Development of TIF for transaction cost allocation in deregulated power system

Transcription

1 ISSN (Onlne) ISSN (Prnt) Development of TIF for transacton cost allocaton n deregulated power system Noolu.Narendra Reddy 1, Kurakula.Vmala Kumar P.G. Scholar, Department of EEE, JNTUA College of Engneerng Pulvendula, Andhra Pradesh, Inda 1 Asst. professor, Department of EEE, JNTUA College of Engneerng Pulvendula, Andhra Pradesh, Inda Abstract: In deregulated power system due to the ncrease of power transactons n transmsson open access the transmsson cost allocaton s one of the maor problems. For each transacton the Transacton Impact Factors (TIFs) are developed for the allocaton of the transmsson transacton costs. The transmsson Impact Factor gves the nformaton about the real power flow n the transmsson lnes wth the transacted power. Ths logcal method provdes the mpact of the lne flows wthout runnng power flow solutons when the amount of transacted power changes n real tme. Ths proposed method s evaluated by consderng blateral and multlateral transactons. The results comng from the proposed method s compared wth Megawatt Modulus (MM) method on sample sx bus and IEEE 30 bus system. Key words: Deregulaton, Cost allocaton, Transmsson Impact Factors, Blateral transacton, Multlateral transacton. I.INTRODUCTION In ntegrated system, wheelng transactons have been accounted for a small porton of the overall transmsson network capacty usage. However, recent trends towards uundlng of electrc servces have resulted n renewed nterest n prcng of transmsson servces, partcularly to the wheelng transactons. The cost components [1] for provdng transmsson servces are operatng cost, opportunty cost, renforcement cost and exstng system cost. Dependng upon the type of the transmsson transacton one or all the above mentoned cost components are ncluded n the prcng scheme. Transmsson prcng s broadly classfed [] as embedded (rolled-n) transmsson prcng, margnal transmsson prcng and composte transmsson prcng. In embedded prcng (Postage Stamp Method, Contract Path Method, MW-Mle Method) the cost for buldng nfrastructure, operatng and mantenance costs are ncluded. Margnal cost of a transmsson transacton s defned as the cost of accommodatng a margnal ncrease (of say one KW) n the transacted power. Otherwse the margnal transmsson prcng s nothng but a cost allocated to the new customer. Composte prcng scheme nclude the features of above two methods. All type of usage based transmsson cost allocaton schemes requre accurate knowledge of change n power flowcaused by the transacton. The mpact of power flow n the lne can be calculated by electrcty tracng methods [3,4]. A topologcal approach to fnd the share of each generator and load n every power flow s provded n [3]. Thstopologcal generaton and load dstrbuton factors are always postve but t requres nverse of a matrx of theorder equal to the network nodes. Contrbuton of generator and load on the lne flow can also be determned bydefnng set of domans, commons and lnks [4]. The transmsson cost allocaton method based on equvalentblateral exchanges [5] states that each demand s suppled by a fracton of each generator unformly dvded amongall generators. But ths method uses dc power flow soluton. A methodology based on crcut theory [6] uses thecontrbutons of the nodal currents to lne power flows to apporton the usage of the lnes. Dfferent cases of-mle method s dscussed n [7]. In order to meet the system relablty, stablty and securty crtera all the market partcpants have to pay for the actual capacty use and for the addtonal reserve [8]. Megawatt Modulus (MM) method ensures recovery of all transmsson costs by replacng the crcut capactes by the sum of absolute power flows caused by all agents. Dfferent usage based transmsson cost allocaton methods are summarzed n [9] and concludes that fxed transmsson costs determned by dfferent algorthms are qute smlar. The choce of algorthms used for the evaluaton of transmsson usage depends manly on the requrements and the market structures. The mpact of power flow n all the lne n a network due to partcular transacton s usually determned by power flow soluton. In conventonal methods, the lne flow mpacts are calculated by executng repeated power flows by Newton Raphson (NR) method for varyng magntude of power transacted whch s a tme consumng process. To smplfy the evaluaton of power flow mpact, the lne flows are