INVESTIGATION OF THE OPTIMUM LINE RECLOSING TIME FOR INTERAREA OSCILLATION SUPPRESSION

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1 INETIGATION OF THE OPTIMUM LINE RECLOING TIME FOR INTERAREA OCILLATION UPPREION K. W. Chn G. W. Ci T.. Chung G. Mu Deprtment of Eletril Engineering The Hong Kong Polytehni Univerity Hung Hom, Hong Kong AR, PRC Deprtment of Eletril Engineering Northet Chin Intitute of Eletril Power Engineering Jilin, P.R.Chin Atrt The pper preent new pproh to dptive optimiztion of utomti line reloing time t trnient fult for enhnement of power ytem trnient tility. It i ed on the tudy on the feture of trnient energy ro networ. The trtegy i derived from minimize lol networ trnient energy the optimiztion trget nd ould e dptive to ytem operting ondition nd fult ondition, nd h een vlidted on oth ingle nd multi-mhine ytem. Keyword: Trnient tility, Automti Line Reloure, Inter-re Oilltion, Topologil Trnient Energy 1 INTRODUCTION With the rpid growth of lrge interonneted power ytem, there i n urgent need for inter-re trnient tility emergeny ontrol to void ny ttrophi reult. Automti line reloing heme pplied in the extr-high-voltge inter-re trnmiion ytem i one of eonomil nd effetive men for mintining trnient tility nd ynhronim [1]. It i eue mot of trnmiion line fult (6-8%) re of trnitory nture [2], utomti line reloing i often le to ler fult nd retore ervie. Reent tudie hve hown tht there i n optiml reloure time for given ytem opertion nd fult ondition. It i lo well nown tht the fixed time intervl reloure tehnique widely dopted in extr-highvoltge (EH) trnmiion ytem n poe prolem [3]. Conequently, invetigtion of the effet of line reloure on power ytem tility nd the dptive etting of optiml reloing time h ttrted oniderly ttention nd eome n ppeling re for mny reerher. Generlly, three iue hould e onidered in the implementtion of utomti line reloure tehnique for enhning trnient tility. () Firt, the fult type (trnient or permnent) hould firt e identified [3,4]. () eond, the optiml reloure heme hould e effetive nd imple to implement with it etting dptive to the previling ytem fult nd opertion ondition. () Third, predition of ytem dynmi vrile re required eue there will e time dely from the iue of the reloure ommnd to the reer withing. Among thee, the priniple of etting of the optiml reloure time for the enefit of trnient tility will e onidered in thi pper. It i ommon undertnding tht fter line reloing will improve firt wing tility. In ome e, however, fter line reloing my not improve the trnient tility, nd leving the line opened my e even etter thn reloing it [5]. By onidering ingle mhine nd infinite u ytem, the optiml reloing time i elieved the intnt t whih the ngle i equl to the pre-fult equilirium point. The trnient energy funtion (TEF) with repet to COI frme h lo een pplied to determine the optiml reloing time y minimizing the trnient energy of potreloure power ytem. It, however, h the prolem tht the determintion of the COI frme require the meurement nd trnmiion of the rotor ngle of ll genertor in ytem, whih i lmot poile in lrge power ytem [6,7]. Let u onider upon the removl of fult, trnient energy i ineted into the power ytem nd tored in the genertor rotor lled the ineti energy, nd it will e onverted into potentil energy ditriuted over the networ. If the ineti energy n e fully ored y the networ, ytem will remin tle; otherwie, the ytem will eome untle. Thi men tht the ditriution feture of the potentil energy over the networ my reflet the trnient performne. In the pper, the ditriution feture of the potentil energy i exmined ed on the topologil energy funtion of multimhine power ytem. The mehnim on how the trnient energy ould trengthen lol etion of networ ut deteriorte the ytem tility i fully tudied o to develop new method for the eletion of the optimum reloing time. 2 POWER YTEM MODEL For the power ytem with m mhine nd n ue onneted y l trnmiion line. The networ i ugmented with m fititiou ue repreenting the genertor internl ue, in ordne with lil mhine nd frequeny dependent lod model, nd negligile dmping. The totl numer of line nd ue in n ugmented networ re therefore l=l +m nd n=n +m, repetively.

