TRANSMISSION COST ALLOCATION SCHEMES CONSIDERING SECURITY UNDER DEREGULATED POWER SYSTEM

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1 IJEEE, Volume 2, Issue 5 (October, 2015) e-issn: p-issn: TRANSMISSION COST ALLOCATION SCHEMES CONSIDERING SECURITY UNDER DEREGULATED POWER SYSTEM 1 Ch.Vani, 2 J.Krishna Kishore 1,2 Deptt. Of Electrical And Electronics Engineering, QIS College Of Engineering & Technology, Ongole, A.P, India 1 vanichunduri@gmail.com, 2 kishorejampani@gmail.com Abstract- In deregulated electricity markets, cost allocation of transmission services is critical for transmission open access. It is necessary to develop an appropriate pricing scheme that can provide the useful economic information to market participants, such as generation, transmission companies and customers. Though many methods have already been proposed, but accurately estimating and allocating the transmission cost in the transmission pricing scheme is still a challenging task.the cost of the transmission network can be interpreted as the cost of operation, maintenance and construction of the transmission system. In this work three methods using AC power flow have been attempted. They are MW-Mile Method, MVA-Mile Method and GGDF method. The three proposed pricing methods are appiled to the IEEE 14-bus system and the results are compared to each other. These methods are done using programming in MATLAB. Load flow solution is observed by using Power world simulator software. Index Terms- Deregulated electricity market, AC power flow, MW-mile method, MVA-mile method, GGDF method. I.INTRODUCTION Fair pricing of the transmission service is one of the challenging issues that has to be faced after the deregulation of power systems. Objective measures are needed that will allow the transparent remuneration of transmission-network usage and that will give appropriate economic signals to the network users. To solve this problem, several approaches have been proposed. The postage-stamp method is a straightforward method because a tariff provides the transmission-network usage remuneration independently of the distance or location of the contractual power source and the drain throughout the entire power system. However, the time of a particular transaction and the increased transmission losses due to the transaction are not taken into account. The postagestamp method allocates the transmission costs among the various users of the transmission service only according to the amount of power involved in each transaction. It is commonly used for recovery of transmission investment under a regulated regime. Since this method ignores the actual system operation, it does not send the correct economic signal to the network users. The contract-path method artificially selects a specific path between a producer and a consumer according to the wheeling transaction, without performing a power-flow calculation. As a result, some transmission facilities that are involved in the actual energy transaction are ignored, thus their usage is not being paid. Given a transaction with the actual points of generation and load, the distance relating the transmission pricing method known as the MW-mile method [6] calculates the maximum transaction related power flow on every transmission line using dc power-flow and linear programming algorithms. The line length and a factor reflecting the cost per unit capacity of aline further multiply this value. The price is proportional to the transmission usage for the transaction. It does not, however, reflect the actual power flows and may, in certain cases, discourage competition. Another approach for power wheeling pricing, called MVA-Km method applying AC power flow, has also been developed. This approach is more reasonable and valid than the commonly used MW-mile method [6] which is based on DC power flow. Since the already developed transmission service pricing methods have certain difficulties in assessing the actual transmission network usage, this paper GGDF method was introduced, using this method contingency analysis, safe operation are determined. GGDF is the best way of transmission pricing among three Pricing methods. The paper is organized as follows: Transmission pricing methods are described in section 2. Algorithm and flow chart of MW-mile Method is described in section 3. Algorithm and flow chart of MVA-mile method is described in section 4. Algorithm and flow chart of GGDF method is described in section 5. The results and discussion are discussed in section 6. Finally, brief conclusions are described in section 7. II. TRANSMISSION PRICING METHODS The objective of any transmission pricing method is to allocate all or part of the existing and the new cost of transmission system to customers. However, tariffs for International Journal of Electrical & Electronics Engineering 9

