CHAPTER 5 LOAD BALANCING OF LOW-VOLTAGE DISTRIBUTION NETWORK BY HEURISTIC METHODOLOGY

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1 167 CHAPTER 5 LOAD BALANCING OF LOW-VOLTAGE DISTRIBUTION NETWORK BY HEURISTIC METHODOLOGY 5.1 INTRODUCTION The reduction of energy losses in the distribution of low voltage distribution network has been achieved by using fuzzy logic based load balancing in chapter 4. Though it is effective, further optimization by reducing neutral current in the LV network is attempted and explained in this chapter. This work presents load balancing using the heuristic methodology. The main task of this investigation is how unbalance due to uneven distribution of single phase loads at the secondary side of the distribution network can be minimized further, as compared with fuzzy logic based load balancing. The unequal distribution of loads between the three phases of the supply system determines the flow of unbalanced currents that produce unbalanced voltage drops on the electric lines. This increase in neutral current due to unbalance produces more line losses. Neutral flow will be less on a system that has been phase balanced. The savings from reduced neutral flow may range anywhere from thousands to millions of rupees in wasted fuel costs, depending on the scale of distribution system and the imbalances that exist. Hence this method analyzes the propagation of unbalance in LV distribution network resulting in increase of neutral current.

2 168 The suggested heuristic method reduces unbalance resulting in decrease of neutral current value and ultimately reducing the losses of LV network. Low voltage distribution systems need phase specific approach with the neutral conductor as the fourth wire due to unbalance. Hence, the analysis becomes more difficult than that of transmission systems which can be represented by single phase equivalent diagrams. Additively, actual load data collection is vitally important for the design at low voltage level. It will also give a chance to observe the basic characteristics of the load and find the consumer factors correctly. In this study, a comprehensive approach is presented for the determination of span-by-span current distribution along low voltage feeders. The actual distribution transformer with its LV network is presented in this thesis in all chapters. Hence model developed is realistic. The simulations are performed by utilizing actual data in order to take the diversity between consumers into account. The literature survey indicates the following procedures. 5.2 LITERATURE SURVEY Distribution feeder line models that can be used in power flow and short circuit analysis of balanced and unbalanced three phase distribution feeders have been presented by Kersting and Phillips (1994). The major conclusion drawn from the comparative studies is that there are significant differences in phase power losses for balanced and unbalanced operating conditions. Modeling of unbalanced three phase distribution feeders introduce large errors making modeling a tough task. Nevzat et al (1994) states that accurate determination of the neutral conductor current distribution along a low voltage feeder is vitally important due to two perspectives. The first one is to investigate the voltage profile along the feeder. The second one is directly related with the economic feasibility of the system (i.e. total losses occurred on the feeder). Results

3 169 show that the unbalance results in considerable induced voltages and currents through the neutral conductor. The suggestion of the paper is that the neutral conductor should be selected in the same size with the phase conductors as current flowing through neutral is sometimes more than the base phase current. Tsai-Hsiang Chen and Jeng Cherng (2000) present an effective approach to optimize the phase arrangement of the distribution transformers connected to a primary feeder for system unbalance improvement and loss reduction. This method is specific to Taiwan electrical utility where distribution transformer used is asymmetrical with an open wye-open delta connection to obtain a 3 phase 4 wire service and also does not handle secondary LV network. 5.3 ADVENT OF THE HEURISTIC METHODOLOGY Fuzzy logic based load balancing discussed in earlier chapter 4 takes the overall low voltage distribution network for load balancing and it balances R, Y and B phase s currents in the entire network. The results are fruitful, but it does not guarantee reduction of neutral current in each section of the network. Fuzzy logic based load balancing effects load transfer between poles by reconfiguring consumers in different poles of the selected LV network. This will balance loads in the entire network but fails to balance loads in each section of entire LV network. The approach which will guarantee reduction of neutral current in each section that is in each span length of the entire low voltage distribution network will bring down line losses to greater extent. To solve the problem arising out of unbalance current in LV network more effectively, the heuristic method has been developed, tested and validated in this thesis.