2 Let δ i e the i th u phe ngle with repet to ynhronouly rotting referene frme nd the u frequeny devition i given y ω th i = δ i. With the n u the referene u, the lod ngle n e ten αi = δ i δ n, nd line phe ngle differene = δi δ. It i nown tht if dmping i negleted nd (α,) i the tle pot-fult equilirium point, the topologil Lypunov funtion n e deried follow [8,9]: 1 T ( α, ωg) = ωgm g ωg + W( α, α ) 2 = ( ω ) + ( α, α ) KE g PE where Mg i digonl mtrix of mhine inerti, α g i vetor of mhine lod ngle, ω g i vetor of mhine frequenie, T g i onnetivity mtrix, P i vetor of line rel power flow orreponding to pot-fult tle equilirium tte. The potentil energy n e expreed follow : ( αα, ) = [ g( u) g( )] T du PE l = [ P ( u) P ] du = 1 where i the th th line ngle differene, i the ngle differene orreponding to pot-fult tle equilirium tte, P ( ) i the rel power flow in th line, nd P ( ) i the th line rel power flow orreponding to the pot-fult tle equilirium tte. Now differentiting ( α, ω ) long the tretorie g of n give: ( α, ω ) (3) g Eqution nd (3) illutrte tht the totl power ytem trnient energy (i.e. the um of ineti energy nd potentil energy) will e eep ontnt. The ineti energy my e interpreted the um of ineti energy of individul genertor, nd the potentil energy my e identified with individul trnmiion line (inluding genertor trnient retne). For n ritrry line, the th line potentil energy i given y : ( ) = [ P( u) P )] du (4) PE If i denoted vlue of (t) t firt lering time nd PE ( ) i referred th line potentil energy, the repreenttion of the th line potentil energy long pot-fult tretory with repet to pot-fult ould e trnformed into [6] : PE ( ) = [ P( ) )] (, ) u P du+ PE (5) where PE (, ) i the differene of th line potentil energy etween the ngle nd. In e only the pot-fult trnient performne i onidered, PE ( ) n e ten the th line potentil energy referene. A reult, the th line potentil energy long pot-fult tretory fter the firt lering time ould e formulted : PE ( ) = [ P( ) )] u P du (6) i.e. the line potentil energy n eily e omputed from the line power flow nd ngle differene. 3 DITRIBUTING FEATURE OF THE POTENTIAL ENERGY OER NETWORK Firt, let onider the one mhine infinite u (OMIB) ytem hown in Figure 1 nd invetigte the feture of line potentil energy ditriuted over the networ. G ~ f Figure 1: One mhine infinite u (OMIB) ytem The power trnferred from the genertor G to the infinite u i funtion of ngulr eprtion δ etween the rotor of the genertor nd infinite u. Thi ngulr eprtion i due to four omponent: genertor internl ngle G 1, nd three line ngle differene 1 2, 2 3 nd 3. Trnient energy(p.u) Trnient energy(p.u) totl PEG 1 PE1 2 KE PE Time in eond () tle e KE PE2 3 totl Time in eond () untle e PE 3 PE 3 PE1 2 PEG 1 Figure 2: Plot of ineti energy nd potentil energy

3 Figure 2 how the effet of three-phe fult ourred t one of line etween u 2 nd 3. Thi fult w lered y tripping the fulty line out. The ineti energy nd line potentil energie re plotted in Figure 2 () nd (), orreponding to tle nd untle ytem, repetively. By exmining the trnient energy omponent hown in Figure 2, it i oviou tht the totl trnient energy of power ytem i ontnt depite whether the pot-fult power ytem i tle or not. The ineti energy i grdully onverted into the totl potentil energy, whih i the um of the potentil energie of the eh line (inluding genertor trnient retne). Now let exmine the tle e depited y Figure 2(). When the fult i lered y iolting the fulty iruit from the ytem, the eletri output exeed the mehnil input nd ue the rotor to deelerte. A reult, the ineti energy gined tend to drop, nd menwhile the potentil energy egin to inree ordingly. A the ineti energy eome zero when the genertor peed i equl to the ynhronou peedω, the totl potentil energy (whih i the um of totl line potentil energie) rehe it mximum. Thi i evident from the plot of line potentil energie in Figure 2(). PE / totl G Fult lering time in eond Figure 3: Line potentil energie v mximum ineti energy Among ll the line, the potentil energy of line 2-3 i the highet. When the rtio of the potentil energy of line 2-3 to the mximum ineti energy i onidered, the rtio inree with the fult lering time inreed hown in Figure 3. Thi indite tht, the ytem tility deteriorte, more ineti energy will inet into the ytem nd mority of it will e onverted into the line potentil energy of ertin utet (i.e. lol trnmiion etion). If thi utet ould er the inreed potentil energy, the ytem will remin tle; otherwie, thi extr energy would led to lo of ynhronim nd the ytem will eome untle with the networ eing tered prt long the utet. Figure 2() how the trnient energie of n untle e. The ineti energy gined during the