Pro. of the 5th WSEAS/IASME Int. Conf. on Eletri Power Systems, High Voltges, Eletri Mhines, Tenerife, Spin, Deemer 16-18, 2005 (pp496-502) Lrge Sle Wind Power Integrtion into Power Networks Using SVS nd Series Retne Mnuel A. Aost P. Prof. Roerto Alves B. Trnsmission Plnning Dpt. Energy Conversion nd Trnsport Dpt. CVG EDELCA Simón Bolívr University Crs, Venezuel Crs, Venezuel www.edel.om.ve www.us.edu.ve Astrt: - The use of utomti retive power ompenstion nd series retnes s n dpttion mehnism for lrge sle wind power integrtion into power networks is disussed in this pper. The uthors investigted the enefits of this mehnism iming to void the usul lrge wind genertion disonnetions when voltge dip ours in power system due to fults in lines or other devies. The uthors evluted the impt in the ritil lering fult time in power system due to the insertion of the retive ompenstion nd series retnes in the wind prk s mesure of the enefits hieved with the dpttion mehnism. The results demonstrted the onveniene of this king of mehnism tht n e used with onventionl indution genertors or douly-fed indution genertors. Even when the evlution ws mde using the Venezueln grip opertion uthority riteri, sensiility evlution ws mde using the low voltge ride through pility urve riteri, nd the results in oth ses onfirmed tht this mehnism ould e hep solution in onventionl wind prk nd for new ones s well, to void the wind genertors disonnetion when voltge dip ours in the power network. Key-Words: Retive Power Compenstion, Lrge Wind Power Genertion, Critil Clering Fult Time, Series Retne, Low Voltge Ride Through Cpility Curve. 1 Introdution Conventionl squirrel ge indution genertors nd new tehnology genertors, like rotor power onverter ontrolled genertors (douly-fed indution genertor), re expose to huge rotor urrent during lrge voltge dip used y fults in the power networks. During the dip nd some seonds fter the fult is ler in the network, the onventionl genertors drin too muh urrent in the rotor s onsequene of the slip inrement droved y eletri nd mehnil energy unlne. Similr effet is present in the doulyfed genertor euse, to void the over dimension in the eletroni iruitry of the onverters, those power ontrollers re y-pssed during the trnsient, onverting those genertors simple onventionl wound rotor indution genertors (with the sme performne thn the squirrel ge ones). During the trnsients, when the power system is trying to use ll the retive power reserve in the network for voltge support nd fst reovery, the genertor s indutive ehvior re entuted onsuming retive power from the network, mking the restortion some times impossile nd onduting the system to voltge ollpse. Network opertors usully prefer the disonnetions of tht kind of genertors nd their reonnetion fter the voltge hs een reovered to norml vlues. This poliy imposed in some regultions implies the use of low voltge rely tht send the disonnetion signl to the min rekers in the ommon oupling point, etween wind prks nd power networks, when pre-set voltge dip vlue is rehed. The disonnetion it self does not men prolem if the tive power reserve re disply ording to this requirements, ut hve to e plnned, dispth nd pid mking the opertion more expensive. Nowdys, the wind power penetrtion nd the reltive importne of this genertion during low demnd dily period, mke the disonnetion somewht impossile, unless n expensive reserve should e hrged to servie users. For this reson, this kind of investigtion is very importnt euse the gol is to find s muh s possile tehnologi solutions to mke the wind power relile soure with the minimum onstrins. Under this ide, this pper shows the results otined using series retne nd stti voltge ompenstor s wind power prk devies. The voltge ompenstor is used for wind genertors voltge support, during nd immeditely fter the fult, nd the series retne hs the purpose to seprte the power network nd the eletri wind power instlltions to redue the onsequenes of network fults into the wind prk nd lso, to redue