4 HEURISTIC METHOD LOAD BALANCING OF LV NETWORK Types of load conditions, load combinations and prediction of unbalance currents in LV network have been discussed earlier elaborately in the chapter 2 and chapter 4. For the different combination of loads described consumers are shifted pole-wise so that all the individual poles of the distribution transformer remains balanced after the process. By this approach, the neutral current in all sections of LV distribution network gets reduced. The flow chart explaining the procedure to shift consumers is shown in Figure 5.1. All load combinations and load conditions considered for overall LV network has been adopted for each and every pole of the LV network in which consumers (node) are connected. The objective of the switching logic is to minimize neutral current. The difference between optimum current and phase current is calculated. Each consumer s current is compared with the difference value and single consumer matching the difference value is tabulated. Similar exercise is done for sum of currents of two consumers taken at a time and three consumers taken at a time and results are tabulated. The sum of currents of consumers which almost matches the difference value is found out. The suggestion is given by consumer shifting logic to shift those consumers from overloaded phase to under loaded phase. The same logic is adopted for all the poles with connected consumers of entire LV distribution network. The entire logic has been developed in c-program.

5 171 Start Read the consumer details from the excel file and save them in the structure consumer Find the number of poles, total number of consumers and no. of consumers in each pole F For a pole, find I R, I Y and I B, sum of currents in R, Y, B phase respectively I R = I Y = I B? YES Pole is balanced NO I opt = (I R +I Y + I B )/3 Stop Find r = I R I opt y = I Y I opt b = I B I opt A Figure 5.1(a) Flow chart for Consumer Shifting Technique

6 172 A Check r, y, and b. If one of them is positive and one is negative, set case = 1. Assign corresponding phases as posphase and negphase. If two phases are positive and one is negative, set case = 2. Assign corresponding phases as posphase, posphase1 and negphase. If one phase is positive and two are negative, set case = 3. Assign corresponding phases as posphase, negphase and negphase1. Is case=1? NO B YES = posvalue Find min1 = min [ ( current of any consumer) ] C Figure 5.1(b) Flow chart for Consumer Shifting Technique

7 173 C Find min2 = min [ ( sum of currents of any two consumers) ] Find min3 = min [ ( sum of currents of any three consumers) ] Find min (min1, min2, min3) Shift the corresponding consumer(s) from posphase to negphase If there is no such consumer, print Cannot shift from posphase to negphase B Is case=2 NO D YES = posvalue YES 1 = posvalue1 E Figure 5.1(c) Flow chart for Consumer Shifting Technique

8 174 E Repeat steps of case = 1 for and 1 D Is case=3? NO Inconsistent Data YES Stop = (negvalue) 1 = (negvalue1) Repeat steps of case = 1 for 1 Find I R, I Y and I B sum of currents in R, Y, B phase after balancing Are all poles considered? YES F Stop NO Figure 5.1(d) Flow chart for Consumer Shifting Technique

9 RECONFIGURATION USING HEURISTIC METHODOLOGY Three transformers have been examined for unbalanced condition of LV network and overall balanced (between sections, between poles) condition of LV network and results are studied in chapter 4. For analyzing with heuristic method, two numbers of distribution transformers, Urban DT2 and Urban DT3 are taken for study. Load balancing is effected within sections taking into consideration all sections in the LV network. Based on the analysis, the results obtained in simulation software by reconfiguring the consumers (nodes) of Urban DT2 and Urban DT3 so as to balance the system is presented in this section. 5.6 CASE STUDY 1: RECONFIGURATION OF URBAN DT2 The schematic diagram, low voltage distribution album (LV album) and load analysis by distribution simulation package of urban DT 2 has been already presented in the section 4.6. It contains twenty poles and the consumers connected in different phases of each pole. It caters to the needs of 103 consumers with 96 single phase consumers connected in different phases R, Y, B and 7 three phase consumers with balanced loads. The inputs to the c-program are the single phase consumers for balancing suggestion. The three phase consumers are industrial consumers whose loads are already balanced. Though there are twenty poles, the c-program displays number of poles with single phase consumers. The snap shots of the consumer shifting program output for Urban DT2 are shown below. The transformer profile of Urban DT2 is shown in Figure 5.2(a). Figure 5.2(b) to Figure 5.2(j) display the status of the consumers in poles before and after balancing.