fult h exeeded the potentil energy oring pility of the pot-fult ytem (the ritil trnient energy). A reult, the ineti energy long the pot-fult tretory ontinue to inree with the genertor peed nd ngle inreed ontinuouly. A the totl trnient energy remin ontnt, the totl potentil energy would drop ontinuouly. Among the four line, the potentil energy of line2-3 deree ontinuouly while the other vry within mll rnge. Line phne differene O G Time in eond Figure 4: The urve of line potentil energie Figure 4 illutrte the phe ngle differene of eh line. In le thn 2 eond, the ngle differene of line 2-3 h inreed over 18, ompred with the other line where the line ngle differene only vried within limited rnge. Thi indite tht the networ h een torn prt into the two prt long the utet {2-3}. One i the u group {G,1,2}, whilt the other i the u group {3,}. In other word, intility detetion nd torn line identifition n e eily done uing the line potentil energy. In ummry, it n e onluded the power ytem trnient performne i loely oited with the ditriution feture of potentil energy. 4 CAPTURE OF OPTIMAL RECLOING TIME Figure 5 how n inter-re power ytem. A the hnge of eletri networ topology ued y tripping nd reloing of trnmiion line will hve lrge impt on the ditriution of trnient energy over the networ, the tripping of tie-line will hve impt on the other line. In order to gretly improve the trnient tility nd uppre multiple wing oilltion, the optiml time of line reloing hould e et to gurntee minimum of the trnient energy ro the utet m t the intnt. A i utet m B Figure 5: Inter-re power ytem nd it utet The trnient energy ro the utet m n e deried uing Eqution (6) nd ( i PE( i = P( i u P( i ( i [ ( ) ] du (7) Figure 6 how the power-ngle urve for trnferring power etween u i nd with different line re-

4 P ) loing time. ( i i the pre-fult tedy-tte power flow. ( ( i ) nd P ( i ( ( i ) re the powerngle tretorie without nd with ingle line tipped, repetively. P (i- ( (i-) '' P (i-( (i-) o' o ' () line reloing t ' o" o' o ' () line reloing t '' ' = ( i ' = ( i mx min ( i ( i Figure 6: Trnient fult optiml reloure For the e of diuion, trnient fult w umed ourring t tie-line, nd w uequently lered y tripping the fulty line. When thi fult w lered, the ytem operting point withed from the fult-on tretory to the pot-fult tretory P(i (with tie-line tripped) t poition. ) A the ytem reover, the operting point move long tretory P(i from point to where the line ngle differene rehed ) it mximum. The trnient energy ro the utet m t thi point n e repreented y the re. 4.1 Option 1 If the reloure our t thi time, the operting point will with from the pot-fult to pre-fult tretory, i.e. from point to, nd then move to point long tretory P ( i. A reult, the trnient energy ro the utet m eome ) the re o. Thi indite tht the utet m would eome le tle the more trnient energy i ineted into thi utet. In other word, line reloure t the time when the line ngle differene rehing it mximum will deteriorte interre power ytem. 4.2 Option 2 Now, let onider nother e with line reloed t the time when the line ngle differene rehe it minimum inted t the operting point. If the reloure our t thi point, the operting point will with to nd the trnient energy ro the utet m will eome re o o inted of oo, i.e. the ytem tility will e improved the trnient energy i redued. A only the firt minimum line ngle differene point detetion i required in thi line reloing heme, it implementtion i the implet ompred to the one deried elow. 4.3 Option 3 In ddition to option 1 nd 2, there i nother option uggeted in [3] to reloe the line when the line ngle differene i loer to it pre-fult equilirium tte (point o ), i.e. t the operting point d hown in Figure 7, in order to otin etter ytem tility. A the operting point i withed to o, it ontinue to wing to point d nd then return. The trnient energy ro the utet m i redued to re o d d, nd reult improve the ytem tility. P (i-( (i-) d' d" o' o d ' ' ( i Figure 7: Line reloing t the pre-fult lne point 5 CAE TUDIE Two tet ytem were eleted here to illutrte the vlidity of the method propoed. One i one mhine infinite u ytem hown in Figure 2. The other i redued Northet Chin Power ytem hown in Figure One mhine infinite u (OMIB) ytem A trnient fult our t one of two iruit etween u 2 nd u 3. Thi fult i lered y tripping the fulty line out t.15e. With repet to vriou reloing time, the following 4 e re preformed. Ce 1: line tipped without reloing. Ce 2: reloing t.42e when the ngle differene of line 2-3 rehe it mximum. Ce 3: reloing t.86e when the ngle differene of line 2-3 rehe it per-fult equilirium point. Ce 4: reloing t.99e when the ngle differene of line 2-3 rehe it minimum.

