VOLTAGE SAG COMPENSATION OF POINT OF COMMON COUPLING (PCC) USING FAULT CURRENT LIMITER IN THREE PHASE LINES

VOLTAGE SAG COMPENSATION OF POINT OF COMMON COUPLING (PCC) USING FAULT CURRENT LIMITER IN THREE PHASE LINES P.ANUSHA & K. SWARNASRI Department of Eletral & Eletrons Engneerng, R.V.R &J.C.College of Engneerng, Chowdaaram, Guntur, A.P, Inda. Emal: peram00@gmal.om, : swarnasrk@gmal.om AbstratThs paper presents a new omponent alled Fault Current Lmter () n three phase lnes. Voltage sag ompensaton s proded on both sdes of the Pont of Common Couplng (PCC) by usng FTS Dees (STATCOM, APF, DSTATCOM, DVR, UPFC) and. The FTS dees prode ompensaton on nput sde and prodes ompensaton on output sde. A senste load s onsdered at output sde of PCC. The man objete of the desgned omponent s to protet the senste load from the shunt faults. The ompensaton s beng proded at output sde of PCC. Load oltage redues upon the ourrene of shunt fault. Ths results n unbalane of the system oltages and phase angle jump. The foremost purpose of the would be to lmt the oltage sag and the phase angle hange of the substaton pont of ommon ouplng. IGBT based s desgned n ths paper nstead of Thyrstor based. When IGBT s used as swthng dee, wll hae redued a sde losses and nreased speed of operaton. DC sde reator alue an be redued to a lower alue. Lowered Total Harmon Dstorton (THD) and mproed oltage wae form at PCC shows the effete ness of the desgned. The analyss and desgn s arred out n MATLAB wth SIMULIN K smulaton pakage. Index Terms Fault Current Lmter (),Pont of Common Couplng (PCC), Total Harmon Dstorton (THD), Power Qualty (PQ). I. INTRODUCTION Now a day s power system network beomes ery omplex due to rapd hanges n deelopment. There s a great desre for mprong power qualty beause of growng demand of eletral energy. There are so many power qualty problems.e. malfuntonng of the ontrol systems and oltage sag et. that are affeted on the power transmttable apaty of the transmsson system. The oltage sag problem rses due to nreasng the senste load demand. The oltage sag problems are mostly appears n buses whh are onneted to radal feeders [][6]; results loss of oltage qualty. The dynam oltage restorer (DVR) s most ommonly used for oltage sag ompensaton whh wll njet the ompensated oltage wth magntude and phase angle n seres wth the dstrbuton feeders [7],[8]. Durng the fault the oltage sag s proportonal to the short rut urrent leel. The leels of fault urrent n dfferent plaes hae often exeeded the wthstand apaty of exstng power system equpment due to ths the stablty and relablty of the power system wll be redues[9]. Thus, the fault urrent of the power system s lmtng to a safe leel an greatly redue the rsk of falure to the power system equpment due to hgh fault urrent flowng through the system. The leels of fault urrent are ontrolled by super ondutng fault urrent lmter (S) due to ther arable mpedane haratersts but the ost of super ondutors s hgh. Therefore, the super ondutng ol s replaed wth non superondutng ol n the. The non ondutng ol exhbts power loss whh s neglgble as ompared wth the total power proded by the radal feeders. In ths paper IGBT based s proposed for oltage sag and phase angle jump mtgaton of the substaton PCC. II. VOLTAGE SAG IN POWER SYSTEM Fg. shows the snglelne dagram of the three phase power system. Ths fgure shows a substaton wth sx feeders (F,F,F3,F4,F5,F6). For an easy analyss of the three phase lnes we are onsder only one phase nstead of three phases. BUS BAR TRANSFORMER PCC F Senste load Senste load Senste load Fgure. Snglelne dagram of the three phase power system The below fgure shows the sngle lne dagram of the power system, here we are onsderng only one phase whh s hang two feeders F and F. Feeder F supples a senste load and F s faulted. F F3 F4 F5 F6 Internatonal Conferene on Eletral Eletrons and Computer SeneEECS9th Feb 04ISBN97893869354 06

