Mitigation of Inrush Current in Load Transformer for Series Voltage Sag Compensator

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1 Inrnaonal Journal of Engnrng Rsarch & Tchnology (IJERT) ISSN: Vol. 3 Issu 5, May Mgaon of Inrush Currn n Load Transformr for Srs Volag Sag Compnsaor Asf Hamd Wan M.Tch Scholar, Dp. of Elcrcal Engnrng Loly Profssonal Unrsy, Punjab, Inda Amardp Sngh Vrd Asssan Profssor, Dp. of Elcrcal Engnrng Loly Profssonal Unrsy, Punjab, Inda Absrac In h powr sysm olag bcom h mporan ssu for ndusrs and many ohr consumrs. Accordng o h sury 92% of h nrrupons a ndusral nsallaons ar olag rlad. In arous compans olag may affc many manufacurs and may rduc h ffcncy of h sysm whch rsuls suffcn losss n h powr sysm. Th olag compnsaor, basd on a ransformr coupld wh olag sourc nrr for sral conncon, s among h mos cos-ffc soluon agans olag s. A ransformr nrush may occur a h sar of compnsaor. Ths or currn may damag h nrush procon of h srs conncd nrr and h ransformr oupu olag s graly rducd du h magnc sauraon. Whn h compnsaor rsors h load olag, h flux lnkag wll b drn o h ll of magnc sauraon and sr nrush currn occurs. Ths papr proposs a nw chnqu for mgang h nrush of h couplng ransformr and prsrng h oupu olag for ffc compnsaon. Kywords olag compnsaor, ransformr nrush, olag s, coupld wh VSI may subjc an nrush currn durng h rsoraon of olag. A chnqu o mgang h nrush currn s proposd and mplmnd n h synchronous rfrnc fram compnsaor conrollr. Ths ch. s ngrad wh closd loop conrol on load olag o oban sady sa of olag. By hs chnqu w can succssfully rduc h nrush currn n h load ransformr and robusnss of compnsaor sysm. I INTRODUCTION Volag problm s consdrd on of h mos powr qualy problms, bcaus any powr qualy n n uly may affc h sral knds of sns loads conncd o h powr sysm. Th olag phnomnon s of shor duraon rducon of rms olag causd by powr sysm fauls, araon of load and du o sar of nducon moors ha s nduc loads. Sury rcords show ha shor duraon of rms olag and ransn consu 92% of powr qualy problm. Mosly h olag may affc manufacurs and nroduc losss n h sysm. Th mos common caus of olag s flow of faul currn whch may affc numbr of consumrs. Volag du o h fauls may produc ncorrc opraons n h arous proc dcs. Th olag s a rducon o bwn.1 and.9 n rms olag or currn a a powr frquncy for h m prod 1ms o 1 mn ha s.5 o 3 cycls. Sag may rsul h rducon of ffcncy n h sysm whch ar sns o olag araons. Volag compnsaors bcom h mos cos ffc soluon of olag. Ths olag compnsaors may rsor h whn a quarr cycl. rous closd loop conrol chnqus has bn proposd for olag sourc nrr (VSI) basd compnsaors. Howr n h load ransformr whch s Fg. 1. Sngl ln dagram of h srs olag compnsaor. As shown n fgur 1, h olag compnsaor conss of hr phas olag sourc nrr and couplng load ransformr for sral conncon of h sysm. Th compnsaor s bypassd by h hyrsors whn h grd opras normally for hgh ffcncy. Th olag compnsaor coms no h pcur whn occurs. Th olag compnsaor njcs h rqurd olag hrough h load ransformr whch s srs n h sysm o proc h sns load ffcd by h. Bfor h olag rsoraon h dformng olag nsd h load ransformr may caus magnc flux daon and magnc sauraon may asly occur hs rsuls h nrush h ransformr. Ths nrush may damag h or currn procon of h VSI and lad o falur of compnsaor. Ths papr prsns h nrush mgaon chnqu by h flux lnkag offs of load ransformr and h chnqu wll b ngrad wh fdback conrollr of compnsaor. II CONFIGURATION OF COMPENSATOR Th pr phas qualn crcu of h compnsaor ar shown n fgur 2. Th oupu of h nrr s flrd by IJERTV3IS

