Optimal Placement of Wind Turbine DG in Primary Distribution Systems for Real Loss Reduction

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1 Optmal Placemet of Wd Turbe DG Prmary Dstrbuto s for Real oss Reducto Pukar Mahat, Weerakor Ogsakul ad Nadaraah Mthulaatha Abstract Optmal placemet of wd geerators s essetal, as approprate placemet may crease the system losses. Ths paper proposes a methodology for fdg the optmal sze ad locato for coectg wd type dstrbuted geerato (DG prmary dstrbuto systems for mmzg real power loss the system. The characterstc of wd turbe geerato s represeted by a aalytcal expresso, whch s used to solve DG szg ad placemet problem. Exact loss formula s used to fd the loss the system. The proposed methodology s tested 33-bus ad 69-bus radal dstrbuto systems. The effect of optmal DG placemet o system voltage profle ad brach currets s also vestgated ad reported. Keywords Dstrbuto load flow, exact loss formula, loss mmzato, optmal placemet ad szg, wd turbe dstrbuted geerato.. INTRODUCTION Dstrbuted or dspersed geerato may be defed as a geeratg resource, other tha cetral geeratg stato, that s placed close to load beg served, usually at customer ste. It may be coected to the supply sde or demad sde of meter. It ca be reewable sources based mcro hydro, wd turbes, photovoltac, etc or fossl fuel based fuel cells, recprocatg eges, mcro turbes, etc. I term of sze, DG may rage from few klowatts to over 00 megawatts []. The share of DGs power system world wde s creasg ad ther cotrbuto the future power system s expected to be eve more []. Eergy polces worldwde are ecouragg stallato of DGs both trasmsso ad dstrbuto etworks alog wth large scale power geeratg plats. The geeral belef s that the future of the power geerato wll be DGs. But the fact s that the dstrbuto systems were ot plaed to support the stallato of actve power geeratg uts them. DGs come wth opportutes as well as challeges. They, oe had, are expected to be the soluto of most of the power system problems whle, o the other had, they are addg ew problems. Ther grd coecto, prcg, chage protecto scheme are the ame of the few. Stll we ca reap maxmum beeft from ths ew power geerato techology f t s hadled properly. Hece, utltes ad dstrbuto compaes eed tools to place small geeratg uts ther dstrbuto systems. The eed s eve more essetal whe the DG s wd turbe as wd turbe teds to cosume reactve power for every ut of real power produced. However, oe has to cosder the avalablty of eough wd speed as well. A ear optmal placemet techque to reduce the system loss has bee preseted [3] usg B loss coeffcet. The buses are raked accordg to ther loss sestvty ad sze of DG s foud stepwse maer. Ths method s bascally cocered wth fdg the optmal locato of DG ad loss sestvty method always does ot gve the accurate result. Geetc algorthm (GA based dstrbuto geerato placemet techques to reduce overall power loss dstrbuto system are preseted [4]-[7] but the problems wth GA are that t s Pukar Mahat s wth the Asa Isttute of Techology, Eergy Program, P.O.Box: 4, Klog uag, Pathumtha, 0, Thalad (emal: pukarmahat@hotmal.com, phoe: , Fax: , correspodg author Weerakor Ogsakul s wth the Asa Isttute of Techology, Eergy Program, P.O.Box: 4, Klog uag, Pathumtha, 0, Thalad (e-mal: ogsakul@at.ac.th Nadaraah Mthulaatha s wth the Asa Isttute of Techology, Eergy Program, P.O.Box: 4, Klog uag, Pathumtha, 0, Thalad (e-mal: mthula@at.ac.th computatoally tesve ad suffers from excessve covergece tme ad premature covergece. Hereford rach algorthm s used to optmally locate the DG to reduce the system overall real power loss uder the costrat of the total ecto of stalled dspersed geerato [8]. Smlar to the GA based methods, ths method s also computatoally demadg though t addresses the ssue of premature covergece ad has the ablty to search for a better optmal soluto. I [9], the optmal locato to place a DG, wth uty power factor, a radal or looped system s foud whle mmzg the loss. Ths techque s bascally cocered wth fdg the optmal locato ot the optmal sze. I ths paper smlar methodology as [0] has bee