Simulation of a zero-sequence relay for a distribution network with EMTP-RV Discrimination between fault current and magnetizing inrush current

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1 imultion of zero-sequene rely for distriution network with MTP-RV Disrimintion etween fult urrent nd mgnetizing inrush urrent M. Petit, P. Bstrd Astrt-- The zero-sequene relys re widely used to protet rdil feeders of distriution network ginst grounded fults. When fult is deteted relosing sequene is often used to suppress the fult. If these feeders re onneted to MV / LV trnsformers, the losing rely genertes mgnetizing inrush urrent. Then the urrent trnsformers sturtion indues n pprent zero-sequene urrent tht n e seen s fult urrent y the rely. To prevent the rely opening the Hz positive sequene n e used. The dely etween the Hz positive-sequene nd the Hz zero-sequene n help to disriminte fult urrent from mgnetizing inrush urrent. In this pper omplete simultion of suh rely with MTP-RV is desried using oth the power nd ontrol loks ville in the MTP-RV lirry. Keywords: zero-sequene rely, distriution network, fult urrent, inrush urrent. T I. INTRODUCTION H energizing of power trnsformer n generte high trnsient inrush urrents due to ore sturtion. This phenomenon depends on severl prmeters suh s the ore residul mgnetiztion nd the swithing instnt. Moreover the inrush urrents re often poorly mesured due to the sturtion of the urrent trnsformers (CT). A rief nlysis of the mgnetizing inrush phenomenon is reviewed in []. The trnsformers inrush urrents re n importnt prolem for the reliility of the protetion relys: - differentil rely for power trnsformer protetion euse inrush urrents indue flse differentil urrent, - zero-sequene rely for rdil feeder with trnsformer onneted euse inrush urrents sturte the CT nd then indue flse zero sequene urrent tht trips the rely. The rely must not trip during inrush onditions to ensure the servie ontinuity of the energy nd to prevent internl fult M. Petit is with the Deprtment of nergy (power network group), UPLC, Plteu de Moulon, 992 Gif-sur-Yvette, Frne (e-mil: mr.petit@supele.fr). P. Bstrd mnges the Deprtment of nergy, UPLC, Plteu de Moulon, 992 Gif-sur-Yvette, Frne (e-mil: ptrik.strd@supele.fr). Presented t the Interntionl Conferene on Power ystems Trnsients (IPT ) in Montrel, Cnd on June 9-23, 2 Pper No. IPT - 48 (tripping the trnsformer during n inrush urrent genertes high overvoltge tht my e ritil for the insultor nd then use n internl fult). The inrush urrents lso indue mehnil stress tht n e dngerous for the trnsformer life-time nd then the power network seurity. Mny ppers hve een pulished to study the inrush urrents with three points of view: (i) improve the disrimintion etween fult urrent nd n inrush urrent with the im to prevent flse tripping nd then to improve the energy qulity. everl methods hve een proposed to detet n inrush urrent. A lssil method ompres the mgnitude of the seond hrmoni with the mgnitude of the fundmentl frequeny omponent of the differentil urrent. Aove fixed threshold level (generlly 2 %) n inrush urrent is deteted nd the rely is inhiited. But suh simple lgorithm hs some limittions []. Improvements hve reently een proposed. [2] uses the ngulr reltionship etween the first nd seond hrmonis of the differentil urrent, [3] uses riterion sed on the time vrition of the seond hrmoni of differentil urrent. New methods using wvelet [4] or neurl network oupled with n FFT nlysis [] re lso proposed. (ii) redution the inrush urrents. As they re prolem for the relys reliility solution is to redue them. everl solutions hve een proposed. [6] inreses the trnsient indutne of the primry oil, [7] proposes to use virtul ir gp with the AGW (ir gp winding) tehnique nd [8-] ontrols the swithing instnt. (iii) impt on the mehnil stress. This side effet of the inrush urrent is investigted in [], [2]. The mjor prt of the studies minly fouses on differentil relys. In the present pper we will fous on zero-sequene rely tht protets rdil feeder of MV network with MV/LV trnsformers onneted. Our gol is to disriminte the three following situtions: - fult urrent, - inrush urrent with fult - inrush urrent without fult The rely must trip in the two first situtions.