2 transmission services are more often set by government regulations, and are based on its policy directives. The pricing of transmission services should be carried out to achieve the following goals are It recovers the capital and operating costs, It encourages efficiency of use and investment, It provides equal opportunity to all users, It offers a simple and understandable price structure, It is easily implementable. In general, the following three pricing schemes are employed for transmission services: Rolled-in (embedded) transmission pricing Marginal transmission Pricing Composite transmission pricing The transmission costs may include: Running costs, such as costs for operation, maintenance, and ancillary services. Past capital investment. Ongoing investments for Future expansion In the following, we discuss major transmission cost allocation methods. Some of these methods are used widely by electric utilities, while others are still in developmental stages 1. Postage-Stamp Rate Method 2. Contract Path Method 3. MW-Mile Method 4. Unused Transmission Capacity Method 5. MVA-Mile Method 6. Counter-flow Method 7. Distribution Factors Method 8. AC Power Flow Methods 9. Tracing Methods III.ALGORITHM AND FLOWCHARTOF MW- MILE METHOD Algorithm of MW-mile method: Step1: Run the load flow by using N-R method for base case data. Step2: compute the power flows of each line. Step3: Read the line lengths in miles. Step4: Fix the unit rate i.e.,$/mw/mile Step5: compute the transmission charges of each line by multiplying the power flows with unit rate and line lengths. Step6: Evaluate total cost of each generator. Step7: Evaluate the transaction cost for each generator. Transaction cost $ total transmission cost of each generator total transmission cost of all generators total line cost Step8: Calculate cost ($/MW) for each generator [3]. per unit cost $ MW each transaction cost power generation of generator TC t TC t T k K C k L k MW t,k k K C k L k MW t,k TC t cost allocated to transaction t TC total cost of all lines in $ L k length of line k in mile C k cost per MW per unit length of line k MW k flow in line k, due to transaction t T set of transactions K set of lines Flow chart of MW-mile method as shown in figure 1 Merits of MW-Mile Method: 1. It is insensitive to the order of wheeling transactions. This is because every transaction is treated separately by considering only those generators and loads that are associated with that transaction. Hence, there will be no dispute about the order in which the transactions should be considered. 2. It gives a correct signal to both short distance and long distance entities, unlike in postage stamp case. 3. The method is intuitively logical and conceptually straightforward. Demerits of MW-Mile Method are Since the method uses DC approximation of the power system, it leads to inaccuracy in calculating the extent of use of the network by a particular transaction. This is because the real power system is modeled by a set of non-linear equations. IV.ALGORITHMAND FLOWCHART OF MVA- MILE METHOD Algorithm of MVA-mile method: Step1: Run the AC load flow i.e., Newton -Raphson load flow for base case data. Step2: Evaluate the line flows of each line and slack bus power in the given power system. Step3: Read the line lengths in miles of the system. Step4: Fix the unit rate i.e.,$/mva/mile Step5: Evaluate the transmission charges of each line by multiplying the line flows with unit rate and line lengths. Step6: Evaluate total cost of each generator. Step7: Evaluate the transaction cost for each generator. Transaction cost $ total transmission cost of each generator total transmission cost of all generators total line cost Step8: Calculate cost ($/MVA) for each generator [3]. per unit cost $ MVA each transaction cost power generation of generator TC t TC t T k K C k L k MVA t,k k K C k L k MVA t,k TC t cost allocated to transaction t TC total cost of all lines in $ L k length of line k in mile C k cost per MW per unit length of line k MVA k apparent power flow in line k, due to transaction t T set of transactions K set of lines International Journal of Electrical & Electronics Engineering 10

3 Start Read bus data and Line data Compute Y bus Run the load flow by using N-R method for base case data. Evaluate the line flows of each line Read the line lengths in miles of the system. Fix the unit rate i.e.,$/mw/mile End No Check whether bus connected to generator or not? Yes Evaluate the transmission charges of each line by multiplying the line flows with unit rate and line lengths. Evaluate total cost of each generator Evaluate the transaction cost for each generator. Calculate cost ($/MW) for each generator. Figure 1.Flow chart of MW-Mile method Flow chart of MVA-mile method as shown in figure 2 Start Read bus data and Line data Compute Y bus Run the load flow by using N-R method for base case data. International Journal of Electrical & Electronics Engineering 11

4 Evaluate the line flows of each line Read the line lengths in miles of the system. Fix the unit rate i.e.,$/mva/mile End No Check whether bus connected to generator or not? Yes Evaluate the transmission charges of each line by multiplying the line flows with unit rate and line lengths. Evaluate total cost of each generator Evaluate the transaction cost for each generator. Calculate cost ($/MVA) for each generator. Figure 2.Flow chart of MVA-Mile method The MVA-mile method is an extended version of the MW-mile method. The extension is proposed to include charges for reactive power flow in addition to charges for real power flow. It has been shown that monitoring both real and reactive power, given the line MVA loading limits and the allocation of reactive power support from generators and transmission facilities, is a better approach to measuring the use of transmission resources. V. ALGORITHM AND FLOWCHART OF GGDF METHOD Algorithm of GGDF method: Step1: Run the load flow by using N-R method for base case data. Step2: compute power flows of each line Step3: Read the line lengths in miles Step4: Fix the unit rate i.e.,$/mw/mile Step5: Calculate A factors by using equation (10). Step6: Calculate D factors using A factors and using equation (12). Step7: Evaluate the tracing of line flow of each line by using equation (11). Step8: Evaluate total cost of each generator. Step9: Evaluate the transaction cost for each generator. Transaction cost $ total transmission cost of each generator total transmission cost of all generators total line cost Step10: Calculate cost ($/MW) for each generator [3]. per unit cost $ MW each transaction cost power generation of generator Generation Shift Distribution Factors (GSDFs or A factors): GSDFs or A factors provide line flow changes due to a change in generation. These factors can be used in determining maximum transaction flows for bounded generation and load injections. GSDFs or A factors are defined as[2] P l,jk A jk,i. P gi --- (1) P ge + P gi 0, jk R, i N e---- (2) P l,jk - Change in active power through the element jk in network. A jk,i - Generation shift factors through network element jk, corresponding to the change at bus i. P ge - Change in generation at slack bus. P gi - change in generation at bus i i e. GSD s (A factors) determined by DC power flow P B. δ ---- (3) P Vector of injected power in system buses δ vector of nodal voltage angles B- Nodal Susceptance matrix. Voltage angle results δ B 1. P ---- (4) International Journal of Electrical & Electronics Engineering 12