related wth the power contract magntude by the factor called Transacton Impact Factor (TIF). Once the TIF s evaluated, then the power flow mpacts can be obtaned by multplyng t wth the transacted real power between the partes. II. DERIVATION OF TRANSACTION IMPACT FACTOR The senstvty of real power flow n the lne m-n when one megawatt of power s transacted between seller bus andbuyer bus s known as. It means that, f one megawatt of power s nected at bus and extracted at bus then TIF m-n s the power flow mpact of the lne m -n due to ths transacton. The change n power flow n lnem-n can be wrtten as the sum of mpact of power flow due to all sellers nvolved n that transacton as, = Copyrght to IJIREEICE 79 =1 (1)

2 ISSN (Onlne) ISSN (Prnt) where, s the mpact of power flow n lne m-n due to th seller and ns s the number of sellers nvolved nthat transacton. Further the mpact of power flow P m n can be wrtten as sum of mpact due to transactoetween seller bus and buyer bus ( ) P m n = =1 () Where s the number of buyers, Equaton () s multpled and dvded by the magntude of real powertransacted (P )between seller bus and buyer bus = m =1 P P (3) WC t = C m n Alllnes t P 0 + TIF t P m n P m n (8) B.Cost allocaton to users In blateral transacton, the costs have to be allocated to both seller and buyer accordng to ther usage of the network. The proportonal sharng of the cost to seller and buyer wll dffer for dfferent structure. For the case of50% share to seller and 50% share to buyer, the seller Wheelng Charge and Buyer Wheelng Charge n $/hr for thetransacton t are gven by, SWC t = WC t andbwc t = WC t (9) Smlarly for 30% share to seller and 70% share to buyer the followng formulae are used, TIF can be defned as the rato of change n real power flow n the lne ncludng the transacton to the magntude ofthe correspondng transacted power. It s gven as, Then (3) becomes, = P m n (4) P = =1 P (5) The change n real power flow due to multlateral transactons s, = ns =1 =1 P = t P (6) III.TRANSACTION COST ALLOCATION A. Wheelng Charges The suggested method evaluates the change n power flow n all transmsson lnes when a new transacton sntroduced n the system. Wheelng charges to the transacton are then allocated n proporton to the rato of tsabsolute value of actual faclty usage and the magntude of total power flows. The proposed allocaton rule due toblateral transacton s gven as follows, P WC t = C m n Alllnes P0 m n + P (7) Where WC t s wheelng charge for transacton t, 0 C m n s charge for transacton faclty m-n andp m n s base case real power flow.for multlateral transacton, total change n power flow due to all transacton can be obtaned by (6). Wheelng Charge for multlateral transacton can be wrtten as SWC t = 3 WC t andbwc t = 7 WC t Copyrght to IJIREEICE 80 (10) Also for multlateral transacton, the cost has to be allocated to ndvdual seller and buyer based on ther usage ofthe transmsson facltes. For ths, the usage of transmsson lne by ndvdual seller and buyer has to beseparated. The usage of lne m-n by the seller at bus due to multlateral transacton s calculated by (5),Smlarly, the usage of lne m-n by the buyer at bus due to multlateral transacton s gven by, ns = =1 P (11) The wheelng charge for seller for usng all the lnes SWC and the wheelng charge for buyer for usngall the lnes BWC are gven by, SWC t = r m n Alllnes BWC t = r m n Alllnes (1a) (1b) Where, r m n s the charge rate of lne m-n n $/MWhr whch s obtaned by dvdng the cost for each lne by total usage of that lne by all the transactons. r m n = C m n P0 m n + P (13) The proportonal sharng of the cost to seller and buyer for the case of 50% share to seller and 50% share tobuyer the cost s evaluated by followng equatons, SWC t = SWC t andbwc t = BWC t (14) Smlarly for 30%-70% sharng polcy the followng formulae are used,

