Economic pricing techniques for transmission network in deregulated electricity market

Transcription

1 Economc prcng technques for transmsson network n deregulated electrcty market Shakashraf al 1, K.Vmala kumar 2 P.G.Scholor, E.E.E Department, J.N.T.U.A College of Engneerng,Pulvendula,Kadappa,Inda 1 Assstant professor, E.E.E Department, J.N.T.U.A College of Engneerng,Pulvendula,Kadappa,Inda 2 Abstract: The am of deregulaton s to ntroduce an element of competton nto electrcal energy delvery and thereby allow market forces to prce energy at low rates for the customer and hgher effcency for the supplers. The necessty for deregulaton s to provde cheaper electrcty, to offer greater choce to the customer n purchasng the economc energy, to gve more choce of generaton and to offer better servces wth respect to power qualty.e. constant voltage, constant frequency and unnterrupted power supplyths paper provdes a methodology to apporton the cost of the transmsson network to generators and demands that use t. How to allocate the cost of the transmsson network s an open research ssue as avalable technques embody mportant smplfyng assumptons,whch may render controversal results. In ths paper three technques namely Z bus method, Z bus avgmethod and Relatve Electrcal Dstance (RED) method for the network cost allocaton s compared. It has been successfully appled on an IEEE 24 bus-relablty Test System (RTS) and the results obtaned are compared. Keywords: Transmsson network cost allocaton, actve power flow, generator cost contrbuton, load cost contrbuton, Z bus,z bus avg and RED. I. INTRODUCTION Deregulaton word refers to un-bundlng of electrcal utlty or restructurng of electrcal utlty and allowng prvate companes to partcpate. The am of deregulaton s to ntroduce an element of competton nto electrcal energy delvery and thereby allow market forces to prce energy at low rates for the customer and hgher effcency for the supplers.in the tradtonal pro rata method [1], [2] bothgenerators and loads are charged a flat rate per megawatthour, dsregardng ther respectve use of ndvdual transmsson lnes. Flow-based method [3] estmates the usage of the lnes by generators and demands and charges them accordngly. Some flow-based methods use theproportonal sharng prncple [4], [5], whch mples thatany actve power flow leavng a bus s proportonally madeup of the flows enterng that bus, such that Krchhoff scurrent Law s satsfed. Other methods that use generatonshft dstrbuton factors [6] are dependent on the selectonof the slack bus and lead to controversal results. The usagebasedmethod reported n [7] and [8] uses the so-calledequvalent blateral exchanges (EBEs). II. PROBLEM STATEMENT A. Background of Z bus and Z bus avg technque Fgure 1. Π equvalent crcut of lne secton jk Consder the complex power flow S JK computed at bus j and flowng through the lne connectng bus j to bus k asshown n Fgure 1.As the power flow soluton s known, weselect the drecton of the complex power flow so that P JK >0 The complex power flows jk s S jk = V J I jk (1) Ths complexpower flow equaton can be wrtten as n S jk = V j =1( a jk I ) n = V j (a =1 jk I ) (2) sh Here a jk = (Z j Z k )Y jk + Z j Y jk (3) We know that the power flow through any lne s P jk = Real {V j a jk I } (4) B. Transmsson cost allocaton usng Z bus U jk = P jk (4) Total usage of the lne jk s n U jk = =1 U jk (5) If bus contans only generaton, the usage allocated to generaton pertanng to lne jks G U jk = U jk (6) If bus contans only demand,the usage allocated to demand pertanng to lne jks D U jk = U jk (7) For the sake of smplcty and for each lne, total annualzed lne cost n $/h, C jk, whch ncludes operaton, mantenance and buldng costs s consdered. The correspondng cost rate for lne jks then r jk = C jk /U jk (8) In ths way, the cost of lne jkallocated to the generator located at bus s G G C jk = r jk U jk (9) Copyrght to IJIREEICE