2 II. DCRIPTION OF TH IMULATD NTWORK The lgorithm hs een tested with the rdil 3-wires MV network desried in fig.. A HV soure (63 kv, 6 MVA) feeds step down trnsformer (63 kv / 2 kv, Yyn, 3 MVA) through 2 km HV line. The HV/MV trnsformer is resistively grounded with R N = 4 Ω. The MV usr feeds two eril feeders: (i) sound feeder onneted to kva hrge (with.9 power ftor) through 2 km eril line. (ii) fulty feeder onneted to kva hrge (with.9 power ftor) nd nine MV/LV trnsformers (2 kv / 4 V, Dyn, 63 kva) t its end. The feeder length is 2 km with the fult t the middle of the line. The mgnetizing sturtion of the MV/LV trnsformers is modeled with non liner indutne put on the LV side. The fulty feeder is proteted y zero-sequene rely (fig. 2) whih mesures the three line urrents on the seondry side of three CTs (2 A / 4 A). The mgnetizing sturtion of the CTs is modeled with non liner indutne put on the primry side (fig. 3). The three rekers re ommnded the rely s lgorithm. All lines re modeled s CP lines ontinuously trnsposed nd power trnsformers (3 legs) with RL oupled models from the BCTRAN routine. The CTs re modeled with -phse idel trnsformers. III. ZRO-QUNC RLAY A zero-sequene rely detets fult to ground s soon s the zero-sequene urrent is ove defined threshold. For eril lines most of fult to ground re trnsient fults, i.e. relosing sequene with 3 ms opening is often enough to ler the fult. But trnsformers onneted to the feeder n indue prolems when the reker is relosed. The trnsformers re-energiztion indues inrush urrents with pek vlues of out ten times the nominl vlue. As the primry windings of the MV/LV trnsformers re delt onneted the rel zero-sequene urrent is null, so the rely should e P_C P_B P_A P2 phse 3 phse 2 phse reker_ommnd P CT_C i_c P9 CT_B i_b i_a lgorithm Fig. 2. Protetive rely with the three CTs, the lgorithm nd the reker s ommnd. Lnonl f Tr_ 2 3 3nF Rse.3 C2 CT_A Rfil.7 i(t) Fig. 3. CT modeling. R se, R fil nd R h re respetively the seondry winding, le link nd hrge resistnes (vlues re in ohms). The totl resistne is R t = R se R fil R h =. Ω intive. But the phse urrents re mesured on the seondry windings of the CTs, while the CT is unsturted: dφct i prim = ise, vse = Rtise = nd φct = Rt ise ( t) dt dt When there is n inrush urrent the pek vlue of i prim is high nd the CT flux φ CT will inrese up to the sturtion, then i se drops to zero. As the inrush urrents of the three phses re dissymmetri (euse the three poles of the reker lose simultneously) the three CT will not sturte t the sme time. One the first CT sturtes the mesured residul urrent is no more null. We n notie tht this flse residul urrent ppers with dely fter the line relosing, this dely is the time efore the first CT sturtes. A flse zero-sequene urrent ppers nd the rely my trip the rekers. To prevent suh ml-opertion, restrint lgorithm using the Hz positive sequene urrent is used..9 P2_C P2_B P2_A Rh imultion Options soure 63 kv, 6 MVA AC 63kVRMLL /_ Z.7,7Ohm trt MTP HV_BU HV_line 2 CP MPLOT Trnsformer Dt BCTRAN model in: trnsfo_3mv_yy_63kv_2kv.pun 63 kv / 2 kv, Yyn 3 MVA p3 p2 p p6 p p4 Trnsformer_HV_MV_Yyn MV_Busr VM?vm A m2 Rely P_C P2_C P_B P2_B P_A P2_A sound_feeder P4_C P4_B P4_A fulty_feeder P3_C P3_B P3_A Fig.. Rdil MV network fed y HV line through 3 MVA trnsformer. The studied rely protets the fulty feeder.