10 176 Figure 5.2(a) Urban DT2 Profile Out of 20 poles in the LV network, the consumers are connected in 13 poles. 7 numbers of three phase consumers are connected in 4 poles and 96 numbers of single phase consumers are connected in 9 poles. Unbalance is created due to the presence of 96 service connection single phase consumers in 9 poles. The total number of consumers connected in each pole is as shown in Figure 5.2(a), Urban DT2. By heuristic approach, balancing is suggested in all 9 poles as shown in below figures (Figure 5.2(b) to Figure 5.2(j)) by displaying service connection numbers of consumers to be shifted between phases in each pole.

11 177 Figure 5.2(b) Urban DT2 Pole 5 Figure 5.2(c) Urban DT2 Pole 6

12 178 Figure 5.2(d) Urban DT2 Pole 7 Figure 5.2(e) Urban DT2 Pole 8

13 179 Figure 5.2(f) Urban DT2 Pole 9 Figure 5.2(g) Urban DT2 Pole 10

14 180 Figure 5.2(h) Urban DT2 Pole 11 Figure 5.2(i) Urban DT2 Pole 16

15 181 Figure 5.2(j) Urban DT2 Pole CYMDIST Load flow Report The transformer networks are simulated for load flow under unbalanced and pole-wise balanced conditions. The load flow report of unbalanced Urban DT2 is reproduced in Table 5.1 and Table 5.2 shows the report for pole-wise balanced Urban DT2. From the tables it is observed that neutral current gets reduced in each node (pole) in pole balanced transformer. This is due to reconfiguration of consumers effected pole-wise, that is, within section, all phase currents are balanced thereby reducing the neutral current.

16 182 Table 5.1 CYMDIST Load flow Report of Unbalanced Urban DT2 Equipment No Real Power (kw) Voltage (V) I A I B I C I N Table 5.2 CYMDIST Load flow Report of Pole-Balanced Urban DT2 Equipment No Real Power (kw) Voltage (V) I A I B I C I N

17 Line Loss Report Simulation result of urban DT2 with unbalanced and pole-balanced configuration is tabulated in Table 5.3 and Table 5.4, respectively. Table 5.3 CYMDIST Summary Report of Unbalanced Urban DT2 Summary kw kvar kva PF(%) Total Generation Load read (Non-adjusted) Load used (Adjusted) Total Loads Line Losses Cable Losses Transformer Losses Total Losses Power loss in unbalanced Urban DT3 is found to be 14.31kW. After pole-balancing of the network, the power loss is found to be 8.36kW. A reduction of 41.6% is obtained. Table 5.4 Cymdist Summary Report of Pole wise Balanced Urban DT2 Summary kw kvar kva PF (%) Total Generation Load read (Non-adjusted) Load used (Adjusted) Total Loads Line Losses Cable Losses Transformer Losses Total Losses

18 184 The total power delivered from the transformer is kw and the total loss is kw which is 6.77% of total power. After load balancing the loss is arrived as 8.36kW, which is 4.0% of total power and there is significant reduction of power loss up to 2.77%. If a condition is presumed in which the transformer is operated with kw of total power for the period of 10 hours in a day then the energy delivered would be kwhr. Loss reduction of 2.72% is equivalent to 58 units which is saving met out from load balancing. An average cost of `3.20 is adopted to compute the saving per transformer. The saving per transformer is 58*3.20=185 and for one year 365*185= `67525 is arrived at. For 1,92,000 distribution transformers in one electrical utility, the total saving per year will be 67525*1,92,000= million rupees/annum. 5.7 CASE STUDY 2: RECONFIGURATION OF URBAN DT3 The schematic diagram, low voltage distribution album (LV album) and load analysis by distribution simulation package of Urban DT 3 has been already presented in the section 4.7. It contains fourteen poles and the consumers connected in different phases of each pole. It caters to the needs of 83 single phase consumers connected in different phases R, Y, B in 7 poles and 6 three phase consumers with balanced loads in 2 poles. The result of consumer shifting logic is tabulated in Table 5.5.

