COST OF TRANSMISSION TRANSACTIONS: Comparison and Discussion of Used Methods

Transcription

1 INTERNATIONAL CONFERENCE ON RENEWABLE ENERGY AND POWER QUALITY (ICREPQ 03) COST OF TRANSMISSION TRANSACTIONS: Comparion and Dicuion of Ued Method Judite Ferreira 1, Zita Vale 2, A. Almeida Vale 3 and Ricardo Puga 4 1,2,4 Polytechnic Intitute of Porto (IPP)/Intitute of Engineering (ISEP)/Department of Electrical Engineering (DEE) Rua Dr. António Bernardino de Almeida Porto- Portugal phone: , fax: , mjudite@dee.iep.ipp.pt, zav@dee.iep.ipp.pt, 3 Univerity of Porto (UP)/Scholl of Engineering (FEUP)/Department of Electrical Engineering and Computer (DEEC) phone: fax: aav@fe.up.pt Abtract Power maret deregulation impoed the eparation of everal activitie uch a power production, tranmiion and ditribution, with the conequent eparation of thee activitie cot. Thi article preent and compare method that allow determining how much and who mut pay for the ue of the electrical tranmiion networ. Thi iue i analyed, under the point of view of everal tranmiion ytem uer: generator, load and tranaction being analyed. The advantage and diadvantage of each method, from the point of view of the conidered uer are dicued. The embedded method are ued a the bae of cot calculation, pecifically the method Potage-Stamp and MW-mile and ome of it variant. Thi tudy i illutrated uing a imple nine-bu electrical networ that being ued by R&D group for everal project concerning power maret. Keyword Power tranmiion economic, Power tranmiion line, Wheeling tranaction, Tranmiion pricing, Embedded methodology. 1. Introduction In the competitive electric energy maret it i important to quantify efficiently the cot aociated to each activity in the ector [1,2]. The main cot aociated to the maret of electric energy are the cot of production, cot of tranmiion and cot of ditribution. Thi paper tudie and calculate the tranmiion cot, aociated to a wheeling tranaction. The tudy cae preent a et of twenty tranaction that correpond to bilateral contract between generator and load. The electric networ ued in thi tudy i repreented in the Fig. 1. Fig. 1: Example Networ For calculation of the taxe to be impute to each R( tranaction the embedded methodology wa ued. The development tool ued are: Matlab for implementation of the embedded method and the Power World imulator to carry out the imulation of Power Flow. 2. Theoretical Development In the embedded method all ytem cot, exiting tranmiion ytem, operating and expanion, thee cot are allocated among ytem uer in proportion to their extent of ue of the tranmiion reource. Allocation methodologie differ on their definition and meaure of thi extent of ue. They can be claified a load flow baed method and rolled-in method uch MW-mile and Potage-Stamp methodology repectively [3]. The main value difference between the Potage-Stamp and MW-mile method i that: the MW-mile ue the calculated value of power flow in it implementation, while the Potage-Stamp method doe not ue thi calculation. The tudied method are: Method of Rolled type in Potage-Stamp, MW-mile RE&PQJ, Vol. 1, No.1, April 2003

2 (claic), Bae, Module or Ue, Zero Counterflow and Dominant Flow. To the long one of the related analyi, the variable and expreion are ued to follow preented: - Circuit that bind bu i with bu j C - Cot of line, (Euro) - Line capacity (MW) F - Flow in line in the initial condition (MW) L - Length of the line (m) CT = C - Total cot of tranmiion (Euro) F ( - Impact of tranaction u in line (MW) W ( - Power of tranaction u (MW) R ( - Allocated cot to agent u (Euro) PG (g) - Power produced for the generator g A - Method of Rolled type in Potage-Stamp Thi method i of imple implementation. It calculation i baed on the amplitude of the power tranaction. The meaure of thi amplitude normally i gotten at the moment where the ytem reache maximum power. Being the tariff, repreented by P, the ame for all the tranaction and R( the tax to aign to each tranaction u proportional to P. The expreion 2 allow the calculating of R( [3]. P = g CT PG( g) (1) R = P W (2) Thi method preent ome diadvantage: it doe not conider the actual tate of the ytem o it becaue of thi doe not give true economic information to the uer. Doe not induce