Voltage SAG ompensaton of pont of ommon ouplng (PCC) usng fault urrent lmter n three phase lnes BUS BAR TRANSFORMER PCC F F Fault Senste load Z Phasorof the load mpedane at the F. In the normal state Z K(N), s larger than ZS Z t. So the PCC oltage s approxmately equal to the soure oltage. In the fault ondton n the F, the oltage and phase angle of substaton PCC an be expressed as follows: Fgure. Snglelne dagram of the power system Fg.3. shows the postesequene equalent rut of the ase study system n the fault ondton. To alulate the oltage sag, the smple oltage dder method s ntrodued n [0]. Zs BUS BAR Z t PCC Z l Z l Fault Z f Z sl Z F F Senste load Fgure3.Postesequene equalent rut of the ase study system n the fault ondton. In the normal operatng ondton, the oltage magntude and ts phase angle n the substaton PCC an be expressed as follows: Z K(N) V PCC(N) = V Z S Z t Z S K(N) () V PCC N = Z K(N) Z S Z t Z K(N) V S () Φ PCC N = ar tan X K(N) R K(N) (3) Where ar tan X K(N)X S X t R K(N) R S R t V PCC(N) Voltage magntude of the PCC n normal state. V PCC(N) Voltage phasor of the PCC n normal state. Φ PCC(N) Phase angle of oltage of the PCC n normal state. Where the phase angle of Vs s onsdered to be zero ZtPhasor of transformer mpedane. ZK(N) = R K(N) jx K(N) Equalent mpedane of parallel feeders n normal state. V S Phasor of soure oltage. ZS = R S jx S Phasor of soure mpedane. Z K(N) =( Z LZ SL ) (Z L Z ) (4) V PCC(F) = V PCC F = Z K(F) Z S Z t Z K(F) V S (5) Z K(F) Z S Z t Z K(F) V S (6) Φ PCC F = tan X K F R K F Where V PCC(F) durng fault Φ PCC(F) durng V PCC(F) fault Z F tan X K F X S X t R K F R S R t (7) Voltage magntude of the PCC Phase angle of oltage of the PCC the fault ZK(F) = R K(F) jx K(F) oltage phasor of the PCC durng Fault mpedane. Equalent mpedane of parallel feeders durng fault s ZK(F) = ZL ZSL Z L ZF (8) In the threephase fault ondton.e.symmetral fault ondton, the fault mpedane (Z F )sapproxmately equal to zero and aordng to equaton (8) the magntude of Z K(F)wll be small. Durng the faultthe oltage sag and phase angle jump of the senste load s omparately worse. To preent oltage sag and phase angle jump durng a fault, a new omponent s ntrodung between the substaton PCC and the fault loaton for prodng large lmtng mpedane. A new omponent s known as. II. CONFIGURATION AND ITS OPERATION The Fault Current Lmter () s defned as t s a arable mpedane dee onneted n seres wth a rut to lmt the urrentunder fault ondtons [4]. Durng normalondton the should hae ery low mpedane and under fault ondton t should hae hgh mpedane [5,6]. has potental to redue fault leel on the eletrty power networks and may ultmately lead to lower rated omponents beng used or to nreased apaty Internatonal Conferene on Eletral Eletrons and Computer SeneEECS9th Feb 04ISBN97893869354 07

Voltage SAG ompensaton of pont of ommon ouplng (PCC) usng fault urrent lmter n three phase lnes onexstng systems[4]. lmts the short ruturrent to an aeptable leel[7,8]. Fg.4 shows Fault Current Lmter () rut topology whh s formed by omposng of two nddual parts. ) Brdge part that nludes a dode retfer brdge, a small d lmtng reator (L d ).resstane (R d ), a semondutor swth (IGBT or GTO),and a freewheelng dode(d 5 ). ) Shunt branh as a ompensator that nludes a resstor and an ndutor (R sh jωl sh ). V SWF Forward oltage drop on the semondutor swth I ae Aerage of dodes urrent n eah yle that s equalto I peak /π Consderng (9) the power loss beomes a ery small perentage of the feeder s transmtted power. In the fault ondton, the PCC oltage drops on the shunt