used for optmal wd turbe DG placemet for mmzg real power loss prmary dstrbuto systems. The proposed methodology ca be used to fd the coectg locato of oe wd plat at a tme for maxmum loss reducto. Aalytcal expressos have bee used to fd the optmal sze for every locato ad to fd the best locato amog them.. PROPOSED METHODOOGY ACTS Ths secto presets the problem formulato ad the soluto related to the optmal DG sze ad locato. Whe the DG supples real power but absorbs reactve power, the bus where the DG s stalled has to be treated as a load bus. Most of the wd turbes have the smlar characterstc, so the locato at whch they are coected has bee treated as load buses whle performg load flow aalyss. The obectve of ths placemet techque s to mmze the real power loss. Mathematcally, the obectve fucto ca be wrtte as: M P ( s.t. P G PD + P ( Where, P s the real power loss the system, ad P G ad P D are ts power geerato ad demad, respectvely. I addto, real power loss the system ca be calculated usg equato (3, kow as exact loss formula [], f the system operatg codto s kow. P A ( PP + Q Q + B ( Q P PQ (3 where, R Cos A VV R S B VV ( δ δ ( δ δ (4

2 ad, P ad Q are et real ad reactve power ecto bus, respectvely R s the le resstace betwee buses ad V ad δ are the voltage ad agle at bus, respectvely For wd turbes, ducto geerators are used to produce real power ad reactve power wll be cosumed the process []. The amout of reactve power they cosume s a fucto of the actve power output. The reactve power cosumed by a DG (wd turbe geerator a smple form ca be represeted by equato (5 [3]: Q DG - ( P DG (5 Now the real loss equato ca be wrtte as P A ( PDG PD P + ( 0.04 P Q DG D Q B + ( 0.04 P Q ( DG D P PDG PD Q The ecessary codto for mmum loss s: or, let, DG DG (6 P A ( P 0.08 P Q + B ( 0.08 P P Q 0 P DG A PDG PD PDG( PDG + QD + ( AP BQ 0.08PDG ( AQ + B P 0 X Y ( A P BQ ( AQ + B P Equato (8, thus, ca be wrtte as [ ] ( A PDG + PDG.004A AQ D 0.08 Y + X A PD 0 (0 If we solve the above equato for P DG, we wll kow the amout of real power that the wd turbe has to produce at varous locatos so as to mmze the real loss. Ths wll solve the szg problem ad placemet problem s solved by comparg the losses by puttg DG of correspodg optmal szes at varous locatos. The bus at whch the total loss s mmum ad correspodg sze wll be the optmal locato ad sze, respectvely. The methodology ca be descrbed followg steps: Step : Use the test system data ad ru the dstrbuto load flow to fd the base case steady state operatg (7 (8 (9 8 0 Step : Step 3: Step 4: Step 5: Step 6: codto of the system. Fd DG s optmal real power producto ad correspodg reactve power cosumpto, for all possble locatos, usg equatos (0 ad (5, respectvely. Select a locato ad correspodg DG sze. The, update the real ad reactve power ecto at that locato ad calculate the ew approxmate system real power loss. Repeat Step (3 for all possble locatos. The locato ad the correspodg sze of the wd turbe DG that wll gve the lowest system real loss wll be the optmal locato ad sze, respectvely. Ru the dstrbuto load flow wth the optmal sze of DG at the optmal locato ad fd the exact system real loss. I step (3, we update the real ad reactve power ecto of the bus where the DG of correspodg optmal sze s stalled ad keep other system varables (voltages ad agles of all the buses as the base case. Usg the base case values of the voltages ad agles ad updated values of the real ad reactve power ecto at the selected bus, we calculate the real loss. The losses calculated ths maer, hereafter, wll be called as approxmate losses. We ca also fd the losses by usg the updated values of all system varables. Updated values ca be obtaed by the rug the load flow wth a wd turbe DG. osses calculated ths maer, hereafter, wll be called as exact losses. Although, there wll be chages system codtos oce there s a ew stallato of wd turbe geerator, the chage wll ot be very sgfcat. Furthermore, we eed to fd losses ust to of fd the best locato ad results show that the system exact ad approxmate losses, wth correspodg optmal szed DG stalled at varous