2 Smlarly, cost of lne jkallocated to the demand located at bus s D D C jk = r jk U jk (10) Fnally, the total transmsson cost of the network the generator located at a bus s C G = j,k єωl r jk U G jk (11) Smlarly, cost of lne jkallocated to the demand located at bus s C D D = j,k єωl r jk U jk (12) Equaton (2) s wrtten n such a manner that P jk 0, that s, n the drecton of the actve power flows. However, (2) can also be wrtten n the drecton of the actve power counter-flows, whch leads to dstance parameters a jk. It s correct to wrte Equaton (2) n both the ways. However, (3) shows that dstance parameters are not generally symmetrcal wth respect to lne ndexes,.e., a jk a kj,whch results n dfferent usage allocatons dependng on whether (2) s wrtten n the drecton of the actve powerflows or counter-flows. Now, to address these two types of power flows, twoz bus based technques are used. The frst one s denoted byz bus and s based on (2) wrtten n the drecton of the actve power flows. Ths s a common way as the actual actvepower flows drectons are used. Ths selecton generallyresults n hgher usage allocaton to generators versusdemands. The second technque denoted by Z bus provde the average value of allocated cost (usage) usng the Z bus technque wth (2) wrtten n the drecton of the actvepower counter-flows. Ths technque smoothens the trend ofallocatng hgher network usage to generators versusdemands. C. Background of RED technque Consder a system where n s the total number of buses wth 1, 2... g, where g s the number of generator buses and g + 1,..., n, remanng (n - g) are the load buses. For a gven system, the network admttance matrx s gven by I G = Y GG Y GL V G (13) IL Y LG Y LL VL Where I G,I L and V G,V L represent complex current and voltage vectors at the generators and load nodes. Y GG, Y GL, Y LG and Y LL are correspondng portons of network Y-bus matrx I G = Y GG V G + Y GL V L (14) I L = Y LG V G + Y LL V L (15) Pre-multplyng (23) by [Y LL ] 1 V L = Y 1 LL I L Y 1 LL Y LG V G (16) Substtutng [ V L ] n (14), we obtan below equaton no(17) I G = Y GG V G + Y GL Y 1 LL I L Y 1 LL Y LG V G From the equatons (16) and (17) can be wrtten as V L = Z LL F LG I L I (17) G K GL Y GG V G F LG = Y 1 LL Y LG Where K LG = Y GL Y 1 LL = Y GG Y GL Y 1 LL Y LG Y GG avg The elements of [F LG ] matrx are complex. Its columns correspond to the generator bus numbers and rows correspond to the load bus numbers. Ths matrx gves the relaton between load bus and source bus voltages. Ideal generaton proportons are obtaned from abs F LG matrx, also known as desred generaton proportons matrx [D LG ] as D LG = abs F LG (18) D LG ] gves the nformaton about the locaton of load nodes wth respect to generator nodes, whch s popularly termed as RED. The [RED] s obtaned from the [D LG ] matrx as RED = M D LG (19) Where, M s the unty matrx of sze L X G, G s the number of generator buses and L s the number of load buses. D. Evaluaton of the power contract transmsson matrx and transmsson cost matrx Evaluaton of the power contract transmsson matrx and transmsson cost matrxthe power contract transmsson matrx [P LG ] s calculated from the transacton detals between the generatorand the load from whch C LG transmsson cost matrx scalculated usng the followng expresson C LG = X + RED (20) where the transmsson charges are drectly proportonal to the relatve electrcal dstances and t s assumed that the charges for the consumers are Rsx. The transmsson charges are calculated by each element of C LG matrx multpled by the correspondng element of P LG matrx. III. IMPLEMENTATION AND RESULT All the three methodologes are compared by testng t on a standard IEEE 24 bus relablty test system shown n fg.2. A.Z-bus Technque Fg. 2 RTS 24 Bus System Copyrght to IJIREEICE

3 TABLE I. GENERATOR COST CONTRIBUTIONS C 0 (k,) IN P jk >0 DIRECTION OF Z bus TECHNIQUE LINE/ GEN GEN2 GEN7 GEN13 GEN15 GEN16 GEN18 GEN21 GEN22 GEN23 GEN Usng Equaton No 2, the cost of each lne allocated to the load at varous buses s computed.b.z bus Method The cost of each lne allocated to the load and the generator located at varous buses are calculated as per the dscusson made earler for Z bus method TABLE II. COMPARISON OF BOTH Z bus AND Z avg bus TECHNIQUES Z bus Technque avg Technque Z bus CG avg Bus No. CG CD TOTAL COST n $ n $ In $ In $ In $ Copyrght to IJIREEICE CD avg TOTAL COST avg In $