mpedane. Therefore, the lne urrent wll bypass through the shunt resstor (R sh ). As a result, power loss on the R sh depends on ts alue. Note that the fault ondton s more than a few yles and t s a small tme nteral. III. CONTROL STRATEGY Fgure 4. Fault Current Lmter () rut topology. Preously thyrstor based s used nstead of one semondutor dee (IGBT) at brdge arms for redung the leels of the fault urrent.thyrster based posses two lmtatons frst, they hae more omplated ontrol system. Seond, onsderable oltage drop on the and the a power loss on the shunt branh mpedane, d reator power loss n the normal operatng ondton. In the proposed topology IGBT based s used to redue the oltage drop and power losses, nrease the speed of operaton. It s possble to hoose a small alue for L d to preent seere rate of hange of urrent at the begnnng of the fault ourrene. In the normal operatng ondton the has the power losses on the retfer brdge dodes, IGBT, R d.therefore,the power loss of ths an be alulated as P loss = P R P D P SW where Id V DF = R d I d 4V DF I ae V SWF I d (9) d sde urrent whh s equal to the peak of lne urrent Forward oltage drops on eah dode Fg.5 shows the ontrol rut of the. In the normal operatng ondton of the power system, IGBT s turned ON and the lne urrent ( L ) flows through D, L d, IGBT, D4 and D3, L d, IGBT, D n poste and negate alternates, respetely. So, L d s harged to the peak of the lne urrent and behaes as a short rut. Usng semondutor dees and a small d reator ause a neglgble oltage drop on the. Durng fault ondton, I d beome greater than the maxmum permssble urrent I m. The ontrol rut detets t and turns the semondutor swth off. So the brdge retreats from the feeder, and the shunt mpedane enters the faulted lne and lmts the fault urrent. At ths moment, the freewheelng dode dsharges L d. In fat, the freewheelng dode s used to prode a free route for the d reator urrent when the semondutor swth s OFF. Fgure 5. Control rut of the proposed After the fault s remoed, whle the semondutor swth s OFF, shunt mpedane wll be onneted n seres wth the load mpedane. Therefore, lne urrent wll be redued nstantaneously. To detet ths nstantaneous reduton of lne urrent, L s ompared fault urrent (I f ) wth that an be alulated from I f = V PCC R sh jω L sh (0) Internatonal Conferene on Eletral Eletrons and Computer SeneEECS9th Feb 04ISBN97893869354 08

Voltage SAG ompensaton of pont of ommon ouplng (PCC) usng fault urrent lmter n three phase lnes When the dfferene of lne urrent ( L ) and fault urrent(i f )beomelarger than as the fault remoal sgn, the ontrol rut turns the semondutor swth ON. So, the power system proeeds to the normal state. The alue of k an be alulated from as k = V PCC Z sh V PCC () Z sh Z L,mn (3.) wherez sh s the shunt mpedane, and Z L,mn s the mnmum mpedane of load on the proteted feeder. By the use of dodes,igbts and small d reator there s a oltage drop on.ths results harmon dstorton on load oltage and power loss n shunt branh n normal operatng ondtons.the oltage drop on power eletron dees s ompensated by onsderng a d soure n the proposed. So t redues the total harmon dstorton (THD) of oltage waeform. Benefts of the : s offer numerous benefts to eletr utltes. For nstane, utltes spend mllons of dollars eah year to mantan and protet the grd from potentally destrute fault urrents. These large urrents an damage or degrade rut breakers and other expense T&D system omponents. Utltes an redue or elmnate these replaement osts by nstallng s. Other benefts nlude:. Enhaned system safety, stablty, and effeny of the power delery systems.. Redued or elmnated wdearea blakouts, redued loalzed dsruptons, and nreased reoery tme when dsruptons do our. 3. Redued mantenane osts by protetng expense downstream T&D system equpment from onstant eletral surges that degrade equpment and requre ostly replaement. 