Canadian Journal on Electrical and Electronics Engineering Vol. 2, No. 8, August 2011
Reconfiguration and Load Balancing By Software Simulation In A Real Distribution Network for Loss Reduction H. Bagheri Tolabi , M. Gandomkar and M. Bahreyni Borujeni.
Abstract — To get the distribution network to operate at its minimum loss optimum performance, reconfiguration was been proposed and researched. Considering, however, that optimum performance implies minimum loss, no overloading of transformers and cables, correct voltage profile, and absence of phase voltage and current imbalances, network reconfiguration alone is insufficient. It has to be complemented with techniques for phase rearrangement between the distribution transformer banks and the specific primary feeder with a radial structure and dynamic phase and load balancing along a feeder with a radial structure. This paper contributes such a technique at the medium-voltage level of a distribution network with reconfiguration. This paper introduces a CYMEDIST based analysis for the phase balancing/loss minimization problem. An application example of the proposed analysis has been applied to Khorramabad city's MV distribution network. Key Words — load balancing, power loss, reconfiguration, MV distribution system.
I. INTRODUCTION studies show that a considerable part of the losses in power systems is related to the electricity distribution network . There are several ways to reduce losses in distribution system . Many of methods need the new equipment installed within the system in addition to the financial burden for companies, it is possible new errors produce in network and due to disturbances in their services . One of the ways of reducing losses in the distribution network is reconfiguration of MV distribution network . reconfiguration is a simple and cheap way for loss reduction in distribution systems because we don’t need to invest capital and set up new equipment in system . we can reduce the losses only by change the state of existing switches. there are many goals for reconfiguration of distribution systems such as : 1- reconfiguration in order to loss reduction.
3- reconfiguration in order to increase stability and improving voltage profile . 4- reconfiguration in order to increase reliability of network . 5- reconfiguration in order to minimizing the times cutting off electrical current for services and … II. PROBLEM DESCRIPTION AND FORMULATION The distribution system is the final stage in the transfer of power to individual customers. Typically, it commences from the secondary of the sub-transmission station transformers, and normally consists of two levels – primary distribution or medium voltage (MV) level, and the secondary distribution or low voltage (LV) level. There are two types of switch in primary distribution systems: normally closed switch which connects line sections, and normally open switch on the tie-lines which connects two primary feeders, or two substations or loop-type laterals. Network reconfiguration(or feeder reconfiguration) is the process of altering the topological structures of the distribution feeders by changing the open/close status of the sectionalizing and tie switch [1]. In general, distribution loads show different characteristics according to their corresponding distribution lines and line sections. Therefore, load levels for each time period can be regarded as non identical. In the case of a distribution system with some overloaded and some lightly loaded branches, there is the need to reconfigure the system such that loads are transferred from the heavily loaded to less loaded feeders. The maximum load current which the feeder conductor can take may be considered as the reference. Nevertheless, the transfer of load must be such that a certain predefined objective is satisfied. In this case, the objective is to ensure the network has minimum real power loss. Consequently, reconfiguration may be redefined as the rearrangement of the network such as to minimize the total real power losses arising from line branches. Mathematically, the total power loss can be expressed as follows [7]–[9]: L
∑ ri i =1
2
2
i
i
P +Q V i
(1) H.Bagheri tolabi, with Islamic Azad university Khorramabad branch, Iran (e-mail:
[email protected]). M.Gandomkar is currently lecturer of Islamic Azad university Saveh branch , Iran.
2- reconfiguration in order to load balancing.
V where
min i
max
≤ V i ≤V i
ri , P , Q and V are respectively, the resistance, real i i i
power, reactive power, and voltage of branch , and L is the 386
Canadian Journal on Electrical and Electronics Engineering Vol. 2, No. 8, August 2011 total number of branches in the system. The aim of this study is to minimize the power loss represented by (1) subject to the following constraints. The voltage magnitude of each node of each branch must lie within a permissible range. Here a branch can be a transformer, a line section or a tie line with a sectionalizing switch. III. The information needed to design 20kv khorramabad single line diagram in CYMDIST software environment For simulation MV distribution network of Khorram Abad in software environment and attention to the equations (1) in previous section, the necessary information are included details of local and electrical conditions of feeders , stations and substations , the impedance of lines , load of transformers, and … . we received them from Electricity Distribution Company of Lorestan . Due to the large volume of the information ,as an example the limited information from a station listed in table 1.