3 ISSN (Onlne) ISSN (Prnt) SWC t = 3 SWC t andbwc t = 7 BWC t (15) IV.ALGORITHM Step1. Read system bus data and lne data. Step. Run base case power flow soluton. Step3. Consder blateral transacton between seller and buyer, or multlateral transacton between group ofsellers and buyers. Calculate TIF values usng (4). Step4. The change n power flow due to power contract s evaluated by (6). The value of ns and are equal to 1 forblateral transacton n (6). Step5. Cost of transmsson transactons for blateral transacton s calculated by (7). Step6. If multlateral transacton s consdered then fnd cost of transmsson transacton by (8). Step7. The transmsson usage cost allocated to seller SWC t and buyer BWC t for the use of all lnes s calculated byusng (9) or (10) for blateral transacton. Step8. If multlateral transacton s consdered then the transmsson usage cost allocated to seller SWC t and buyerbwc t for the use of all lnes s evaluated by usng (14) or (15). V. RESULTS AND DISCUSSION In ths paper, an analytcal method s proposed usng TIF for the calculaton of transmsson transacton cost andthe results are compared wth conventonal Megawatt Modulus (MM) method [8]. The proposed method s tested onsample sx bus system and IEEE 30 bus system. The program s developed n MATLAB 7.0 envronment. A. Sx bus system The sample sx bus system [10] conssts of three generators, three loads and eleven transmsson lnes. The totalsystem demand s 10 MW. The frst bus s consdered as slack bus. One blateral transacton T1 and a multlateraltransacton T wth two cases are consdered for ths system. (1) Blateral transacton (T1) of 0 MW between seller bus and buyer bus 5 TIF values are obtaned for the above transacton by (4). The TIF values for transacton T1 and change n powerflow due to ths transacton are gven n Table I. Once the transacton mpact factor for any transacton s known thent s easy to calculate the change n power flow due to that transacton by multplyng TIF wth the magntude ofpower transacted as gven n (6). The actual power flow after ncludng partcular transacton s obtaned by addng the change n power flow dueto that transacton wth the base case power flow. TABLE I. TIF VALUES AND CHANGE IN POWER FLOW FOR 6 BUS SYSTEM Lne m-n TIF values For the transacton T1, the actual power flow n all the lnes obtaned by proposed method s compared wth thenewton Raphson (NR) power flow soluton values and they are gven n Table II. Power flow n each lne obtaned byboth methods s almost same. In proposed method, no need to run the power flow soluton repeatedly. Theadvantage of the proposed method s best beng explaned wth the help of multlateral transacton n the followngsectons. TABLE II. POWER FLOW COMPARISON FOR T1 Lne Power flow m-n NR Proposed method method Change n Power flow The total wheelng charges for transacton T1 s obtaned by (7). The cost for each lne Cm-n s assumed as thevalue of lne reactance for that lne multpled by 1000 n $/hr. The total wheelng charge for T1 s $/hr. Thsamount s allocated among the seller and buyer by two cases of cost sharng polcy as per Table III based on (9) and(10). Also the results of proposed method are compared wth Megawatt Modulus (MM) method [8]. The MM methodneeds two power flow solutons, one s wthout transacton and the other s wth the transacton to fnd the changen power flow. wheelng charges obtaned by both the methods are almost smlar. TABLE III. COST ALLOCATION FOR T1 Copyrght to IJIREEICE 81

4 ISSN (Onlne) ISSN (Prnt) Cost for Cost for Sharng Seller at Buyer at cost Method polcy (%) bus bus Proposed MM Proposed MM () Multlateral transacton T - case 1 A Multlateral transacton T of case 1 s consdered for the sx bus system as per Table IV. The prefx S refersseller bus and B refers buyer bus. There are two seller buses 1, and two buyer buses 4, 5 nvolved n thstransacton. Buyer at bus 4 s agreed to buy 10 MW from seller 1 and 5 MW from seller to meet ts demand of 15MW. Smlarly Buyer at bus 5 s agreed to buy 5 MW from seller 1 and 10 MW from seller to meet ts demand of 15MW. of 30 MW s transacted n ths multlateral transacton. TABLE IV. MULTILATERAL TRANSACTION T - CASE 1 Transacton MW n Generaton To B4 ToB5 From S From S Load Ths multlateral transacton ncludes four transactons. The TIF for all these transactons are calculated and gvenn Table V. These factors are constant for any possble magntude power transacted between these sellers andbuyers. The TIF values may be postve or negatve dependng upon the power flow drecton. But n calculatngwheelng charges, the magntude of TIF s consdered. For any possble combnaton of power contracts the lne flowmpacts can be easly obtaned. The change n power flow for ths multlateral transacton s gven n Table VI. Herethere are two ns and two. Actual power flow n each lne by proposed method s calculated by summng up thschange n power flow wth the base case power flow. The total wheelng charge for multlateral transacton evaluatedby (8) s 96.8 $/hr. Ths cost s allocated among the sellers and buyers based on ther usage of the transmsson faclty