Pro. of the 5th WSEAS/IASME Int. Conf. on Eletri Power Systems, High Voltges, Eletri Mhines, Tenerife, Spin, Deemer 16-18, 2005 (pp496-502) the retive requirements from the stti voltge ompenstor. 2 Min Design Considertions 2.1 Indution Genertor used in Wind Power Applitions The most ommon indution genertors used for wind purposes re the squirrel ge indution genertor (SCIG) nd the wound rotor indution genertor (WRIG). The first kind, SCIG, n e onneted diretly through the step up trnsformer to the medium voltge wind prk instlltions, or using nd eletroni interfe. This interfe hs the dvntge tht n ontrolled the eletri nd mehnil intertion etween network nd genertor ut, for lrge wind purposes this interfe hs to e sizing with the min genertor pity mking it expensive nd eonomilly prohiited. The diret onnetion is the most ommon, hep nd widely used type of SCIG in the world. The SCIG, like ny indution mhine, hs strongly voltge nd slip performne dependeny (Fig. 1). Network or Inverter Net Fig 1. SCIG Power Inverter Sttor The WRIG is nowdys spred nd ommonly used in new instlltion with rotor power ontrolled devie onneted to the sme wind prk eletri instlltion. The most ommon rotor ontrollers re the Lod Vrile Control (RLVC) nd the Pulse Width Modultion Inverter (PWMI). The most used is the PWMI ommonly refer s douly-fed indution genertor. Sttor is diretly onneted to the step up trnsformer nd the rotor is lso onneted to the sme inoming eletri instlltion using nother trnsformer for pproprite voltge rnge in the ontroller. Genertor torque nd slip is ontrolled with the rotor eletroni interfe nd, one of the most importnt dvntges, it is possile to ontrol the retive onsumption mking possile no retive power interhnge with the network (Fig. 2). Net Lod or PC PC= Power Converter NET R Net Power Fig 2. WRIG Power Inverter (PWMI) Lod Vrile Controller 2.2 The Power Unlne during Fult Conditions nd the Restortion Proess When the power system t norml ondition, the mehnil power in fed y prime mover equls (power onversion losses negleted) the eletri power generted in ll genertors. In indution genertors the most ritil vrile, the slip, is t nominl vlue (i.e. -0,4 p.u. for typil 2MW wind genertor). A suddenly fult ours in the power system nd the power lne is not mintin ny longer in ny genertors. In the wind genertors, the results will e n importnt slip inrement nd when the fult is ler, those genertors, like ny others, most reover its norml opertion in suh wy tht power interhnge tke ple during some seonds efore new ondition is hieved. During nd fter the fult is lered, ll genertors move one ginst other, nd the wind genertors re not n exeption. The slip inrement in wind genertor oost the indutive ehvior of this mhines, nd rotor nd sttor urrents re so high tht therml dely disonnetion ours s protetion strtegy. In WRIG genertors, efore the disonnetions, ontroller y-pss ours to redue the therml stress over suh devies, voiding n uneonomil ontroller over sizing design. During the y-pss this genertors eomes like SCIG euse rotor re short-iruited. So, during the fult nd some seonds fter it hs een lered, oth kinds of wind genertors ehve most likely from the power intertions nd physil phenomenon point of view. During the fult nd some seonds fter the fult is lered the indution genertors re ting like n indutive lod, onsuming lrge mount of retive power form the system. During this time, restortion proess tke ple in the system where the retive power is needed for voltge reovery