Figure 1. 20kv single line diagram of khoramabad in software environment
TABLE I INITIAL INFORMATION OF SAMPLE STATION
TABLE 2 REPORT OF LOSSES FOR A SAMPLE FEEDER IN THE
End of line charahban k parkeshahr ostandari Goldashte gharbi poshteh ghaziabad meidan
SOFTWRAE ENVIRONMENT
Total length (KM)
Peak of load (A)
feeder
8.5 5.7 5.6
210 165 110
shagayeg saheli maicrowave
17 4.7 4.7 3.5
170 190 120 70
goldasht poshteh koyefelstin shariati
station
ghaziabad 20 MVA
IV. simulation of 20kv network in CYME software
B. reconfiguration for network Initial Results
environment First considering received information such as the kinds of impedances, peak load of buses, properties of lines, distances, switches and …,the single line diagram with all details was designed, which can be seen in figure 1 . A. power flow analysis and calculate the losses before reconfiguration with complete information of network in the software environment, after power flow analysis on feeders, the total amount of losses under the title "losses before reconfiguration" calculated that was nearly equivalent to 4066 kw. Due to large number of feeders ,for example one report loss of the "goldasht" feeder is shown in table 2 . its loss is about 196.8 kw.
The network reconfiguration operates with opening and closing 4 suitable switches. Beginning with opening the 14408NH 47320 key and closing 14408 SB 46020 key, some of load would be transferred from one feeder to another, and losses will be reduced a little. finally with the opening 12403NH53610 key and closing 1240NH53530 key losses reduce about 116 kw . Entirely, in this reconfiguration amount of loss reduction is about 2.87 percent .the results are shown in tables 3 and 4 .the proposed keys schematic on single line diagram can be seen in in figures 2 and 3 .
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TABLE 3 REPORT OF SWITCHES POSITION IN INITIAL RECONFIGURATION
Canadian Journal on Electrical and Electronics Engineering Vol. 2, No. 8, August 2011
C. Renewed reconfiguration with proposed keys by the TABLE 4 REPORT OF INITIAL RECONFIGURATION AND REDUCTION OF LOSSES
software With a renewed reconfiguration and put 20 number of proposed keys by the software in new positions ,the amount of total losses will be reduced. the proposed keys in the table 5 and report of loss reduction in the table 6 are shown. with renewed reconfiguration the loss will be minimized and reduced about 6.34 percent . you can see the complete report in the appendix of this article. due to a large number proposed keys on single line diagram ,we ignore showing all of their schematics and the keys 3 ,4 ,5,16 and 17th will be represented in figures 4 and 5.
TABLE 6 REPORT OF RENEWED RECONFIGURATION AND REDUCTION OF LOSSES
Figure 2. schematic of 1 and 2 keys in the initial reconfiguration
Figure 4. schematic of 4 and 16 keys in the renewed reconfiguration
Figure 3. schematic of 3 and 4 keys in the initial reconfiguration
TABLE 5 REPORT OF SWITCHES POSITION IN RENEWED RECONFIGURATION
Figure 5. schematic of 3, 5 and 17 keys in the renewed reconfiguration
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Canadian Journal on Electrical and Electronics Engineering Vol. 2, No. 8, August 2011 B) After reconfiguration
V. Optimum reconfiguration and load balancing in the network We can see load imbalance of phases in Abnormal Conditions report before reconfiguration. After the optimal reconfiguration and power flow analysis the load imbalances and consequently total losses will be reduced . as an example , you can see the condition of "Parkesaheli" feeder before and after load balancing in tables 7, A and B. after reconfiguration in this feeder, the number of overloads and low voltages consecutive will be decrease from 8 and 6 to 6 and 4 numbers, and total losses will be reduce about 4.58 kw.