2 Inrnaonal Journal of Engnrng Rsarch & Tchnology (IJERT) ISSN: Vol. 3 Issu 5, May low pass flr ha s nducor of ransformr L f and capacor C f whch supprss h dc componn and PWM rppls from h oupu of nrr olag m. Fg. 2. Pr phas qualn crcu of h compnsaor Equaon (1) and (2) ar h dynamc quaons of h qualn crcu: synchronzaon of a gnraor rmans ou of phas, oudoor fauls and fauls rnoaon. Th nrgzaon of a ransformr produc o h smpls suaon of nrush currn and h flux n h cor may xn a maxmum horcal sgnfcanc of wo o hr ms h aluad flux pak. Fg. 3 dmonsras how flux lnkag and currn changs. Thr s no sragh sgn ha h nrgzaon of a ransformr can produc an abrup falur du o hgh nrush currns. Though, nsulaon falurs n powr ransformrs whch ar rpadly nrgzd undr no load suaon suppors h msrus ha nrush currn ha a dangrous rsuls. Th ransformr nrush currn s h funcon of sral approachs lk h rmnal olag swchng angl, h rmanng flux of h magnc cor, dsgn of h ransformr, mpdanc of h sysm c. ma ma ca d L f mb mb cb d mc mc cc (1) ca ma La d C f cb mb d cc mc Lc Whr [ ma mb mc ] T s h nrr oupu olag, [ ma mb mc ] T s h flr nducor currn, [ ca cb cc ] T s h compnsaon olag, and [ La Lc ] T s h load currn. Equaon (1) and (2) ar ransfrrd no h synchronous rfrnc fram as (3) and (4). (2) Fg. 3. Inrush currn formaon d mq mq 1 mq 1 cq d md md Lf mq Lf cd d cq cq 1 mq 1 Lq d cd cd C f mq C f Ld Whr suprscrp ndcas h synchronous rfrnc fram rprsnaon of hs arabl and ω s h angular frquncy of h uly grd. Equaon (3) and (4) show h cross-couplng rms bwn compnsaon olag and flr nducor currn. III INRUSH CURRENT STUDY Whn a olag s subjcd o a ransformr a a prod whn normal sady-sa flux would b a a dffrn alu from ha rmanng n h ransformr, a currn ransn happns, known as magnzng nrush currn. Th sauraon of h magnc cor of a ransformr s h ky sourc of an nrush currn ransn. Th sauraon of h cor s owng o an suddn araon n h sysm olag whch can b producd by swchng ransns, (3) (4) Th gnral quaon ha gs h amplud of nrush currn as a funcon of m can b xprssd as: ( ) 2V m () Kw Ks(sn( ) sn ) (5) z Whr V m s maxmum funconal olag; Z s oal mpdanc undr nrush, as wll as sysm; φ s nrgzaon angl; s m; s a pon a whch cor sauras; τ s a m consan of ransformr wndng undr nrush crcumsancs; α s a funcon of ; K w xplanaons for 3 phas wndng conncon; K s xplanaons for shor-crcu powr of nwork. A basc quaon can b usd o analyss h pak alu of h frs cycl of h nrush currn. Ths quaon s as follow: pak 2V m 2. BN BR BS ( ) 2 2 (.L) R BN (6) IJERTV3IS

3 Inrnaonal Journal of Engnrng Rsarch & Tchnology (IJERT) ISSN: Vol. 3 Issu 5, May Whr V m maxmum appld olag; L ar cor nducanc of h ransformr; R oal dc rssanc of h ransformr; B N sandard rad flux dnsy of h ransformr cor; B R rmnan flux dnsy of h ransformr cor; B S sauraon flux dnsy of h cor maral. As sn from h quaons (5) and (6), h charg of nrush currn s dpndn o h paramrs of ransformr and oprang crcumsancs. So a full analyss for rsulng h rlaons bwn h nrush currn characrscs and hs facors ar ndd. IV METHODS USED FOR CONTROL Th proposd conrol mhod s shown n a block dagram n whch d axs conrollr s no shown for your smplcy. In h block dagram full sa fdback conrollr wh nrush currn chnqu ar usd. Dald xplanaon ar gn as bllow: A. Th Full Sa Fdback Schm Th sa fdback schm conans fdforward conrol, fdback conrol, and h dcouplng conrol. 1) Fdback Conrol Th fdback conrol s usd o mpro h accuracy of h compnsaon olag, h robusnss and h dsrbuon rjcon ably agans h araon n h paramrs as shown n block dagram. Th olag from h capacor cq s. h nnr loop olag conrol and h currn from h nducor mq s h currn conrol n h nnr loop Th conrol of h olag con b don by h proposonal rgulaor wh olag command cq rspcly accordng o h rqurmn of h. 2) Fdforward Conrol Fdforward conrol s addd o h olag conrol loop for nhancng h dynamc rspons of h olag compnsaor and o compnsa h olag whou makng any furhr dlay. Th fdforward olag command can b masurd by jonng h compnsaon olag and h olag drop across h flr nducor whch s producd by h flr capacor currn. 3) Dcouplng Conrol In h block dagram h cross couplng rms and h dcouplng rms s drd from h synchronous rfrnc fram ransformaon and h xrnal dsurbanc n h olag compnsaor. Ths conrols ar usd o nhanc h prcsnss and h dsrbuon ably. Ths rms can b oband by calculang h flr capacor olag, load currn and h flr nducor currn. Fg.4. Block dagram of h proposd nrush currn mgaon chnqu wh h fdback conrol IJERTV3IS