5 Figure 8 plot the genertor rotor ngle orreponding to the ove 4 e. A illutrted in thi figure tht the ytem tility eome wore (in Ce 2) if tieline i reloed when the line 2-3 ngle differene reh it firt mximum; the pot-fult oilltion hve een ignifintly redued in Ce 3 nd 4 with Ce 4, where the reloing time w et to the time when the ngle differene of line 2-3 rehe it minimum, eing lightly etter. wing ngle(deg) time() Figure 8: Plot of genertor rotor ngle No reloure reloing t.42 reloing t.86 reloing t.99 The tility enhnement provided in Ce 3 nd 4 n e explined with the plot of the line 2-3 potentil energie nd the genertor ineti energie hown in Figure 9 nd 1. A diued in previou etion, the trnient energy indeed inreed in Ce 2 nd dereed in Ce 3 nd 4 when ompred to the e e without line reloure. It i eue Ce 4 i the mot effetive one in reduing the trnient energy ro the utet m, it n uppre uequent ytem oilltion the mot. potentil energy etween u No reloure time() Figure 9: Plot of line 2-3 potentil energy 4 reloing t.42 reloing t.86 reloing t YINMIN 5K TRANMIION YTEM ytem deription Thi i redued Northet Chin ytem onited of 1 generting unit inluding 3 equivlent ytem hown in Figure 11. Thi ytem i hrterized y the lrge remote genertion plnt, uh YMC, HC1 nd HC2, onneted vi n extremely hevily loded 5 doule-line. The mority of eletri power i upplied from YMC plnt to lod enter A nd from the HNB primry ttion to the HXB ttion to equivlent ytem 1. YMC i hevily loded genertor group. The pe power flow from YMC to FTB nd from HNB to HXB re 184MW nd 1216MW, repetively. YMC FTB DQB BJB QYB QBB HJB FYB FEC FEB A RHL XFB EHB XHC HQB Equvilent ytem 1 HNB HXB HC1 HC2 HXB Equvilent ytem 2 5K trnmiion line 22K trnmiion line Figure 11: Redued Northet Chin ytem imultion reult HRC HDB Equvilent ytem 3 A 3-phe trnient fult w pplied t one of two iruit etween u DQB nd HNB. They re the tieline of the two u-ytem eing onidered. Thi fult w lered t.12 y tripping out the fulty line. Without ny reloure, the ngle differene etween u DQB nd HNB reh it mximum, per-fult equilirium point nd minimum t.75, 1.27 nd 1.57, repetively. Agin 4 e ed on thoe timing were reted, nd the rotor ngle of genertor YMC reltive to u HXB were plotted in Figure 12 for thee 4 e. The reult otined re imilr to thoe in the OMIB ytem tht the pot-fult oilltion were redued in Ce 3 nd 4 with Ce 4 eing lightly etter. Kineti energy time() No reloure reloing t.42 reloing t.86 reloing t.99 Figure 1: Plot of genertor ineti energy 4 wing ngle (DEG.) open t.12, no reloure open t.12, reloing t.75 open t.12, reloing t 1.27 open t.12, reloing t Time() Figure 12: Plot of YMC rotor ngle reltive to HXB u

6 line potentil energie open t.12, no reloure open t.12, reloing t.75 open t.12, reloing t 1.27 open t.12, reloing t Time() Figure 13: Line DQB-HNB potentil energy The line DQB-HNB potentil energie re hown in Figure 13 nd give imilr piture the OMIB ytem gin, i.e. the trnient energy inreed in Ce 2 nd dereed in Ce 3 nd 4 when ompred to the e e without line reloure. A reult, the uequent pot-fult wing oilltion were dmped more if the line i reloed t 1.57, when the voltge ngle differene etween