5 Which means (nothing with b 1 ji j N, i N the elements of B 1 ) 1 δ j i N b ji P i, j N ---- (5) Hence the relation (3) becomes P l B l. δ l ----(6) P l -Vector of power through elements of the network B l -Diagonal matrix of longitudinal susceptances of network elements jk. δ l -vector of difference of voltage angles from ends of network elements jk Writing in extended the relation (6) lead to: P l.jk B l,jk. δ j δ k, jk R ----(7) Using the relation (5), relation (7) becomes P l,jk B l,jk (b 1 ji P i ) (b 1 ki P i ) i N B l,jk. b 1 1 i N ji b ki. P i, jk R --(8) Equation (8) is linear and the modification of power through network element, P l.jk due to changing of power injected in bus i, P i can be expressed as P l,jk B l,jk b 1 1 ji b ki. P i -----(9) By comparing the equations (9) and (1), the expression of A factors for network element jk, corresponding changing of generated power in bus i A jk,i B l,jk b 1 1 ji b ki, jk R, i N e ---(10) i N Generalized Generation Distribution Factors (GGDFs or D factors): They determine the impact of each generator on active power flows thus they can be negative as well. Since GGDFs are based on the dc model, they can only be used for active power flows. GGDFs or D factors are defined as[2] P l,jk (D jk,i i N. P gi ), jk R----(11) P l,jk -Active power flow P gi -power generated in bus i D jk,i D factor of a network elements jk, corresponding to power generated in bus i D jk,i D jk,e + A jk,i P jk 0 (Ajk,i.P gi ) i N e + i N P gi A jk,i ----(12) 0 P jk - Power flow on network elements jk from the previous iteration. e- Slack bus. It determines the impact of each generator on active power flow on network elements (they can have negative values). D factors reflect the utilization rate of electricity transmission capacity depends upon the generated power and they depend on network elements and operating regime and not on the choice of reference bus. Flow chart of GGDF method as shown in figure 3. Start Read bus data and Line data Compute Y bus Run the load flow by using N-R method for base case data. Evaluate the line flows of each line Read the line lengths in miles of the system. Fix the unit rate i.e.,$/mw/mile Compute A factors of all buses End No Check whether bus connected to generator or not? International Journal of Electrical & Electronics Engineering 13

6 Yes Compute D factors of Generator connected buses NO Check whether bus connected to generator or not? Yes Evaluate the tracing of line flow of each line Evaluate the transmission charges of each line by multiplying the tracing line flows Evaluate total cost of each generator Evaluate the transaction cost for each generator. Calculate cost ($/MW) for each generator. VI. RESULTS AND DISCUSSION This system consistsof14buses, 20linesections, 2generator buses and 11 load buses.figure 4 shows the line diagram for the IEEE14-bus system. Bus 1 is assumed to be reference bus. results of line flow shown in Table1.The results of MW-Mile,MVA-Mile, and GGDF methods as shown in tables 2,3 and6. Table 4 represents the D factors of 14-bus system and Table5 represents transmission usage allocation using GGDFs. These results are obtained based on the algorithm steps. When comparing all the results GGDF method is the best way of transmission pricing, among all embedded cost based methods. Figure 5 represents load flow results by using power world simulator. Figure 3.Flow chart of Distribution factor method Figure 4.IEEE-14 BUS SYSTEM International Journal of Electrical & Electronics Engineering 14

7 Figure 5.Power flow result of IEEE 14 bus system Line i j P ij Q ij MVA ij P loss Q loss Table 1: Line flow results of 14 bus system International Journal of Electrical & Electronics Engineering 15