4 Inrnaonal Journal of Engnrng Rsarch & Tchnology (IJERT) ISSN: Vol. 3 Issu 5, May B. Th Full Sa Fback Schm 1) Flux Lnkag Dc Offs By ngrang h ln olag, w can masur h flux lnkag of h ransformr as gn n quaon 7. Fgur 6 shows dla/wy hr phas ransformr hang sngl wndngs and s nsalld n downsram of olag compnsaor. Th lnkag of h flux n h phas a-b wndngs s xprssd as: () (7) ()d Fg. 7 shows h ln-o-ln olag hrough h ransformr wndng and h causng flux lnkag aand from h olag ncdnc o complon of olag compnsaon. Whn olag s happns (= ), h conrollr snss h gd olag and nsrs h ssnal compnsaon olag a = dc. Th flux lnkag hrough h olag compnsaon procdur can b drc as followng: Fg. 6. Conncon dagram of h proposd sysm and dla/wy load ransformr. d c () () ()d ()d (8) d c Fg. 7. Transformr olag and corrspondng ransn flux lnkag Abo quaon can b rwrn as follows: Fg. 5. Phasor dagrams of arous yps of olags s () () ()d dc ( () ())d ()d (9) IJERTV3IS

5 Inrnaonal Journal of Engnrng Rsarch & Tchnology (IJERT) ISSN: Vol. 3 Issu 5, May Whr V () s h pr-faul load olag dfnd as follows: Ths dynamcs of h ransformr qualn crcu n Fg. 8 can b xprssd as: ^ () V sn( ) Whr Ṽ s h magnud of load olag, ω s h grd frquncy, and Φ s h phas angl. Thus, afr h olag compnsaon s compld, h flux lnkag can b xprssd as follows: ^ V () () sn( ) dc (1) 2 () () dc dc ( () ())d dc (11) By h abo quaon no. 11 h flux lnkag DC offs Δλ whch s oband by h olag s on h ransformr wndngs, also h flux magnud s dpndn on h dph and h duraon of s. rous olag s may occur h DC offs whch can saura h cor of h ransformr abo h kn may caus nrush currn. Usually h magnc sauraon kn s p.u. of sa-sudy flux lnkag. 2) Dsgn h Flux Lnkag Esmaon Th sngl phas ransformr undr no load condon s shown n fgur 8, whr R 1 and L l1 s h prmary sd qualn rssor of coppr loss and h qualn lakag nducanc rspcly. R c and L m s h qualn rssor of cor loss and magnc nducanc. Fg. 8. Equaln pr phas crcu modl of h ransformr La La La d L R m 1 d Lc Lc Lc (12) No ha for smplfcaon h lakag nducancs and h cor losss ar nglcd. Ths quaon can b r-wrn as: Whr La La La d R1 d L m Lc Lc Lc Whr T L La Lc m La Lc (13) Th dynamcs of h ransformr flux lnkags can b ransformd no h synchronous rfrnc fram as: Lq Lq Lq Lq ( ) d Ld Ld Ld Ld (14) Whr h dampng rao, ζ=r 1 /L m, chooss h ransn of h flux lnkag. Fgur 9 llusraons h flux lnkag smaor undr h synchronous rfrnc fram rsulng from h quaon (14). Th flux lnkag smaor, as prsnd n Fg. 9, s appld h proposd nrush mgaon chnqu. Th proposd nrush mgaon chnqu conans fdback conrol and fdforward conrol. In h fdback conrol loop, h flux lnkag λ Lq s producd by ngrang h load olag Lq. Th abnormaly of h flux lnkag can b nndd by h dffrnc bwn λ Lq and h flux lnkag λ Lq. Th rror s conrolld by a proporonal-ngral (PI) rgulaor. IJERTV3IS

6 olag flux currn olag Inrnaonal Journal of Engnrng Rsarch & Tchnology (IJERT) ISSN: Vol. 3 Issu 5, May Fg. 9. Th flux lnkag smaor undr h synchronous rfrnc fram. To spd up h dynamcs rspons of h nrush currn mgaon, h rror bwn h projcd flux lnkag DC offs and h flux lnkag command ( λ Lq. = λ Lq - λ Lq) s appld as a fdforward conrol rm. Th command s mulpld by a proporonal gan K p (=1/ T) o fas-rack h DC offs compnsaon hroughou h compnsaor sar ransn. Th conrol gan K p s dsgnad accordng o h accpng of nrush currn and h m oblgaon of flux lnkag DC offs compnsaon. Th summaon λq of fdback and fdforward command s addd o h compnsaon olag command mq o cra h compl command olag of h olag compnsaor. Thus, h projcd conrol mhod ndca h olag compnsaor o ach an ousandng load olag rackng and aod h nrush currn happns on h load-sd ransformr. V SIMULATION RESULTS m Load Volag V l m Ib Ic Ia A. Whou Inrush Mgaon Tchnqu. Load Currn I l m Sourc Volag V s 2.5 x m Transformr flux lnkag λ l b c a IJERTV3IS