Pro. of the 5th WSEAS/IASME Int. Conf. on Eletri Power Systems, High Voltges, Eletri Mhines, Tenerife, Spin, Deemer 16-18, 2005 (pp496-502) support. But, with the indutive onsumption from the wind prk, the restortion ould e, some times, impossile due to voltge ollpse. This period of time is ommonly studied using the swing motion equtions tht involve ll genertors. In the se of wind genertor those equtions ould e written s: (1) dwt 2 = T K *θ D (w w ) H t dt t s tg dwg 2H = T Te g g (2) dt Eqution (1) is for turine nd genertor intertion nd eqution (2) is for system nd genertor intertion. Even when it ould e possile tht the genertor ould withstnd the high urrents, most opertors prefer the disonnetion of the wind genertor euse it ould e possile to etter support the voltge reovery proess. Tht ws ommon prtie in the pst ut not ny longer sine the reltive weight of wind genertion during the se or low dily lod profile, mke this genertion very importnt in the genertion shre units ommitment. In these ses, when the disonnetion ours during these lod profile onditions, the system must hve enough spin genertion reserved onneted to support the power imlne or to hve nd dequte interonnetion with other systems, to support the imlne through n inrese in the trnsmission interflow. In oth ses the resonly pried unit dispth nd selling/uying ontrts moved something wy form the optiml point, nd tht represent more ost for users. To void this, whole regultion rules hve een hnging to ommnd the permissile onditions in with this kind of genertor n e disonneted. In this wy, the tehnology investigtions re im to find heper solutions to improve the wind genertors performne during fults in the power network. For this purpose, this investigtion ws rried on using the stti voltge ompenstion nd series retne to rete n dpttion mehnism tht improve the voltge response of wind prk during fult onditions in power networks. 2.3 Bsi Design Considertions To develop the study n imginry wind genertion ws reted in whih design ws onsidered rel network loted in some ple of Venezuel (Isl de Mrgrit) where the wind ssessment indites resonle fesiility for one wind prk with 90 MW of pity. So, the design inluded wind prk prototype with 45 units (VESTAS V-80) with 2 s t g MW of pity eh one. An rry of 5 x 9 units were onsidered where eh 5 units where onneted to the sme iruit s indited in figure 3. SVC Ct 1 Ct 2 Ct 3 Ct 4 Ct 5 Ct 6 Ct 7 Ct 8 Ct 9 Fig. 3. Wind Prk Arry The olletor susttion ws onsidered with 3 min usrs with longitudinl rekers nd 1 usr with the stti voltge ompenstor (SVC). The primry voltge of the olletor system is 13,8 kv nd the genertor voltge is 690 V. SCIG genertor ws onsidered nd eh unit ws pitor ompensted in the primry side for 100% power ftor orretion in only one step. The genertor ompenstion ws design under the no lod riteri, so the pitor re onneted in only one step when the genertor is onneted to the min iruit s soon s the wind lows over 4,5 m/s. Under this ondition, ll usses must remin under 1.05 p.u. voltge with minimum genertion in ll units. To fulfill this requirement the sv must hve n indutive rnge to ompenste the high pitive lod under low genertion onditions. The ommon oupling point etween wind prk olletor system nd power network is done through 115 kv usr whih is onneted the olletor system with 2 utotrnsformers 115/. Figure 4 shows the detil of this rrngement. 115/ 90 / 120 MVA OA / OFA 11 % In: 4.600 A XL:? 115 kv SVC 115/ 90 / 120 MVA OA / OFA 11 % In: 4.600 A XL:? Ct 1 Ct 2 Ct 3 Ct 4 Ct 5 Ct 6 Ct 7 Ct 8 Ct 9 33 MVA 33 MVA 33 MVA Fig 4. Susttion rrngement
Pro. of the 5th WSEAS/IASME Int. Conf. on Eletri Power Systems, High Voltges, Eletri Mhines, Tenerife, Spin, Deemer 16-18, 2005 (pp496-502) In figure 4 it n e pointed out the presene of one sv nd two series retnes with therml pity similr to the power trnsformers ut unknown impedne euse tht vlue must e design with the sv to optimize the rnges. The series indutne hs the purpose to eletrilly move wy the network nd the olletor system, in order to minimize the network fult onsequenes over the wind genertors nd to redue the sv requirements. 