19 185 Table 5.5 Profile of Urban DT3 before and after Balancing S.No Optimum Current I R I Y I B I opt Phase Phase Sc NO I From To I R I Y I B B R B R B R,Y B R B Y B Y B Y 3 Pole No Before Balancing Current in Amps R B,Y R B R Y R B R B Y R,B R B,Y R Y R Y Y R Y B B R B R,Y B R B Y Y R Y R,B Y R Y B B R B R B R B 0 Over Loaded Under Loaded Consumers to be Shifted Phase Change After Balancing Current in Amps R,Y B Y B Y B Y CYMDIST Load flow Report The transformer network is simulated for load flow under unbalanced and pole-wise balanced conditions. The load flow reports of unbalanced and pole-wise balanced Urban DT3 are tabulated in Table 5.6 (reproduced from Table 4.8) and Table 5.7, respectively. From the tables, it is observed that neutral current gets reduced in each node (pole) in pole balanced load flow report compared to unbalanced load flow report.

20 186 Table 5.6 CYMDIST Load flow Report of Unbalanced Urban DT3 Equipment No Real Power (kw) Voltage (V) I A I B I C I N Table 5.7 CYMDIST Load flow Report of Pole wise Balanced Urban DT3 Equipment No Real Power (kw) Voltage (V) I A I B I C I N

21 Line Loss Report Simulation result of Urban DT3 with unbalanced and pole-balanced configuration is tabulated in Table 5.8 and Table 5.9, respectively. Table 5.8 CYMDIST Summary Report of Unbalanced Urban DT3 Summary kw kvar kva PF(%) Total Generation Load read (Non-adjusted) Load used (Adjusted) Total Loads Line Losses Cable Losses Transformer Losses Total Losses Table 5.9 CYMDIST Summary Report of Balanced Urban DT3 Summary kw kvar kva PF (%) Total Generation Load read (Non-adjusted) Load used (Adjusted) Total Loads Line Losses Cable Losses Transformer Losses Total Losses The power loss in unbalanced Urban DT3 is found to be 7.13kW. After pole-balancing of the network, the power loss is found to be 4.11kW. A reduction of 42.3% is obtained. The total power delivered from the

22 188 transformer is kw and the total loss is 7.13 kw which is 3.7% of total power. After load balancing the loss is arrived as 4.11kW, which is 2.1% of total power and there is reduction of power loss up to 1.6%. If a condition is presumed in which the transformer is operated with kw of total power for the period of 10 hours in a day then the unit delivered would be kwhr. The loss reduction of 1.6% is 31 units which is saving met out from load balancing. The average cost of Rs.3.20 is adopted to compute the saving per transformer. The saving per transformer for one year 365*99= `36135 is arrived at. For 1,92,000 distribution transformers in one electrical utility the total saving per year will be 36135*1,92,000 = million rupees/annum. In this thesis, a complete off-line package has been designed by using heuristic methodology. The proposed load balancing technique effectively meets the criteria to minimize energy loss which has been proved by CYMDIST simulation. On an average, 41% power loss reduction is accomplished in the case studies undertaken. Significant reduction in energy losses and hence a huge savings in cost is ascertained by the aforesaid approach. Both the distribution transformers taken as case study belong to urban area. Hence they represent worst-case study for the proof of the method. If rural area or semi-urban area distribution transformer is load balanced using heuristic method, the result will be very much beneficial to electrical utility due to the presence of lengthy distribution lines in LV network and scattered consumers.