VI. CONCLUSIONS In this paper, we study and simulate the Khorramabad MV distribution network in CYMDIST software and calculate total losses and load imbalance by power flow analysis before and after optimal reconfiguration .results show that the total losses and load imbalances will be reduced by suitable switch optimization . With a renewed reconfiguration and put the 20 number of proposed keys by software in new positions ,the amount of total losses will be reduced maximally .
TABLES 7 (A AND B) REPORT OF LOAD IMBALANCES AND RELEVANT LOSSES IN PARKSAHELI FEEDER
A) before reconfiguration
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APPENDIX Full report of renewed reconfiguration by the software proposed keys relevant IV.C part.
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[4] C. B. Alexandre, A. Carlos, and Newton, “Main chain representation for evolutionary algorithms applied to distribution system reconfiguration,” IEEE Trans. Power Syst., vol. 20, no. 1, pp. 206–212, Feb. 2005. [5] M. E. Baran and F. F.Wu, “Network reconfiguration in distribution systems for loss reduction and load balancing,” IEEE Trans. Power Del., vol. 7, no. 2, pp. 1401–1407, Apr. 1989. [6] M. Siti, A. A. Jimoh, and D. Nicolae, “Load balancing in distribution feeder through reconfiguration,” presented at the IECON, Raleigh, NC, Nov. 6-12, 2005. [7] M. Siti and A. A. Jimoh, “Reconfiguration circuit loss minimization through feeder reconfiguration,” presented at the SAUPEC Conf., Stellnbosch, South Africa, 2004. [8] Ukil, M. Siti, and J. Jordaan, “Feeder load balancing using neural network,”presented at the Int. Symp. Neural Networks, Chengdu, China, May 28-31, 2006.
[9] Matlab Documentation – Neural Network Toolbox MathWorks, Natick, MA, 2002, 0.180913a, Release 13, 6.5. [10] C. S. Chen and M. Y. Cho, “Energy loss reduction by critical switches, of distribution feeders for loss minimization,” IEEE Trans. Power Del., vol. 4, no. 3, pp. 1246–1253, Jul. 1992. [11] X. Yang, S. P. Carull, and K. Miu, “Reconfiguration distribution automation and control laboratory: Multiphase radial power flow experiment,” IEEE Trans. Power Syst., vol. 20, no. 3, pp. 2156–2166, Aug. 2005. [12] A. Auguglio, L. Dusonchet, and M. Giuseppe, “Minimum losses reconfiguration of MV distribution networks through local control of tie-switches,” IEEE Trans. Power Del., vol. 18, no. 3, pp. 762–771, Jul. 2003. [13] H. Salazar, R. Gallego, and R. Romero, “Artificial neural networks and clustering techniques applied in the reconfiguration of distribution systems,” IEEE Trans. Power Del., vol. 21, no. 3, pp. 1735–1742, Jul. 2006. [14] H. Kim, Y. Ko, and K.-H. Jung, “Artficial neural-network based feeder reconfiguration for loss reduction in distribution systems,” IEEE Trans.
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BIOGRAPHIES
Canadian Journal on Electrical and Electronics Engineering Vol. 2, No. 8, August 2011 Majid. Gandomkar:He was born in the Saveh from IRAN. He is PHD degree of Electrical Engineering from Science and Research Branch of Islamic azad university.his research interests are distribution systems, DG systems ,optimization and etc. Now, he is assistant professor at Islamic azad university, Saveh branch.
Hajar.Bagheri Tolabi: She was born in the Khorramabad from IRAN. She received her B.Sc. degree Electrical Engineering field in 2005 of the Bu-Ali Sina University and M.Sc on power engineering of Saveh branch Azad University in 2009. Her research interests are included distribution systems, optimization , renewable energy.
Mohammad.Bahreini Borujeni: He is electrical engineer and now the Director of Electricity Distribution Company of Lorestan. his research interests are distribution systems and power systems.
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