to carry out ths transacton. The cost for two seller buses and two buyer buses are allocated by (14) and (15)and gven n Table VII TABLE V. TIF VALUES FOR T - SAMPLE 6 BUS SYSTEM Seller at bus 1 Seller at bus Lne m-n Buyer at Buyer at Buyer at Buyer at bus 4 bus 5 bus 4 bus TABLE VI. CHANGE IN POWER FLOW FOR T-CASE1 Seller at bus 1 Seller at bus Lne m-n Buyer at Buyer at Buyer at Buyer at bus 4 bus 5 bus 4 bus The cost for S and B5 are hgh because the usage of the transmsson network by these partes are more byprovdng more mpact n lne flows. The same pattern of results s obtaned n MM method also. But the MM methodneeds fve power flow solutons to evaluate the change n power flow for ths multlateral transacton. One for basecase and four for transacton cases wth specfed magntude. If any one of the transacton magntude changes thenpower flow soluton has to be done agan. TABLE VII. COST ALLOCATION FOR T - CASE 1 6 BUS SYSTEM SWCt($/ hr) 50 % - 50 % share 30 % -70 % share Proposed mm Proposed Mm $/h r) SWCt( $/h r) SWCt($/h r) $ /hr SWCt($/hr ) $/h r S S B B Whee lng charg e Copyrght to IJIREEICE 8

5 ISSN (Onlne) ISSN (Prnt) (3) Multlateral transacton T - case To explan the advantage of proposed method one more transacton case s consdered for the same multlateraltransacton between seller buses 1, and buyer buses 4, 5 wth dfferent power level as per Table VIII. Here total of 40 MW s transacted between the partes. Buyer at bus 4 s agreed to buy 10 MW from seller 1 and 10 MW fromseller to meet ts demand of 0MW. Smlarly Buyer at bus 5 s agreed to buy 15 MW from seller 1 and 5 MW fromseller to meet ts demand of 0 MW TABLE VIII. MULTILATERAL TRANSACTION T - CASE Transacton n MW Generaton To B4 To B5 From S From S Load For transacton case of T, snce the partes nvolved n the transacton remans same, the TIF factors are alsosame as n Table V. The change n power s obtaned by (6) s gven n Table IX. But n MM method, the power flowsoluton shouldbe repeated for every change n power transacted. The actual power flow obtaned n ths case alsosmlar to that of NR method. The total cost allocated for multlateral transacton of 40 MW s about $/hr. The transmsson usagecharges for dfferent percentage of sharng n transmsson cost for seller and buyer s evaluated and gven n Table X.In case of 50%-50% share to seller and buyer, the buyer wll get benefted and whereas n the case of 30% -70%share, the consumer pays maxmum share, so the seller wll get benefted. TABLE IX. CHANGE IN POWER FLOW FOR T- CASE Lne Seller at bus 1 Seller at bus m-n Buyer at Buyer at Buyer at Buyer at bus 4 bus 5 bus 4 bus TABLE X. COST ALLOCATION FOR T CASE 6 BUS SYSTEM B. IEEE 30 bus system The numercal data for IEEE 30 bus system s taken from [11]. In ths system there are 6 generators, 4 loads and41 transmsson lnes wth the total demand of 83.4 MW. Generator connected at bus 1 s consdered as slack. Amultlateral transacton wth two cases s consdered for ths system. (1) Multlateral transacton - case 1 Multlateral transacton nvolvng three seller buses,5,8 and three buyer buses 1,16,9 s consdered as gven n Table XI. of 50 MW s transacted n ths multlateral transacton. S8 has hghest generaton and B1 has hghest load n the transacton consdered. The TIF for all the nne transactons s calculated as explaned earler. TABLE XI. MULTILATERAL TRANSACTION CASE 1 FOR IEEE30 BUS SYSTEM Transacton n MW Copyrght to IJIREEICE 83 Generaton To B1 To B16 To B9 From S From S From S Load 50 % - 50 % share 30 % -70 % share Proposed mm Proposed Mm SWCt( SWCt The actual lne flows n all the lnes due to contract case 1, by proposed method and NR method are compared and multlateral transacton s wthn the lne capacty. The aboveconsdered multlateral transactons provde hghest mpact on flow n frst lne 1- (7.13 MW) because generatonat bus 1 ncludng base case s the maxmum of all. The lne number 9, 30 and 37 has least mpact of power flowbecause these lnes are relatvely away from the buses that nvolved n the consdered transacton. SWCt Fg. 1. Power flow by proposed method for transacton case 1 - IEEE 30 bus system. $/hr SWCt S S B B Wheelng charge $/hr