a load increae in the zone where exit bigger production, neither the intallation of new generator in area with bigger conumption. For example independent generator do have not incentive. With thi method a tranaction in which the load and the generator are cloe, what mean uing lightly the ytem, may have to ubidize other tranaction that ue much more the ytem. Moreover, thi method doe not conider the networ and the power flow involved. The methodologie alo preented in ection B, C, D, E, F, are baed on the calculation of power flow with intention to conider the tate of the networ. B - MW-Mile (claic) Thi methodology i of imple implementation. It conider the contribution of each tranaction to the power flow in the line and the amount ued of networ for each tranaction. The expreion (4) how how to determine the tax to be paid for the R( tranaction [3]. CT P = (3) F L R = P F L (4) However, thi method ha ome diadvantage. In fact, it i only applicable to bilateral tranaction where the point of injection and reception are nown. For that reaon it ue i impracticable in a Pool. Thi method conider that all the negative flow aociated to a tranaction are beneficial to the networ. However, thi only ha real mean in the cae of the line near the limit. Another inconvenience of thi method i that it doe not have an economic bai. Therefore it doe not tranmit adequate economic ignal to the uer, for example indicating i the availability of the equipment. The method preented in next ection reduce the diadvantage of the MW-mile (claic). C Bae There i a great difference between thi method and the original MW-mile [4]. While the original method conider the maximum capacity of the line in denominator, thi method ue the total flow of the line. With thi method the total cot of the ytem i ditributed by all the tranaction, according to the expreion (5) that allow to calculate R(. R F = C (5) F ( ) With thi method, ome of the R( taxe can be negative, what it mean that one definitive tranaction can receive a credit to ue the tranmiion ytem. Thi i alway verified when active power flow provoed by thi tranaction i in contrary direction to the one of the active power flow in the initial condition of the ytem. Effectively, thi fact alone i important in the cae of the line wor near to it capacity, in cae that if it doe not verify, ome of the uer of the networ pay ufficiently, in benefit of that receive but that in the reality they had not brought benefit ome for the operation of the ytem. D - Module or Ue Thi method ditribute the total cot of the ytem for the different tranaction, conidering tranaction in both direction. In thi way, all pay, but the cot i more ditributed, becoming cheaper for the cae where the tranaction doe not reduce the flow in the line. The expreion (6) how how to determine the tax to be paid for the R( tranaction [3] RE&PQJ, Vol. 1, No.1, April 2003

3 F R (6) F ( ) = C The difference of thi method in relation to the MW-mile (Bae) i that it conider the abolute value of the line flow originated by tranaction u, intead of hi igned value. E - Zero Counterflow The Zero Counterflow method only taxe the poitive flow. Thi method aume that the negative flow are beneficial for the networ, therefore in thee cae the tranaction are not paid but alo they do not have credit. The expreion (7) how how to determine the tax to be paid for the R( tranaction [3]. R( = 0 C F FD ( ) for F > 0 for F 0 (7) F if F > 0 FD = (8) 0 if F 0 The function FD ( only conider the impact, provoed for the tranaction u in line, when thee increae the active power flow in thi line. F - Dominant Flow Thi method i the join of the two previou method. It i conidered that R( i the addition of two parcel RA( and RB(. The parcel RA( i determined uing the Zero Counterflow method ubtituting cot C for CA. The parcel RB( i determined uing the Modulo or Ue method where C i ubtituted by CB. Factor CA correpond to the cot due to the tranit in the line for the bae cae of the ytem and CB correpond to the cot of the not ued capacity. The expreion (9) how how to determine the tax to be paid for the R( tranaction [3]. R = RA( + RB( (9) CA RA( = 0 RB( = CB CA CB = C = C F FD ( ) F F F ( ) F For F > 0 For F 0 (10) (11) With thi method all the