4 The above table gves the nformaton about the cost allocated to dfferent generators and loads for IEEE RTS 24bus system for the Z bus based technques. Though Z bus the methods yeld the same total transmsson cost.e TOTAL COST = $ , t s nferred that the Z bus technque allocates more usage to generators rather than Demands and smlarly allocates most of the cost to generators compared to demands. TheZ bus technque avods the allocatng most of the cost to generators than demands. D.RED method. Usng Equaton No 28, the desred load sharng/generaton schedulng for the standard IEEE 24 bus RTS s calculated and s shown n Table III. All schedules are shown n MW wth an assumpton of same load of 250MW at each load bus. Load Bus Power drawn from each Generator No G1 G2 G7 G13 G15 G16 G18 G21 G22 G23 Total Load (MW) Total E. Evaluaton of Transmsson Charges Total Generaton of Generator 1 = MW Total Generaton of Generator 2 = MW Total Generaton of Generator 7 = MW Total Generaton of Generator 13 = MW Total Generaton of Generator 15 = MW Total Generaton of Generator 16 = MW Total Generaton of Generator 18 = MW Total Generaton of Generator 21 = MW Total Generaton of Generator 22 = MW Total Generaton of Generator 23 = MW Therefore, the total Generaton cost = INR The Transmsson charges are consdered as 10% of the Generaton charges. Therefore, Transmsson Charges = C LG Transmsson Charges when evaluated come to approxmately 10% of the Generaton Charges. Here, n ths case, the loss whch has to be contrbuted by each generated s neglected. So the total amount of actve power to be generated and transmtted by each generator to meet Copyrght to IJIREEICE

5 P LG herefore the total transmsson P LG X C LG shown n Table IV. It s to note that the authors have calculated only the transmsson basc charges by RED method. Therefore, the Total Transmsson Cost obtaned wll be the sum of all the elements of the above matrx = INR % of the Generaton Charges. P LG X C LG meetng a load)*(cost/mw n transferrng the sad share (power) for the dstance between ther locaton). Hence, there s no need of any detals for Table IV (row /column wse) TABLE IV. EVALUATION OF TRANSMISSION BASIC CHARGES IV. CONCLUSION In ths paper, three transmsson network cost allocaton methodologes are compared usng standard 24 bus RTS. A complete analyss wth a comparatve study has been made on all the three technques.table I provdes the transmsson cost allocaton to generators by Z BUS technque. Table II shows the total transmsson cost allocaton for all the generators and demands by the frst two technques.from table II, t s nferred that both the above methods allocate most of the costs for usng lne 23 to generators 21, 22, and 23. Ths s because all the generators are electrcally close to that lne, and ther productons are comparatvely hgh.the RED method allocates the transmsson charges based on the relatve locaton of load nodes wth respect to the generator nodes. Ths method s conceptually smple and can be mplemented usng the network confguraton and generaton/load condtons n a day-to-day operaton of power systems. The man advantage of ths method les n ts applcablty to consder multple contracts/transactons smultaneously. Comparng the overall transmsson cost obtaned n all the three technques, RED method s very accurate n estmatng and allocatng the transmsson cost n the transmsson prcng scheme. From the results, t s also found that RED method s very effectve n transmsson cost allocaton..references [1] M. Ilc, F. Galana, and L. Fnk, Power Systems Restructurng: Engneerng and Economcs Norwell, MA: Kluwer, [2] J. W. M. Lma, Allocaton of transmsson fxed rates: An overvew, IEEE Trans. Power Syst., vol. 11, no. 3, pp , Aug [3] J. Balek, Topologcal generaton and load dstrbuton factors for supplement charge allocaton n transmsson open access, IEEE Trans.Power Syst., vol. 12, no. 3, pp , Aug [4] S. Krschen, R. N. Allan, and G. Strbac, Contrbutons of ndvdual Generators to loads and flows, IEEE Trans. Power Syst., vol. 12, no. 1,pp , Feb [5] W. Y. Ng, Generalzed generaton dstrbuton factors for power system securty evaluatons, IEEE Trans. Power App. Syst., vol.pas-100, pp , Mar [6] D. Galana, A. J. Conejo, and H. A. Gl, Transmsson network cost allocaton based on equvalent blateral exchanges, IEEE Trans. Power Syst., vol. 18, no. 4, pp , Nov [7] H. A. Gl, F. D. Galana, and A. J. Conejo, Multarea transmsson network cost allocaton, IEEE Trans. Power Syst., vol. 20, no. 3, pp , Aug [8] J. Conejo, F. D. Galana, and I. Kockar, Z-bus loss allocaton, IEEE Trans. Power Syst., vol. 16, no. 1, pp , Feb [9] R. Berger and V. Vttal, Power Systems Analyss, 2nd ed. Englewood Clffs, NJ: Prentce-Hall, [10] Relablty Test System Task Force, The IEEE relablty test system 1996, IEEE Trans. Power Syst., vol. 14, no. 3, pp , Aug ACKNOWLEDGMENT The authors acknowledge the support provded by the K.vmalakumar,Assstant professor, J.N.T.U.A.C.E.P, Pulvendula, INDIA for carryng out ths work Copyrght to IJIREEICE