6 ISSN (Onlne) ISSN (Prnt) shown n Fg.1. For all the lnes the flow due to ths () Multlateral transacton - case In the multlateral transacton case, eght transactons are consdered as gven n Table XII. generaton n 8 th bus s the hghest of 30 MW, but n case 1 ts value s 3 MW. TABLE XII. MULTILATERAL TRANSACTION CASE FOR IEEE30 BUS SYSTEM Transacton n MW To Generaton B1 To B16 To B9 From S From S From S Load The actual lne flows n all the lnes due to above contract case, by proposed method and NR method arecompared n Fg.. These transactons provde hghest mpact on flow n lne number 1 connected between buses 1and (7.015 MW). The lne number 30 between buses 18 and 19 has least mpact (0.68 MW) because the buses18 and 19 are not nvolved n the transacton case consdered. The cost allocated n sharng polcy and sharng polcy for both the contract cases are compared nfg.3. In both cases of cost sharng, the total cost recovered for the use of transmsson network for transacton case-1 s $/hr. Smlarly for transacton case-, the total cost recovered for the use of transmsson network s464. $ /hr. The total wheelng charges n case ncreases because of the ncrease n total MW transacted n thscase. The cost obtaned by proposed method for these two transacton cases are almost smlar to the cost calculatedby MM method. VI. CONCLUSION The developed Transacton mpact factors relate the lne flows wth the magntude of power transacted betweenthe sellng and buyng enttes. The MM method to evaluate the transacton-related flows on all network lnes, needsthe repeated power flow soluton consderng the nodal power nectons only nvolved n that transacton. In theproposed method, once the TIFs are obtaned for a gven transacton, t does not requre one to perform the powerflow soluton to evaluate the transacton related power flows whenever any gven dfferent possble combnatons oftransactons are exercsed. Therefore, the proposed method s well suted for real tme applcaton. The manadvantage of the developed method les n ts capablty to consder multlateral transacton smultaneously. The costallocated to ndvdual seller and buyer and the varous schemes of cost sharng prncple between seller and buyer are also provded. Ths helps n takng correct economc decson. REFERENCES [1] D.Shrmohammad, Ch.Raagopalan, E.R.Alward and C.L.Thomas, Cost of transmsson transactons: anntroducton, IEEE Trans. on Power Syst., vol.6, no.3, pp , [] J.W.Marangon Lma, Allocaton of transmsson fxed charges: an overvew, IEEE Trans. on Power Syst., vol.11,no.3, pp , [3] J.Balek, Topologcal generaton and load dstrbuton factors for supplement charge allocaton n transmssonopen access, IEEE Trans. on Power Syst.,vol.1, no.3, pp , [4] D.krschen,D.Ahmed,G.Strbac, Allocatng Transmsson System Usage on the Bass of Traceable Contrbutons ofgenerators and Loads to Flows, IEEE Trans. on Power Syst.,vol.13, no., pp , [5] F.D.Galana,A.J.Coneo and H.A.Gl, Transmsson cost allocaton based on equvalent blateral exchanges, IEEETrans. on Power Syst., vol.18, no.3, pp , 003. [6] A.J.Coneo, J.Contreras, D.A.Lma, and A.Padlha-Feltrn, Zbus transmsson network cost allocaton, IEEE Trans. OnPower Syst., vol., no. 1, pp , 007. [7] K.L.Lo, M.Y.Hassan and S.Jovanovc, Assessment of MW-mle method for prcng transmsson servces: anegatve flow-sharng approach, IET Gener:, Transm. Dstrb., vol.1, no.6, pp , 007. [8] R.Kovacs and A.Leverett, A load flow based Method for Calculatng Embedded, Incremental and Margnal cost oftransmsson Capacty, IEEE Trans. on Power Syst., vol. 9, no. 1, pp. 7 78,1994. [9] J.Pan, Y.Teklu and K.Jun, Revew of usage-based transmsson cost allocaton methods under open access, IEEETrans. on Power Syst., vol.15, no.4, pp , 000. [10] A.J.Wood, B.F.Wolleerg, Power generaton, operaton and control, Wley, New York, [11] washngton.edu/research/pstca. Fg.. Power flow by proposed method for transacton case - IEEE 30 bus system BIOGRAPHIES N.NARENDRA REDDY s pursung Master of Technology n Electrcal Power Systems Engneerng from JNTUA College of Engneerng Pulvendula , Andhra Pradesh, Inda. He s presently workng on hs proect under the gudance of Asst.Professor K.Vmala Kumar. Copyrght to IJIREEICE 84

7 ISSN (Onlne) ISSN (Prnt) K.Vmala Kumar receved the Master of Technology degree n Electrcal & Electroncs Engneerng from Jawaharlal Nehru Technologcal Unversty Hyderabad, Inda 008. He s a research student of Jawaharlal Nehru Technologcal Unversty, Ananthapur, Inda. Currently he s workng as Assstant Professor n the department of Electrcal and Electroncs Engneerng, J.N.T.U.A College of Engneerng, Pulvendula , Andhra Pradesh, Inda. Hs nterest areas are power system deregulaton, power system peraton and control, power system desgn and dynamc load modellng. Copyrght to IJIREEICE 85