2.4 SVS nd Series Retne orreltion Figure 5 shows the design model used to ompute the power retive nd series indutne lultion. V nd Vg ws mintined fix t 1.0 pu.u nd the Vs ws hnge to simulte voltge dip from 1.0 pu. To 0.5 p.u. in steps of 5%. The lultions were mde using the PSS/E power flow progrm. Q SVS (MVAr) 450 400 350 300 250 200 150 100 50 0 450 400 350 V=20% V=30% V=40% V=50% 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 Series Retne (p.u.) Fig. 6. SVC nd series retne reltionship for 1MW 300 Q SVS (MVAr) 250 200 V=50% V=40% Network V V g 5*Pg 150 100 V=30% V=20% Min= 153 MVAr jxtd jxl R + jx Rtr+j Xtr 50 xl= 0,375 p.u. V s SVS Q 8*Q C o 5*Q g 0 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 Series Retne (p.u.) Fig 5. Design Model The genertor ws simulted in the middle of the primry olletor iruit to represent the men ehvior of ll 5 genertors onneted long eh primry iruit. Other 40 genertors were simulted s one genertor with the dequte power genertion. Only one power trnsformer nd one series retne ws onsidered euse the design ssumed n-1 riteri for the min susttion. Figure 6 nd 7 shows the reltionship etween the sv retive genertion nd the indutne for different voltge dip. In figure 6 1 MW of genertion in eh unit ws onsidered nd in figure 7 2 MW ws onsidered. 40*P g Fig. 7. SVC nd series retne reltionship for 2 MW The results show tht for mximum genertion of 90 MW in the wind prk, the mximum retive power requirement is hieve. And the mximum, of ourse, is required for the mximum voltge dip. It n e seen tht the series retne redue the retive power requirements in the SVC. A minimum of 153 MVAr is required for the sv nd orrespond to 0,375 p.u. of series retne. An optimiztion proess ws onsidered inluding investment onsidertion. A new urve ws developed in fig 8 were the eonomi optiml vlue for the sv is 160 MVAr nd series retne of 0,3 p.u.
0 Pro. of the 5th WSEAS/IASME Int. Conf. on Eletri Power Systems, High Voltges, Eletri Mhines, Tenerife, Spin, Deemer 16-18, 2005 (pp496-502) 18 l/3 16 Xl Ztr/5 14 Compenstion Cost(SVS + Xl) Million of US$ 12 10 8 6 4 Q svs = 160 MVAr SVC Xl l/3 Ztr/5 l/3 2 115 kv Ztr/5 0,69 kv 0 0,05 0,1 0,15 0,2 0,25 0,3 0,35 0,4 0,45 Series Retne (p.u.) Fig. 8. Eonomi Optimiztion The SVC ws lso required to hve n indutive rnge to mintin 5% mximum voltge rnge over the nominl vlues. 3 Power System Simultions 3.1 Power Flow Results The simultion were done representing the network shown in figure 9, were there re two min power soures esides the wind prk: therml power plnt with 220 MW of instlled pity nd le interonnetion with min lnd (115 kv). 115 kv To Chopt Plt. Luis Cáeres Fig. 9.The power system of Mrgrit Islnd The wind prk model used in power flow progrm is show in figure 10, were eh mhine group represent 5 genertion units. Fig. 10. The wind prk representtion The simultions were done for three wind genertion onditions relted to its pity: 100%, 70%, 40% nd 3%. The system response ws very suessful nd no voltge violtions were fund t ny uses for ny single ontingeny pplied. The 40 MVAr of indutive rnge in the SVC ws orretly dimensioned nd ws heked under the low genertion ondition simulted. Also, no myor retive power is interhnged etween the network nd the olletor system ws found. 3.2 Dynmi Results: Critil Clering Fult Time For dynmi simultions flux linkge model for indution genertor ws used to represent the wind genertors. The turines nd genertors were simulted s one mss nd no mehnil power ws onsidered onstnt during the run time. The min mhines hrteristis use in the simultion were: H= 5 s T = 0,1 s T = 1,53 s X= 4 p.u. X = 0,3 p.u. X = 0,2 p.u. Xl= 0,1 p.u. The simultions were done using the sme softwre used for lod flow nlysis. The therml units in the network were represented in detil using the urrent dt of genertors, governors nd exittions models. The minlnd system ws onsidered s n infinite us. The gol in these simultions ws to evlute the ritil lering time (CCT) for ny fult in the network ompring the wind prk with nd without the ompenstion mehnism. Figure 11 shows the result of ritil lering time without the ompenstion mehnism.
