced bove we wee be o cte n OC h had no ovng ps nd one h fnconed we, en wh chnges n the bengence, and heoe opeed ov  wde nge o pee We densed ha by setng he pozer  tnssson s   a=.5 nd sng  bsplng nayzer  tgve two oup sgns  =a:4  we ld wih soe clng detene the bengence Once the bengence  ws known  econ o ws developed ae ore clng hs coeon fo ws pped o one o he op sgnas o podce  ady on sign ee of he disbing ees o bengence Whe hs ehod nctonal qte wel i eqired eensve lclons on  cocompe pus  toa o hee opl bes between he senso hd nd he eeconc conos  beaspng anlyze and wo phoodetecto peper/sgnpocessng stges n the eeoncs 34 poved Mehod O n ethod bns ppopely wh the undamena eaon Eq (6) dcbng dy oon n  bengen ed HRTISI DIRIN \/' ,. P  g 4 The ec eae o ady oton n  bfngen aals eqes  eaen bsed on a chaactersc deon n the tea The chesc drecn s eqvalent o a pncipa xs n css) he xes o he pole nd ner e dened wh espec o ths chactesc deon   wh os dy senso we oen the por and nyz t   to ch othe so (l)  45  As befoe we dvde he c ponen o he sgna by the dc copon o eove ny dependence on he gh source nsy We denote hs as o (c = 6  (d Reeb chnges n epae podce chges n the bengce nd he ssos op sgn vs e n lse hese chnges by lcng te OC sgnl,  usn Eqs (2 6) (6A) (6) (6) nd 7). he dependence of he
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