7 flux currn olag Inrnaonal Journal of Engnrng Rsarch & Tchnology (IJERT) ISSN: Vol. 3 Issu 5, May B. Wh Inrush Mgaon Tchnqu. VI CONCLUSION m Sourc Volag V s m x Load Currn I l m Transformr flux lnkag λ l Ib Ic Ia In hs papr a chnqu usd for mgaon of ransformr nrush currn ncludng wh full sa fdback conrollr o lmna h nrush currn ffc a h m of olag rsoraon n h powr sysm. Th conrollr prods o conrol h olag, h currn and h flux lnkag. Th mhod usd for conrollr s basd on h synchronous rfrnc fram whch allows h compnsaor o njc h olag ry quckly and prns h nrush currn for sns loads. Whn h olag happns, h conrollr calculas h ransn flux lnkag on h bass of pr faul olag and calculas h rqurd olag n ral m for fas compnsaon and lmnaon of flux lnkag dc offs crad by olag. Th chnqu usd for rmoal of olag and h nrush currn s shown n h smulaon rsuls. Th projcd chnqu can also b jond wh h nrush rducon chnqu of h couplng ransformr obanabl by h smulaon rsuls dsplay ha hs wo approachs ak rsul a dffrn sps of h olag njcon whou nrfrng ach ohr. Th combnaon of hs wo approachs confrms a fas and prfc olag compnsaon wh mnmum dangr of nrush currn. REFERENCES 1. C. J. Huang, S. J. Huang F. S. Pa, dsgn of dynamc olag rsorr wh dsrbuon nhancmn, IEEE Transacon on powr Elcroncs, ol. 18, pp , sp N. H. Woodly, Fld xprnc wh dynamc olag rsorr (DVRTMMV) sysms, n Proc. IEEE Powr Eng. Soc. Wnr Mng, Jan , 2, ol. 4, pp J. G. Nlsn and F. Blaabjrg, A dald comparson of sysm opologs for dynamc olag rsorrs, IEEE Trans. Ind. Appl., ol. 41, no. 5, pp , Sp.-Oc P. T. Chng, C. L. N, J. M. Chn, Dsgn of a sa fdback conrollr for srs olag compnsaors, Powr Conrson Confrnc, pp , Aprl L. Yun W, F. Blaabjrg, D. M. Vlahgamuwa, and A. P. C. L. Poh Chang Loh, "Dsgn and Comparson of Hgh Prformanc Saonary Fram Conrollrs for DVR Implmnaon," Powr Elcroncs, IEEE Transacons on, ol. 22, pp , Yu-Hsng Chn, Chang-Y Ln, Jhao-Mng Chn, Po-Ta Chng, An Inrush Mgaon Tchnqu of Load Transformrs for h Srs Volag Sag Compnsaor, IEEE Transacons on powr lcroncs, ol. 25, no. 8, augus P.T. Chng; C. -C. Huang; C. C. Pan; S. Bhaacharya, Dsgn and mplmnaon of a srs olag compnsaor undr praccal uly condons, IEEE Trans. Ind. Applcan., Vol. 39, pp , May-Jun P. T. Chng, W. T. Chn, Y. H. Chn, C. L. N, and J. Ln, A ransformr nrush mgaon mhod for srs Volag compnsaors, IEEE Trans. Powr Elcron. ol. 22, no. 5, pp , Sp W. Xu, S. G. Abdul Salam, Y. Cu, and X. Lu, A squnal phas nrgzaon chnqu for ransformr nrush currn rducon, Par II: Thorcal analyss and dsgn gud, IEEE Trans. Powr Dl., ol. 2, no. 2, pp , Apr C. N. M. Ho, H. S. H. Chung, and K. T. K. Au, Dsgn and mplmnaon of a fas dynamc conrol schm for capacorsuppord dynamc olag rsorrs, IEEE Trans. Powr Elcron., ol. 23, no. 1, pp , Jan M. S. J. Asghar, Elmnaon of nrush currn of ransformrs and dsrbuon lns, n Proc. IEEE Powr Elcron., Drs Enrgy Sys. Ind. Growh, 1996, ol. 2, pp IJERTV3IS

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