4. Improed system relablty when renewable and DG are added to the eletr grd. 5. Elmnaton of splt buses and openng buste breakers. 6. Redued oltage dps aused by hgh resste system omponents. 7. Sngle to multple shot (fault) proteton plus automat resettng III. DESIGN CONSIDERATIONS For desgnng shunt branh parameters, t s possble to onsder the followng ondtons.. In the deal ase, shunt branh mpedane s equal to load mpedane.. When a fault ours n the proteted feeder, the oltage sag at the PCC wll be zero. Howeer, t s dffult to equate these mpedanes exatly beause of the load araton on dstrbuton feeders. So t s dffult to estmate the sutable alue for L sh and R sh. From a pratal pont of ew, parameters of the shunt branh an be resolute by usng the hstory of load measurements at the proteted dstrbuted feeder. It s obously the power and urrent flowng through the feeders s hange. For the alulaton of L sh and R sh alues, aerage mpedane of the proteted feeder s alulated. So L sh and R sh are hosen to be equal to ts ndutane and resstane. The horzontal axs of ths Fg.6(a) shows the magntude of load mpedane n per unt where the base alue s ts mpedane of the deal ase. The dashed lne represents the exstene of the deal ase. The rato of reatane to resstane of shunt branh s kept onstant n ths fgure. The parameter of ths fgure s the magntude of soure mpedane. Ths fgure shows that for a large range of load magntude aratons (0.5 to p.u. wth a fxed shunt branh mpedane), the oltage magntude of PCC for the post fault ondton hanges n an aeptable range espeally for low alues of ZS. Fg.6(b) shows the phaseangle deaton of the PCC from ts base alue that s the phaseangle deaton of pre fault PCC oltage. The horzontal axs of ths fgure s the rato of reatane to resstane of shunt branh n per unt where the base alue s obtaned from the deal ondton. Ths fgure shows that t s possble to derease the resstane of the shunt branh (wthout hangng the magntude of tsmpedane) n a large range wthout any onsderable phaseangle jump durng fault. Dereasng R sh redues the power loss of the shunt branh durng the shortrut nteral. So ts desgn beomes smpler. Fgure 6(a) Magntude of the PCC oltage. Internatonal Conferene on Eletral Eletrons and Computer SeneEECS9th Feb 04ISBN97893869354 09

r Voltage Soure r Voltage Soure r Voltage Soure tf tf tf3 l l6 l l0 l5 l9 3 5 8 I Goto I Goto3 I3 Goto5 l3 l7 3 l V Goto Measurements V Goto4 4 V3 Goto6 7 Generator Generator Generator Breaker Dsrete, Ts = 5e005 s Breaker powergu 6 Breaker l4 l8 l r Voltage Soure r Voltage Soure r Voltage Soure tf tf tf3 l l6 l l0 l5 l9 3 e e 5 8 I Goto e e I Goto3 e e I3 Goto5 l3 l7 3 l V Goto Measurements V Goto4 4 V3 Goto6 7 Generator Generator Generator Breaker Dsrete, Ts = 5e005 s Breaker powergu 6 Breaker l4 l8 l Voltage SAG ompensaton of pont of ommon ouplng (PCC) usng fault urrent lmter n three phase lnes Fgure 6(b) Phase angle deaton of the PCC. IV. SIMULINK MODELING AND RESULTS OF Ths topology has been mplemented on three phase system and the results are presented n ths seton. Three phase system s onsdered for the analyss and smulaton beause t would be more pratal to arry out the analyss on the wdely used three phase senste loads n ndustres. Durng the three phase balaned fault ondton, wthout usng the, the oltage sag appears seerely at PCC.when s used t wll redues the fault urrent as well as the oltages of the other feeders are restores to the normal alue. The mproes the system relablty and oltage qualty. The system parameters are n Table I. The smulatons are obtaned usng the MATLAB/SIMULINK software. Fgure7. Smulaton model of three phase system wthout Three sngle phase soures are taken for smulaton and the ombned oltage wae form at PCC durng the three phase fault reated at t=0. se to t=0. se s plotted n Fg.8, Fg.9 shows the nstantaneous power n frst phase of the system at PCC wth fault ondton. Fgure 8.Three phase oltages at PCC wthout. Table I: System parameters Soure Power soure 0k,50Hz,X/R rato:5 Total Impedane:.608Ω Sde Data Transform er 0k/6.6k,0MVA,0. pu Dstrbut Feeder F j0.34ω on Feeders Data Feeder F J0.57Ω L d =0.0H,R d =0.03Ω V DC Sde DF =3V,V SWF =3V,Im=0. 