participant that ue the ytem in the oppoite direction of the reultant flow receive an incentive, which conit of leer cot. Thi incentive increae when the ytem i more loaded, arriving to zero cot when the ytem i to the maximum load. Thee economical ign are coherent with the intent of reducing expanion cot. 3. Study Cae For thi tudy cae are calculated the imputed taxe for the 20 tranaction that are preented in the cenario preented in table I and table II. Thee tranaction are relative to the bilateral contract carried through between generator and load that integrate the networ preented in figure 1. In thi tudy cae all the produced power i commercialied by bilateral contract for the period of one year. It i conidered the pair generation/load, a are repectively the production and it aociated load to one determined wheeling agent, or traditional utility. Table I: Scenario of Tranaction (MW) Load L1 L2 L3 L51 L52 Ger (MW) G T G2 350 T G T G T5-100 T7-160 G T G T G T8-40 G Where: RE&PQJ, Vol. 1, No.1, April 2003

4 Table II: Scenario of Tranaction (continuation) Load L6 L7 L8 L9 Ger (MW) G G2 350 T9-30 T12-20 T T G T G T G T T19-15 G G8 200 T T16-50 T20-10 G T Reult After the accomplihment of all the imulation that had allowed calculating the taxe to impute to the 20 tranaction had been gotten the reult preented in table VIII of the appendix A. With thee reult comparion are carried through that allow getting ome concluion preented in ection 5. The total cot of tranmiion i Euro (CT). It i calculated appealing of attributed cot C to each line (value preented in table VII of the appendix A), according to following expreion: The imulator ued to obtain the power flow in the tranmiion line wa the Power World Simulator. Firt, wa been determinate the power flow at the bae tate of the ytem, preented on F, with all the load and generator connected in the networ and with not reitance line conideration. To calculate the contribution due to each tranaction u (pair generator/load), i removed the pair aociated to it and in thi ituation the power flow i carried out with a new imulation. Analying the reult of thee two imulation allow to calculate the power flow in the F ( line, aociate to the tranaction u. Thi proce i repeated for all the tranaction. Uing the embedded method, and nowing the contribution of each tranaction in each line, i calculated R( the tax to aign to each tranaction u. The Matlab wa the programming tool ued to the implementation of the expoed method. The oftware architecture i preented in Fig. 2. = CT (12) C all line CT = C C C C C C C C C C C C C 8-9 CT = Euro. The Taxe imputed to each tranaction are preented in the table VIII of the appendix A. With thee value, it i poible to compare the imputed cot to ome of the intervening one in the tudied cenario. Thee cot are compared to the tranaction, generator and load that preent imilar characteritic, uch a: tranaction, generator value and load with imilar value. A - Compare Taxe Imputed to the Tranaction Tranaction of 100 MW The tranaction T1 and T15 have the ame tranaction power (100MW), however are taxed with different value a preented in the graph of Fig. 3 and in the table III. Fig. 3: Taxe Imputed to the Tranaction T1 and T15 Fig. 2: Software Architecture The two tranaction pay different value, becaue the ditance from load to generator, that correpond to each one of the tranaction alo are different. The fact of the value taxed to T15 i bigger than the other tranaction i due to the fact of thee ue more the networ and i more remote from the production contract point RE&PQJ, Vol. 1, No.1, April 2003