locatos, wll follow the same tred. Hece, by usg the approxmate losses rather tha the exact losses, we ca save sgfcat amout of computato tme as we eed to ru the load flow oly twce whereas we would have eeded to ru t as may tmes as the umber of buses had we preferred to fd the exact losses each tme. 3. NUMERICA RESUTS AND DISCUSSIONS The methodology s tested two radal dstrbuto test systems. The frst oe s the 33-bus radal system wth a total load of 3.7 MW ad.3 MVar. It s a modfed form of the oe used [4]. The total real power loss s.4346 kw whle the total reactve power loss s kvar. The sgle le dagram of the modfed 33-bus test dstrbuto system s show Fgure. The secod test system s the 69-bus radal system wth a total load of 3.80 MW ad.69 MVar. It s a modfed verso of the system used [5]. The total real ad reactve power losses are kw ad kvar, respectvely. The sgle le dagram of the modfed 69-bus test dstrbuto system s show Fgure. I both the test systems, Bus No. s the source ode coected to the trasmsso system whle Brach refers to the brach coectg Bus No. to Bus No Fgure : Sgle e Dagram of the 33-Bus Radal Dstrbuto

3 Fgure : Sgle e Dagram of the 69-Bus Radal Dstrbuto Based o the proposed methodology, the optmal DG szes for all the buses are foud terms of ther optmal real power producto ad correspodg reactve power cosumpto. The optmal rage of real power producto from the wd turbe DG s ragg from 0.33 MW to 3.8 MW for the 33-bus system whle the rage for the 69-bus system s ragg from 5 kw to 3.9 MW. Fgure 3 shows the optmal real power that a wd turbe DG should produce whe t s located at varous locatos, for the 33-bus system, so as to mmze the real power loss the system whle Fgure 4 s for the 69-bus system. Fgure 3: Optmal Real Power Producto for the 33-Bus Fgure 5 shows the ew system real power losses, the 33-bus system, whe we stall wd turbe DGs of correspodg optmal szes at varous locatos. For Bus No., the optmal real power producto ad correspodg reactve power cosumpto, to mmze the loss, are 3.83 MW ad.09 MVar, respectvely. Thus, the loss correspodg to Bus No., the Fgure 5, s the ew system loss whe we stall a wd turbe DG, at Bus No., that wll produce 3.83 MW of real power ad cosumes.09 MVar of reactve power. Smlarly Fgure 6 shows the ew system losses, the 69-bus system, wth optmal DG stallato at varous locatos. Fgure 4: Optmal Real Power Producto for the 69-Bus As stated earler, Fgures 5 ad 6 show that the approxmate ad exact losses follow the same tred. Furthermore, the locato whch gves the mmum approxmate loss wll also gve the mmum exact loss. As the losses are calculated ust to solve the locato problem, we ca save much of the computato tme usg approxmate losses ad that also wthout compromsg ay accuracy detfyg locato. We ca also coclude from the Fgures 3 ad 5 that the optmal locato for a wd turbe DG, for the 33-bus system, s Bus No.. The wd turbe DG located at Bus No. should produce.45 MW of real power to make the system real power loss mmum. It wll, tur, cosume 0.74 MVar of reactve power. Smlarly, from Fgures 4 ad 6, we ca coclude that, for the 69-bus system, a wd turbe DG producg.78 MW of real power should be stalled at Bus No. 56 to make the real power loss the system mmum. It wll, tur, cosume 0.63 MVar of reactve power. Fgures 5 ad 6 show that optmal DG placemet ca help loss reducto. But, terestgly wth wd turbe DGs, there wll be some locatos the system, whch wll ot have ay DG sze that ca reduce the loss the system. These locatos wll deped upo the system characterstcs as well as the characterstc of power geerato from the wd turbe DG.