u DQB nd HNB rehed it minimum. On the other hnd, if line reloed t the.75, the ytem tility eme wore. 6 CONCLUION By exmining the propertie of the topologil trnient energy funtion, it n e onluded tht ytem tility nd inter-re oilltion ould e gretly improved if the trnient energy of ritil lol networ i minimized. A reult, new methodology for eletion of reloing time w developed for dmping the interre power ytem oilltion nd enhning trnient tility. The lgorithm propoed i ed on minimizing the utet potentil energy nd h the dvntge tht it i le to pture the optiml reloure time in rel time, i.e. the heme i dptive to the ytem opertion ondition nd fult ondition, nd only limited numer of dt meured t one lotion on tieline lining u-networ re needed, i.e. thi void the need for meuring nd trnmitting lrge numer of dt glolly. 7 ACKNOWLEDGEMENT The uthor grtefully nowledge the upport of the Hong Kong Polytehni Univerity nd the Reerh Grnt Counil of the Hong Kong peil Adminitrtive Region. REFERENCE [1] IEEE Committee Report: ingle phe tripping nd reloing of trnmiion line. IEEE Trn. on Power Delivery, ol.7, No.1, pp , [2] Prh Kundur: Power ytem tility nd Control. MGrw-Hill, In [3] Z.O.Bo, R.K.Aggrwl, A.T.John, et l.: New onept in trnmiion line reloure uing highfrequeny fult trnient. IEE Pro - Genertion. Trnmiion. Ditriution, ol.144, No.4, pp , [4] D..Fitton, R.W.Dunn, R.K.Aggrl, A.T.John, nd Y.H.ong: The pplition of neurl networ tehnique to dptive utoreloure in protetion equipment. Fifth Interntionl Conferene on Development in Power ytem Protetion, pp , [5] Amr G.Bhh, nd Adly A.Girgi: An invetigtion on the effet of line reloing on trnient tility ement for multi-mhine power ytem. Power Engineering oiety ummer Meeting, ol.2, pp , [6] Yuhun Yun, Bohui Zhng, nd Qingfng Wu: A method for pturing optiml reloure time of trnient fult. POWERCON'98, ol.2, pp , [7] Bohui Zhng, nd Yinghui Lin: Mthemtil model for nlyi the effet of reloure intervl time on power ytem. POWERCON'98, ol.2, pp , [8] A.R.Bergen, nd D.J.Hill: A truture preerving model for power ytem tility nlyi. IEEE Trn. on Power Apprtu nd ytem, ol.1, pp.25-35, [9] K..Chndrhehr, nd D.J.Hill: Cutet tility riterion for power ytem uing truturepreerving model. Eletri Power nd Energy ytem, ol.8, No.3, pp , BIOGRAPHIE K.W. Chn reeived hi B(Hon) nd PhD Degree in Eletroni nd Eletril Engineering from the Univerity of Bth (UK) in 1988 nd 1992, repetively. He oined the deprtment of Eletril Engineering of the Hong Kong Polytehni Univerity in 1998 leturer. G. W. Ci reeived hi M. nd PhD form Eletril Engineering from Northet Chin Intitute of Eletril Power Engineering nd Hrin Intitute of Tehnology, P.R.Chin in 1993 nd 1999 repetively. He viited the Hong Kong Polytehni Univerity Reerh Aitnt in 2. T.. Chung otined B. from Hong Kong Univerity, M. from Imperil College London nd Ph.D trthlyde Univerity, U.K. Hi i urrently Profeor nd Power Group Leder in Hong Kong Polytehni Univerity. G. Mu reeived hi Ph.D in Eletril Engineering from Tinghu Univerity, Chin, in He i urrently Profeor of Northet Chin Intitute of Eletril Power Engineering, Chin. Hi reerh interet re in the re of power ytem nlyi.