10,0 Pro. of the 5th WSEAS/IASME Int. Conf. on Eletri Power Systems, High Voltges, Eletri Mhines, Tenerife, Spin, Deemer 16-18, 2005 (pp496-502) Cyles 30,0 28,0 26,0 24,0 22,0 20,0 18,0 16,0 14,0 12,0 Los Millnes L Asunión Porlmr El Tirno Luis Cáeres 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% % Wind Genertion Fig. 11. CCT without ompenstion mehnism The worst wind genertion ondition to define the ritil lering time is 100%. This restrition is first loted in Luis Cáeres nd El Tirno susttions. This result is expetle euse for this ondition of wind genertion, oth susttions represents the voltge support nodes in this power systems, so it is expetle tht fults in these susttions re more restritive thn in others. The sttement is verified when wind genertions omes less import in proportion to the therml nd min lnd power soure. When no wind genertion is presented, Luis Cáeres is more representtive for lering time purposes. Figure 12 shows the sme evlutions ut onsidering the dpttion mehnism. Cyles 30,0 28,0 26,0 24,0 22,0 20,0 18,0 16,0 14,0 12,0 10,0 Porlmr Luis Cáeres El Tirno 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% % of Wind Genertion Los Millnes L Asunión Fig. 12. CCT with ompenstion mehnism As n e seen, the ritil lering times in ll susttions hve inresed onsiderly. Here, like in the previous ses nlyzed, the Luis Cáeres susttion represents the most ritil se nd it is presented for 100% of wind genertion. El Tirno susttion shows similr ondition in this se, it hs the sme ritil lering time like in Luis Cáeres. The reson is due to in this se, oth susttion represents the most importnt nodes from the voltge regultion point of view. Unlike the previous se, the presene of n SVS gives more importne to this susttion for voltge support purposes. For the Luis Cáeres susttion, the ritil lering time is 18% igger with the ompenstion thn in the se where no ompenstion ws onsidered. Similrly, for the El Tirno susttions the differene (for 100% of wind genertion) is round 13%. The est mesure of the gin hieved with the ompenstion is represented in figure 13, where oth ses re shown for the min voltge support susttions: Luis Cáeres nd El Tirno. Cyles 35,0 30,0 25,0 20,0 15,0 10,0 WC WNC WNC: Without Compenstion WNC Luis Cáeres El Tirno WC = 18 % 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% % of Power Genertion WC: With Compenstion Fig. 13. CCT omprison It ould e notie tht the mximum enefit hieved y the ompenstion is presented round 75% of the wind power genertion level. But the minimum lering times re for the 100% of the wind genertion. It is very importnt to point out tht those results re sed on the dynmi power system performne riteri used y the Venezueln opertor. In few ses, the ritil times were defined y lost of synhronism in the indution genertor, nd in most ses the trnsient voltges performne were the restritions tht defined the ritil lering fult time. 3.3 Dynmi Results: Low Voltge Ride Through Cpility Curve As sensitivity investigtion, oth ses were nlyzed using the low voltge ride through pility urve (LVRTCC) riteri used in some Europen opertors. Figures 14 nd 15 show some results from the nlysis.