5 Table III: Taxe Imputed to the Tranaction T1 and T15 T1 T15 Potage-Stamp MW-mile (Claic) Bae Module or Ue Zerocounterflow Dominante Flow Tranaction of 50 MW Conidering the T2 and T16 tranaction, worthy lie 50 MW, the value to impute are preented in the table IV and repreented graphically in the figure 4. The difference of the value of the taxe imputed to the tranaction T2 and T16, that have the ame contractual value of power, it i becaue the contract between the load L2 and the generator G1 (that give origin to the T2 tranaction) are not connected in the ame bu. B - Compare Taxe Imputed to the Generator Analying from the point of view of the generator, for example generator producing 200 MW, the tax to impute i repreented in the graphic of the Fig. 5 and table V. In thi analyi it i verified that the method where the taxed value are more identical are the Module or Ue, Zero Counterflow and Dominant Flow. Although thi method don t give credit to the generator but they tax them with le value. For example the generator G8 in thee lat three method doe not receive, but i what pay le. With thi analyi wa concluded that the generator that inject the ame power could be taxed with different value. Thee value depend on with and who the producer have it contract, and which the effect of thee contract in the active power flow. Fig. 4: Taxe Imputed to the Tranaction T2 and T16 The T16 tranaction i taxed in almot all the method with practically null value, compared with the total cot of tranmiion. The exception i the Pot Stamp method where the tranaction i taxed in 3,14 % (2066 Euro). Thi happen becaue the load L8 and the generator G8 are located in the ame bu and they are the implicated in the tranaction T16. Table IV: Taxe Imputed to the Tranaction T2 and T16 T2 T16 Potage-Stamp MW-mile (Claic) Bae Module or Ue Zerocounterflow Dominante Flow The value in the table IV, for the taxe imputed to the tranaction T16, are not exactly zero, what i jutified due to the rounding of the calculation. By the analyi of the graph repreented in figure 4, it i verified that T2 i taxed with poitive value in the method Pot-Stamp, Bae, Module or Ue, Zero Counterflow and Dominant Flow and with negative value for the method MW-mile Claic. Fig. 5: Taxe Imputed to the Generator G3 and G8 Analying the graphic of Fig. 4, we can conclude that G3 regarding the G8 pay alway the ame or more, being G8 be able to receive. Thi happen, when the method MW-mile claic and Bae are ued. Table V: Taxe Imputed to the Generator G3 and G8 G3 G8 Potage-Stamp MW-mile (Claic) Bae Module or Ue Zerocounterflow Dominante Flow The generator G8 ha greater number of tranaction regarding the G3, for the ame total power tranacted. Therefore, we can conclude, that may be more advantageou to the generator mae everal tranaction, when the networ i ued RE&PQJ, Vol. 1, No.1, April 2003

6 C - Compare Taxe Imputed to the Load The aim of the comparion, of the taxe imputed to the load, i verify which the approach are more economical advantageou, if the utilization of the tranmiion networ i pay by conumer. The value preented in table VIII, are gotten adding the taxe imputed to all the tranaction aociated with the contract mae for one load. For example, the value to tax to the load L5_1, wa gotten adding the taxed value of the tranaction T5 and T6 that are aociate to the load L5_1. The value of thee taxe are preented in table VI and figure 6. Compare Taxe Imputed to the Load L1 and L5_1 The load L1 and L5_1 have lightly different value of active power, thi i the load L5_1 ha a value of active power 10% greater that the L1 load. Thee load have the following act of contract: - The L1 load contract 100 MW to the G2 generator. - The L5_1 load contract to the generator G4_1 the power of 100 MW and 10 MW to the G4_2. Thi contract are carried through in two cae between conecutive bue, however the line length that connect bu 1 to bu 2 are of 405 m and the ditance between bu 4 and bu 5 are of 578 m, what mean that the L5_1 load i about 173 m more ditant from the power injection point than the L1 load. Table VI: Taxe Imputed to the Load L1 and L5_1 L1 L1+10%L1 L5_1 Potage-Stamp MW-mile (Claic) Bae Module or Ue Zerocounterflow Dominante Flow The taxe imputed to the L1 load vary between, a value where the load receive 4966 Euro (7,56% abolute value), calculated by the method Bae and 6405 a maximum value to pay of Euro (9,75% of the total cot) taxed by the Claic MW-milha method. In the cae of the L5_1 load the boundary-value are of a minimum to pay of 3396 Euro (5,17%) calculated by the method Module or Ue and a maximum of Euro (31,27%) to pay calculated by the method Bae. It i alo verified that the taxe calculated by the method Potage-Stamp had increaed proportionally, with the increae of the value of the power contracted for the load. For the remaining method the value taxed to L5_1 increae more than 10% of the value taxed to L1, a can be analyed in table VI. For the comment of the graph of figure 6 it i a fact, that the price to pay for the load to the conceionaire of the networ i very variable, being the three lat method Module or Ue, Zero Counterflow and Dominant Flow, the mot advantageou for the load, although the load haven t the poibility to receive, uch happen in the method MW-mile claic in the cae of the load L1. 