3 IV. RTRAINT ALGORITHM The proposed lgorithm uses the dely etween the positive sequene Hz urrent nd the flse zero-sequene urrent whih is hrteristi of n inrush urrent without fult. If the fult is permnent, the feeder relosing genertes n inrush urrent with fult, nd then there is rel zerosequene urrent simultneously with the positive sequene Hz urrent. The sequene urrents re lulted through 2 ms sliding window. Our lgorithm needs three prmeters: - detetion threshold of the zero-sequene Hz urrent, - detetion threshold of the positive sequene Hz urrent, - threshold vlue for the dely etween the rossings of the previous thresholds. For our exmple we hose ma for the urrents thresholds nd 2 ms for the threshold dely. The lgorithm is represented in fig. 4 with the loks of the MTP-RV lirry. When the zero-sequene urrent eomes higher thn the threshold, the omprtor output (COMP_) is set to nd 2 ms- pulse is generted. It is the sme for the positive sequene Hz urrent. The two pulses re sent to the inputs of XOR logil funtion (). The output of is pulse with equl to the dely etween the threshold rossings of the positive nd zero sequene urrents. If this dely is less thn the dely threshold (2 ms), the AND logil funtion (Fm) genertes pulse tht will open the reker: n inrush urrent with fult is deteted. V. RULT Now let us look t the lgorithm s ehvior to disriminte inrush urrent with fult nd without fult during relosing sequene. A. Inrush urrent without fult The reker is open fter trnsient phse-to-ground fult detetion nd is relosed t t = 43.2 ms. After the relosing the I thres_pos_hz threshold is rossed immeditely, (), nd the I thres_zero_hz threshold is rossed t t = 43.4 ms with ms dely, (2). The ommnd signls in Fig. show tht there is no. Hz positive sequene Hz zero sequene 2 f2 Fm4 = f2 Fm = f2. Fm4 reker relosing Fig.. Commnd signls generted y the lgorithm. Phsors mplitudes of the zero.4 nd positive.4 sequenes.42 urrents tim e re (s).43 in Ampere. No.44 pulse for Fm.4 the reker remins losed. phse urrents (A) reker opening reker relosing phse A phse B phse C i (A) 2-2 instntneous zero sequene urrent Fig. 6. Phse urrents for relosing sequene with trnsient fult. ZRO_Q_Hz P9 Fm Fm4 f2 dely delyed pulse #dely_threshold# dely delyed pulse dely delyed pulse COMP_ COMP_2 Compre 2.2 Compre 2 mgn i i2 i3 threshold #Ithres_zero_Hz# PO_Q_Hz mgn i3 i2 i threshold #Ithres_pos_Hz# i_a i_b i_c Fig. 4. Algorithm to disriminte n inrush urrent. The input prmeters re I thres_pos_hz, I thres_zero_hz nd dely_threshold. In the present pper the prmeters vlues re respetively: ma, ma nd 2 ms.

4 pulse generted y Fm, so the reker remins losed. The phse urrents, during the omplete relosing sequene, re plotted in fig. 6. In the sme figure the instntneous zero sequene urrent mesured y the CTs is plotted. This urrent is similr to the on-site registered dt (fig. 7) reker opening phse A phse B phse C i (A) t phse urrents (A) -2-4 reker relosing reker opening Zero sequene urrent mesured fter rely relosing Fig. 7. instntneous zero sequene urrent mesured y rely fter relosing without fult. The effet of the inrush urrent lerly ppers on these on-site registered dt. B. Inrush urrent with fult The phse-to-ground fult is permnent, the reker is open fter its detetion nd is relosed t t = 43.2 ms. After the relosing the I thres_pos_hz threshold is rossed t t = ms nd the I thres_zero_hz threshold is rossed t t = 43.3 ms with.3 ms dely. Here the fult indues rel zero sequene just fter the relosing. The ommnd signls in Fig. 8 show tht there is pulse is generted y Fm, so the reker re-opens fter 4 ms dely. The phse urrents re plotted in fig. 9 reker relosing Fig. 8. Commnd signls generted y the lgorithm. Phsors mplitudes of the zero nd positive sequenes urrents re in Ampere. Pulse for Fm the reker is re-opened with 4 ms reker dely C. Phse-to-ground fult Hz zero sequene f2 Fm4 Fm Hz positive sequene reker opening The present lgorithm n lso e used to detet phseto-ground fult euse the lultion of the phsors through 2 ms window genertes flse Hz positive sequene during the trnsient regime (fig. ). This sequene urrent rehes the threshold simultneously with the zero sequene. It ws pplied in fig. 6 nd 9 to detet the fult t t = 6 ms. urrents (A) Fig. 9. Phse urrents for relosing sequene with permnent fult Hz zero sequene Hz positive sequene Fig.. Hz zero sequene nd Hz positive sequene during the fult. The urrents re lulted through 2 ms window. VI. CONCLUION The detetion of inrush urrents is n importnt issue for protetion relys mnufturers euse it n generte mlopertions. In this pper we foused on zero-sequene rely tht protets MV eril feeder with MV/LV trnsformers onneted. uh rely n ml-operte due to the sturtion of the CTs whih genertes flse zero sequene urrent nd then trips the reker. A simple method using the dely etween the Hz positive sequene nd the Hz zero sequene urrents is used to disriminte n inrush urrent from fult. This lgorithm needs three prmeters: (i) threshold of the zero-sequene Hz urrent mplitude, (ii) threshold of the positive-sequene Hz urrent mplitude nd (iii) threshold vlue for the dely etween the rossings of the previous thresholds. An inrush urrent with fult or fult lone re hrterized with very short dely etween the two

5 threshold rossing (less thn 2 ms), wheres the dely is higher thn 2 ms for n inrush urrent without fult. This is the riterion used in this pper. The rely ws fully simulted with the new MTP-RV using oth power nd ontrol loks. VII. RFRNC [] B. Ksztenny nd A. Kulidjin "An improved trnsformer inrush restrint lgorithm," 3 rd Annul Conferene for Protetive Rely ngineers. Aville : [2] A. Kulidjin nd B. Ksztenny "New mgnetizing inrush restrining lgorithm for power trnsformer protetion, in Pro. 7 th Int. Conf. Developments in Power ystem Protetion, 2, pp [3] M.. H. Golshn, M. ghin-nejd, A. h nd H. met, A new method for reognizing internl fults from inrush urrent onditions in digitl differentil protetion of power trnsformer, letri Power ystems Reserh, vol. 7,pp. 6-7, ept 24. [4]. Y. Hong nd W. Qin, A wvelet-sed method to disriminte etween inrush urrent nd internl fult, Pro. 2 Int. Conf. Power ystem Tehnology, pp [] T. W. Chn, C. K. Chn nd H. B. Gooi, Detetion of mgnetizing inrush urrent using rtifiil neurl network, Conf. 993 I Region Conf. on Computer, Communition, Control nd Power ngineering, pp [6] C. K. Cheng, T. J. Ling, J. F. Chen,. D. Chen nd W. H. Yng, Novel pproh to reduing the inrush urrent of power trnsformer, I Pro. letri Power Applitions, v., n. 3, 8 My 24, p [7] V. Molrette, J. L. Kotny, J. P. wn nd J. F. Brudny, "Redution of inrush urrent in single-phse trnsformer using virtul ir gp tehnique," I Trns. Mgn.., vol. 34, pp.92-94, July 998. [8] W. N. Leourt, Reduing mgnetizing inrush urrents through the use of new ontrol tehnique for zero voltge turn-on of solid stte relys, in Pro. 44 th Rely Conf., 996, pp 6/-6 [9] J. H. Brunke nd K. J. Frohlih, limintion of trnsformer inrush urrents y ontrolled swithing, prt I: Theoretil onsidertions, I Trns. Power Delivery, vol. 6, pp , April 2. [] J. H. Brunke nd K. J. Frohlih, limintion of trnsformer inrush urrents y ontrolled swithing, prt I: Applitions nd performne onsidertions, I Trns. Power Delivery, vol. 6, pp , April 2. [] A. A. Adly, Computtion of inrush urrent fores on trnsformer windings, I Trns. Mgn., vol. 37, pp , July 2. [2] M. teurer nd K. J. Frohlih, The impt of inrush urrents on mehnil stress of high voltge power trnsformer oils, I Trns. Power Delivery, vol. 7, pp. -6, Jn. 22. VIII. BIOGRAPHI Mr Petit ws orn in Deville les Rouen (Frne) on Otoer 2, 972. He is former student of the ole Normle upérieure de Chn (south of Pris) nd reeived Ph-D degree in 22 from the University Pris XI Orsy. He joined UPLC in 23 s n ssistnt professor nd works in the Power Network group. Ptrik Bstrd is presently with RNAULT sine 2. He ws previously professor t UPLC, Frne, where he mnged the Deprtment of energy. His min reserh tivities were out power relying, power system simultion nd power system optimiztion in n open-mrket ontext. He grduted from UPLC in 988. He reeived Ph-D. degree in power system engineering in 992 from the University of Pris, Frne.