4 . Real Power osses (kw Approxmate osses Exact osses 3 Fgure 5: Exact Vs Approxmate osses the 33-Bus Approxmate osses Exact osses Table : Bus Rakg based upo the oss Reducto Capablty for the 69-Bus DG Sze Power oss oss Reducto Bus Real Reactve Real Reactve No: MW MVar (kw (kvar (% (% Improvemet voltage profle ad reducto brach currets, the 33-bus system, ca be otced from Fgures 7 ad 8, respectvely. The lowest bus voltage before the DG was p.u. at Bus No. 33 ad t s p.u. after optmal DG stallato, though stll at Bus No. 33. Smlarly, the curret the Brach has reduced from p.u. to p.u Base Case Voltage Voltage after Optmal DG Istallato osses (kw Real Power Bu s Vo ltages p.u Fgure 6: Exact Vs Approxmate osses the 69-Bus Tables ad gve the lst of the 5 best locatos to place DG terms of ther loss reducto capablty alog wth the correspodg optmal sze for the 33-bus ad 69-bus systems, respectvely. Table : Bus Rakg based upo the oss Reducto Capablty for the 33-bus DG Sze Power oss oss Reducto Bus Real Reactve Real Reactve No: MW MVar (kw (kvar (% (% Brach Curret p.u Fgure 7: Bus Voltages Before ad After Optmal DG Istallato the 33-Bus Base Case Brach Curret Brach Curret after DG Istallato Bus No Fgure 8: Brach Currets Before ad After DG Optmal Istallato the 33-Bus 3 s Volt s p.u. Bu age Base Case Voltage Voltage after Optmal DG Istallato Fgure 9: Bus Voltages Before ad After Optmal DG Istallato the 69-Bus

5 Base Case Brach Curret Brach Curret after DG Istallato Brach Curret p.u Bus No Fgure 0: Brach Currets Before ad After Optmal DG Istallato the 69-Bus Improvemet voltage profle ad reducto brach currets, the 69-bus system, ca be otced from Fgures 9 ad 0, respectvely. The lowest bus voltage before the DG was p.u. at Bus No. 64 ad after the optmal DG stallato, the lowest bus voltage s stll at Bus No. 64 but the value has mproved to p.u. Smlarly, the curret the Brach has reduced to p.u. from p.u. 4. CONCUSIONS The paper presets methodology to place wd turbe DG optmally prmary dstrbuto systems wth the vew of mmzg the real power loss the system whle cosderg ts characterstc. The methodology s fast ad accurate determg the sze ad locato ad furthermore, a look up table ca be created wth oly oe power flow calculato ad the table ca be used to restrct the sze of DGs at dfferet buses, wth the vew of mmzg total losses. The paper assumes that the DG s stalled at oe locato at a tme, whch s a vald assumpto. Ths paper however does ot cosder the other beefts of DG as well as ecoomcs of t. REFERENCES [] Aclerma, T. Adersso, G. ad Soder,. 00. Dstrbuted Geerato: a Defto, Vol. 57, No. 3, pp [] CIGRE CIGRE Techcal Brochure o Modellg New Forms of Geerato ad Storage Tf , Retreved February 3, 005, from pdf [3] Grff, T. Tomosovc, K. Secrest D. ad aw A Placemet of Dspersed Geeratos s for Reduced osses, I Proceedg of 33rd Hawa Iteratoal Coferece o Sceces, 000, Hawa [4] Mthulaatha, N. Oo, T. ad Phu,.V Dstrbuted Geerato Placemet Power Dstrbuto Usg Geetc Algorthm, Thammasat It. J. Sc., Vol. 9, No. 3, pp [5] Km, K. H. ee, Y. J. Rhee, S. B. ee, S. K. ad You, S. K. 00. Dspersed Geerato Placemet Usg Fuzzy- GA Dstrbuto, I Proceedgs of IEEE Power Egeerg Socety Summer Meetg, Chcago, Vol. 3, pp [6] Slvestr, A. Berzz, A. ad Buoao, B Dstrbuted Geerato Plag Usg Geetc Algorthm, I Proceedg of Iteratoal Coferece o Electrc Power Egeerg, Budapest [7] Carpell, G. Cell, G. ad Russo, A. 00. Dstrbuted Geerato Szg ad Stg Uder Ucertaty, I Proceedgs of IEEE Porto Power Tech, Porto [8] Km, J. O. Nam, S.W. Park, S. K. ad Sgh, C Dspersed Geerato Plag Usg Improved Hereford Rach Algorthm, Electrc Power s Research, Vol. 47, pp [9] Wag, C. ad Nehrr, N.H Aalytcal Approaches for Optmal Placemet of Dstrbuted Geerato Source Power, IEEE Trasacto o Power, Vol. 9, No. 4, pp [0] Acharya, N. Mahat, P. ad Mthulaatha, N A aalytcal approach for DG allocato prmary dstrbuto etwork, Iteratoal Joural of Electrcal Power & Eergy s (Accepted [] Elgerd, I.O. 97. Electrc Eergy Theory: a Itroducto, McGraw Hll [] Erms, M. Erat, H. B. Demrekler, M. Sarbatr, B. M. Uctug, Y. Sezer M. E. et al. 99. Varous Iducto Geerator Scheme for Wd Power Electrcty Geerato, Electrc Power Research, Vol. 3, pp [3] DTI Network Performace Beefts of Eergy Storage for a arge Wd Farm, Retreved February 7, 005, from pdf [4] Kashem, M.A. Gaapathy, V. Jasmo, G.B. ad Buhar, M.I. A Novel Method for oss Mmzato Dstrbuto Networks, I Proceedgs of Iteratoal Coferece o Electrc Utlty Deregulato ad Restructurg ad Power Techologes, pp [5] Bara M.E. ad Wu, F.F Optmal Szg of Capactor Placed o Radal Dstrbuto s, IEEE Tras PWRD, Vol-4, pp