Pro. of the 5th WSEAS/IASME Int. Conf. on Eletri Power Systems, High Voltges, Eletri Mhines, Tenerife, Spin, Deemer 16-18, 2005 (pp496-502) LVRTCC 115 kv Busr Voltges Fult: Luis Cáeres. Tripped line: Luis Cáeres Porlmr Clering Time= 225 ms ( 13,5 Cyles) With Compenstion Se. Fig. 14. CCT using LVRTCC In figure 14 the ritil lering fult time is the sme for the se using the Venezueln opertor riteri. As n e seen, the LVRTCC would give more time for the lering proess euse voltges re over the urve nd no long term lost of synhronism ( typil ehvior present in indution genertor) is present. 115 kv Busr Voltges LVRTCC Fult: Luis Cáeres. Tripped line: Luis Cáeres Porlmr Clering Time= 200 ms ( 12 Cyles) Without Compenstion Se. Fig. 15. CCT using LVRTCC In this se, without ompenstion, the ritil lering fult time is redued euse it n e seen tht the long term lost of synhronism phenomen is present. 4 Conlusion The lod flow nd dynmi nlysis shown tht the ompenstion mehnism using n SVS nd series retne is tehnologil solution tht n e use to minimize the prolems presented in the lrge sle wind power integrtion to power networks. In lrge sle wind power integrtion ses, the ritil lering times nd my e some other prmeters most e evluted for mny wind power genertion level, euse the system do not shown the sme ehvior over the whole rnge of genertion. Voltges in p.u. Voltges in p.u. The mehnism proposed in this pper ould e used in new or in existing wind power instlltions where regultions prohiited the disonnetions of indution genertors when voltge dip ours in the power network. More detiled nlysis must e done for ny prtil se nd n e found tht the ompenstion mehnism gives some dvntges for the whole network nd in suh se, some eonomil ompenstion ould e otined from the mrket tthle to the wind prk profits. Better performne nd hep ompenstion shemes ould e otined in se where the wind genertors ompenstion pitors n e divided in swithle steps. Also, the mehnism ould e improved when the wind prk uses douly-fed indution genertors. Referenes: 1. Le Thu H, Tpn Kumr Sh. Investigtion of Power Loss nd Voltje Stility Limits for Lrge wind frm onnetions to sutrnsmission network. Pper 0-7803-8465-2/04. IEEE 2004. 2. Mgni Plssonm, Trond Toftevgg, Kjetil Uhlen, Jhon Olv Giever Tndle. Lrge-sle Wind Power Integrtion nd voltge Stility Limits in Regionl Network. SINTEF Energy Reserh, Trondheim, Norwy. 3. Ch. Eping, J. Stenzel, M. Pöller, H. Müller. Impt of Lrge Sle Wind Power System Stility.www.kuleuven..e. 4. J.Soens, J. Driesen, D. Vn Hertem, R. Belmns. Generi Aggregted Wind Frm Model for Power System Simultions. ESAT/ELECTRA, K.U. Leuven, Belgium. 5. Koessler, Rodolfo; Pillutl Srinivs; Trinh Ln. Integrtion of Lrge Wind Frms into Utility Grids ABB,In. 2004. 6. P. de Mello, F; Hnnet L.N. Lrge Sle Indution Genertors for Power Systems. Power Tehnology In. Shenetdy, N.Y. IEEE 1980. 7. Ross, Pedro. Dynmi Influenes of Wind Power on the Power System. Thesis of Dotor of Philosophy sumitted to Orsted Institute. Denmrk.2003. 8. Rodríguez Amenedo,J; Alves,R; Arnltes S.; Ríos S. Improving Voltge Stility in Wind Frm y Using SVC. Universidd Crlos III de Mdrid. 2004. 9. Akhmtov Vldislv. Voltge Stility of Lrge Power Networks with Lrge Amount of Wind Power. Interntionl Workshop on Lrge Sle Integrtion of Wind Power nd Trnsmission Networks for Offshore Wind Frms. 2003.