5. Concluion All the taxe calculated for the method preented in thi wor pay the total cot of tranmiion, a it can be verify in table VIII of the appendix A. Fig. 6: Taxe Imputed to the Load L1 and L5_1 Analying the value in the table VI and oberving the graph of figure 6, it i verified that for all the ix tudied method the load L5_1 pay alway more than the L 1 load. The value of the taxe that are in the column identified for (L1+10%L1), correpond to a auxiliary calculation that determine the value of the taxe imputed to L1 increaed in 10%. The method Potage-Stamp taxe all the tranaction in function of the contracted power value and the total tranmiion cot. What it implie for one electrical ytem, that all the tranaction with the ame value of power pay the ame for the ue of the tranmiion networ, jut that they do not ue it. For example, a tranaction between producer and conumer on the ame bu, that don t need ue the electrical line for the phyical concretiation of the tranaction, i taxed in the ame way that another one, that carrie through between producer and conumer who are in different bu, needing therefore to ue the networ. In relation to the method Bae, we conclude that thi method allow that the tranaction receive for the ue of the networ, although when they are taxed poitively pay very high value. We can be conclude that thi method in t advantageou to the tranaction, becaue it provoe great difference in the value taxed to the tranaction with equal power tranacted RE&PQJ, Vol. 1, No.1, April 2003

7 The taxe calculated for the method MW-mile claic preent the ame tendency that the value taxed by the method Bae, however with leer amplitude of the taxed value. For the method, Module or Ue, Zero Counterflow and the Dominant Flow, we conclude that they alway tax the tranaction with a poitive value. Although thi value are maller and more uniform, comparing identical tranaction. Thee taxe in certain ituation give ome incentive, but they do not provoe therefore a great increae of taxe for the tranaction where thi benefit if doe not verify. The method, MW-mile claic, Bae, Module or Ue, Zero Counterflow and the Dominant Flow, tax in function of the impact in the active power flow or in function of the ditance from the load point and the injection point. Thi reult in a null value for the taxe in the cae where the load and the generator are in the ame bu and the power injected for the generator i equal or uperior to the one of load. Appendix A Table VII: Electrical Characteritic Line Line R X C L Lim C (p.u.) (p.u.) (p.u.) (Km) (MW) (Euro/yr) 1_2 0,070 0,200 0, _7 0,050 0,200 0, _3 0,080 0,300 0, _7 0,050 0,250 0, _4 0,050 0,100 0, _5 0,060 0,300 0, _5 0,030 0,200 0, _6 0,120 0,260 0, _9 0,020 0,100 0, _7 0,200 0,400 0, _9 0,100 0,300 0, _8 0,020 0,100 0, _9 0,050 0,200 0, Reference [1] Iabel Praça, Carlo Ramo, Zita Vale, Manuel Cordeiro, A Multi-Agent Simulation Prototype Deciion Support in Electricity Maret, 2002 AI, Simulation and Planning in High Autonomy Sytem, Libon Portugal, pp , April [2] Iabel Praça, Carlo Ramo, Zita Vale, Manuel Cordeiro, A Multi-Negotiation Period Prototype for Competitive Electricity Maret Simulation, International Conference on Fuzzy Sytem and Soft Computational Intelligence in management and Indutrial Engineering, Itambul, Turquia, pp , May [3] D Shirmohammadi, C Rajagopalan, E R Alward, C L Thoma, COST OF TRANSMISSION TRANSACTIONS: AN INTRODUCTION, Tranaction on Power Sytem, vol. 6, Nº. 4, November [4] D Shirmohammadi, X V Filho and B Gorentin, M V P Pereira, SO ME FUNDAMENTAL TECHINICAL CONCEPTS ABOUT COST BASED TRASMISSION PRICE IEEE Tranaction on Power Sytem, vol. 11, Nº. 2, November Table VIII: Taxe Imputed to the Tranaction T Pot Cla Bae Mod Count Domin CT RE&PQJ, Vol. 1, No.1, April 2003