8 Line i-j C k L k MW 1,k C k L k MW 2,k Total C k L k MW t,k t T k K TC t Cost($/MW) Table 2: Allocation of transmission pricing using MWmile method for IEEE-14 bus system Line i-j C k L k MW 1,k C k L k MW 2,k Total C k L k MW t,k t T k K TC t Cost($/MW) Table3: Allocation of transmission pricing using MVAmile method for IEEE-14 bus system Line i-j D ij,1 D ij, Table 4: D factors of IEEE-14 bus system International Journal of Electrical & Electronics Engineering 16

9 i-j G1 P ij G2 P ij avg P ij Table5: IEEE-14 bus system Transmission Usage Allocation using GGDFs Line i-j C k L k MW 1,k C k L k MW 2,k Total C k L k MW t,k t T k K TC t Cost($/MW) Figure 6. IEEE-14 bus system Transmission cost G1 of each line Figure 7. IEEE-14bus system Transmission cost G2 of each line Figure 8. IEEE-14 bus system total transmission cost comparison Table 6: IEEE-14 bus system Transmission cost allocation for GGDF method The plots which represents the comparison of Transmission cost of each generator, total transmission cost and cost ($/MW) of three methods were shown in figures6,7,8 and 9. Figure 9. IEEE-14 bus system Cost ($/MW) of each generator International Journal of Electrical & Electronics Engineering 17

10 VII. CONCULSION One of the main objectives in electric industry s restructuring is to bring fairness and open access to the transmission network. For IEEE-14 bus system the cost comparison figures 6,7,8 and 9 shows that overall transmission cost of the system is less in GGDF method compared to MW and MVA-mile methods but per unit MW cost is less in MW and MVA -mile methods. GGDF is the best way of transmission pricing among all Pricing methods. However, these pricing methods are able to full fill transmission pricing objectives: economic efficiency, non-discrimination, transparency and cost coverage and can be also applied to large power systems. It overcomes the limitation of postage stamp and contract path methods. As transmission system has become a separate entity. The purpose of the present work is to allocate the cost pertaining to the transmission lines of the network to all the generators and demands. With these methods correct economic signals are generated for all players. ACKNOWLEDGEMENT The authors would like to thank QIS COLLEGE OF ENGNEERING AND TECHNOLOGY, Ongole for providing the computer lab facility with necessary software. REFERENCES [1] A.R. Abhyankar and S.A. Khaparde, Introduction to Deregulation in Power Industry, IIT, Mumbai,pp.1-28 [2] Ravitheja Vambala, Prof.Dr. M. Padmalalitha, K.V.Kishore, P. Udai Kumar. Transmission Cost Allocation Using Distribution Factors for AC Power Flow, IJERA vol. 2, Issue4, pp , July- August [3] V.Anjaneyulu, P.V.NarasimhaRao, K.N.S.Durga Prakash. Fixed transmission cost allocation using power flow tracing methods, IJAREEIE vol. 2, Issue 8, pp ,august [4] Hemant N. Raval, Ashik IndravadanModi, Dr. Bhavik N. Suthar. Transmission Pricing in Restructured Power System Using Power Tracing, global research analysis vol.2 issue 4,pp april [5]SajjadKouhi,MehdiKhavaninzadeh,SajadNajafiRavadanegh. 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Iyambo,andR.Tzoneva Member IEEE Transient stability analysis of the IEEE 14 bus electrical power system 2007 IEEE [25] Niranjankumar, student member IEEE Y.R.V.Reddy, Devadutta das, N.P.Padhy, senior member IEEE2001 Transmission cost allocation y using MW-Mile approaches in restructured Indian power system [26]DariushShirmohammadi,MarioV.P.Pereira, power system research Some fundamental technical concepts about cost based transmission pricing 1995 IEEE [27] DariushShirmohammadi, ChithraRajagopalan, Chifong L.Thomas senior member, Cost of transmission transactions an introductcion 1991IEEE [28] J.W. Bialek and P.A. Kattuman proportional sharing assumption in tracing methodolaoggy, IEEE 2004 [29] Deregulation nptel notes. [30] The MATLAB software tutorial in [31] The power world software and case files in world.com/glover sarama overbye. AUTHORS CH.VANI: She is an M-Tech candidate at QIS college of Engineering& Technology under JNTU, Kakinada. She received her B-Tech degree from QIS Institute of Technology under JNTU Kakinada. Her current research interests are Applications on transmission systems, Power System Deregulation. J.KRISHNAKISHORE: He is an associate professor in QIS College of Engineering &Technology at Ongole. He is a Ph.D candidate. He got his M-Tech degree from JNTU Hyderabad and his B-Tech degree from RVRJC Engineering College, Guntur. His current research interests are power systems, power systems control and automation, control systems, power systems deregulation. International Journal of Electrical & Electronics Engineering 18