6kA Data Swth type: IGBT Shunt Branh L sh =0.08H,R sh =5Ω Load Data Senste load 0j5.7Ω Load Of F 5j3.3Ω Fgure9.Power Waeform at PCC for one phase Fg. 0.Sshows smulaton model of three phase system wth.when the fault s ours the nserts large mpedane n to the faulted lne and preents the oltage sag and phase angle jump at the substaton PCC. Fgure0. Smulaton model of three phase system wth Internatonal Conferene on Eletral Eletrons and Computer SeneEECS9th Feb 04ISBN97893869354 0

Voltage SAG ompensaton of pont of ommon ouplng (PCC) usng fault urrent lmter n three phase lnes V. CONCLUSION Fgure.Three phase oltages at PCC wth. Fgure.Voltage drop aross. In ths paper, oltage sag ompensaton, phaseangle jump mtgaton, and fault urrent lmtng operaton were analyzed. The desgned s apable of mtgatng oltage sag and phaseangle jump to aeptable leels. By usng the semondutor swth n the d urrent path nstead of two numbers of Thyrstors at the brdge branhes, the wll hae hgh speed and onsequently, the d reator alue s redued to a lower alue.in addton, the d oltage soure plaed n the struture redues ts THD and a losses n normal operaton. In general, ths type of, wth the smple ontrol rut and low ost, s useful for the oltagequalty mproement beause of oltage sag and phaseangle jump mtgatng and low harmon dstorton n dstrbuton systems. In addton to that three phase power systems are deeloped wth and wthout the as well as ther behaors are also obsered. REFERENCES [] J. V. Mlanoand y. Zhang, Modelng of Fats dees for oltage sag mtgaton studes n large power systems, IEEE Trans. Power del., ol. 5, no. 4, pp. 3044 305, ot. 00. [] T. J. Browne and G. T. Heydt, Power qualty as an eduatonal opportunty, IEEE Trans. Power Del., ol. 3, no., pp. 84 85, May008. [3] N. Ertugrul, A. M. Gargoom, and W. L. Soong, Automat lassfatonand haraterzaton of power qualty eents, IEEE Trans. PowerDel., ol. 3, no. 4, pp. 47 45, Ot. 008. Fgure 3.Shunt Current. [4] M. Abapour, S. H. Hossen, and M. T. Hagh, Power qualty mproementby use of a new topology of fault urrent lmter, n Pro. ECTICON,007, pp. 305 308. [5] M. Brenna, R. Faranda, and E. Tron, A new proposal for powerqualty and ustom power mproement: Open UPQC, IEEE Trans.Power Del., ol. 4, no. 4, pp. 07 6, Ot. 009. [6] W. M. Fe, Y. Zhang, and Z. Lü, Noel brdgetype based on selfturnoffdees for threephase power systems, IEEE Trans. PowerDel., ol. 3, no. 4, pp. 068 078, Ot. 008. Fgure 4.DC Sde Current. [7] E. Babae, M. F. Kangarlu, and M. Sabah, Mtgaton of oltage dsturbanesusng dynam oltage restorer based on dret onerters, IEEE Trans. Power Del., ol. 5, no. 4, pp. 676 683, Ot. 00. [8] M. Moradlou and H. R. Karshenas, Desgn strategy for optmum ratngseletonof nterlne DVR, IEEE Trans. Power Del., ol. 6, no.,pp. 4 49, Jan. 0. [9] Fabo, Tosto; Voltage Sag mtgaton on Dstrbuton Utltes, ETEP European Transaton on Eletr power, Vol. (), pp. 7, January/February 00.. [0] L. E. Conrad, Proposed hapter 9 for predtng oltage sags (dps) nreson to IEEE std. 493, the gold book, IEEE Trans. Ind. Appl., ol.30, no. 3, pp. 805 8, May/Jun. 994. *** Fgure 5.Three phase power. Internatonal Conferene on Eletral Eletrons and Computer SeneEECS9th Feb 04ISBN97893869354