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40220140503002
40220140503002
40220140503002
40220140503002
40220140503002
40220140503002
40220140503002
40220140503002
40220140503002
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  • 1. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 3, March (2014), pp. 05-13 © IAEME 5 OPTIMAL ALLOCATION OF CAPACITOR IN A RADIAL DISTRIBUTION SYSTEM USING LOSS SENSITIVITY FACTOR AND HARMONY SEARCH ALGORITHM Priyanka Das1 , S Banerjee2 Department of Electrical Engineering, Dr. B.C Roy Engineering College, Durgapur West Bengal, India ABSTRACT Minimization of active power loss in distribution systems is very essential to raise the overall efficiency of power system. This article presents a method of reducing the loss by placing shunt capacitors. Here two stage methods have been proposed for optimal allocation of capacitor in a radial distribution system. In first stage loss sensitivity factor is used to calculate the location and secondly the harmony search algorithm is used for cost minimization including capacitor cost and cost due to power loss. The proposed method is tested on 33-bus and 69-bus system and results are given below. Keywords: Harmony search algorithm, Loss sensitivity factor, Radial distribution system, Shunt capacitors. 1. INTRODUCTION Now a day with increase in load demand, the distribution system is becoming more complex and due to increase in loads it tends to increase the systems losses and for that reason the voltage profile is decreasing badly. At heavily loaded conditions the reactive power flow causes significant losses and also causes reduction in voltage level .So it is the duty of an electrical engineer in distribution companies to minimize the power loss and also to increase the voltage profile. To reduce the power loss and to increase the voltage profile the use of shunt capacitor is the best and reliable option as it provides reactive compensation. The shunt capacitor should be optimally sized and placed that it should be able to reduce the power loss and can enhance the voltage profile of the system. Minimization of loss will increase the life span of the distribution network and reliability of the system. Optimal allocation of capacitor deals with the appropriate location where the capacitor to be placed, type of the capacitor ,size of the capacitor and the total number of the capacitor that INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING & TECHNOLOGY (IJEET) ISSN 0976 – 6545(Print) ISSN 0976 – 6553(Online) Volume 5, Issue 3, March (2014), pp. 05-13 © IAEME: www.iaeme.com/ijeet.asp Journal Impact Factor (2014): 6.8310 (Calculated by GISI) www.jifactor.com IJEET © I A E M E
  • 2. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 3, March (2014), pp. 05-13 © IAEME 6 should be placed so that the total cost should be minimized without violating the operational constraints. With the development in optimization many research work has been done on this topic. Numerous optimization techniques have been used by researchers to optimally allocate the capacitor in a radial distribution system. They are classified into four groups, analytical methods, numerical programming methods, heuristic methods and meta-heuristic methods. The early proposed approaches are the analytical numerical programming techniques like local variation methods [1] and mixed integer linear programming techniques [2,3] have been introduced for solving the problem of capacitor sizing and allocation. In recent years, the most popular meta- heuristic approaches have been introduced for the VAr planning problem study. The authors who used meta-heuristics methods we find, Huang et al. [4] They have solved the capacitors optimal placement using an immune multi-objective algorithm. They have modeled the objective functions by fuzzy logic (FL).The method provides us a set of feasible solutions. Bhattacharya and coauthors [5] have introduced a FL-based simulated annealing (SA) method to find the optimal sizes of capacitor. Using FL the suitable locations are identified and their sizes are obtained using SA by Prakash et al. [6] have also used a hybrid method where the capacitor suitable places are determined by means of loss sensitivity factors. The optimal sizes, considered as continuous variables, are determined using particle swarm optimization (PSO) algorithm. To determine the fixed and switched capacitor sizes, Das [7] has suggested a genetic algorithm (GA) based FL approach to maximize the net savings and minimize node voltage deviations. The two objectives are first fuzzified and integrated into a fuzzy global objective function through appropriate weighting factors. The weighting factors are optimized by GA. On the other hand, Seifi et al. [8] in their FL–GA hybrid technique have used the fuzzy reasoning to find the best capacitor locations and GA, for finding the optimal weighting factors of the voltage and the power losses exponential membership functions. The capacitor optimal size is that, among the available standard capacitors, giving the best objective function. Abdelaziz et al. [9] have proposed a method based on fuzzy expert systems to select the best candidate nodes for receiving capacitors in order to maximize the power loss reduction and total net savings. For the total power loss minimization they have determined the optimal locations and tapping ratio for voltage regulator. 2. PROBLEM FORMULATION Here the main objective is to minimize the total cost due to real power loss and capacitor installation. To solve the capacitor placement and sizing problem the following objective function has been taken. Min f =min (COST) (1) where COST is the objective function which includes the cost of power loss and capacitor placement. The voltage magnitude at each bus must be maintained within its limit and can be expressed as V min ≤│Vi│≤ V max (2) Where │Vi│ is the voltage magnitude at bus i and V min and V max are the minimum and maximum voltage limits respectively .For the calculation of power flows the following sets of simplified recursive equations which are derived from single line diagram are shown in fig 1. Pi+1 = Pi – PLi+1 – Ri,i+1 . (3)
  • 3. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 3, March (2014), pp. 05-13 © IAEME 7 Q i+1 = Q i – Q i+1 – X i+1 . (4) │ V i+1 2 │=│ Vi 2 │- 2 (R i, i+1 .Pi + X i ,i+1 .Q i )+(R i ,i+1 2 + Q i ,i+1 2 ) . (5) Where P i and Q i are the real and reactive power flowing out of bus i ,P Li and Q Li are the real and reactive load powers at bus i. The resistance and reactance of the line section between bus i and i+1 are denoted by R i ,i+1 and X i,i+1. The power loss of the line section connecting the buses i and i+1 may be calculated as: P LOSS ( i ,i+1 )= R i ,i+1 . (6) Fig1. Single line diagram of main feeder The total power loss of the feeder PT,LOSS can be computed by summing up the losses of all the line sections of the feeder, and given as PT, LOSS = (7) The total cost due to capacitor placement and power loss change is given by: COST = K p .PT, LOSS+ (8) Where n is the number of candidate locations for capacitor placement K p is the equivalent annual cost per unit of power loss in $/( K w year ); Kcf is the fixed cost for the capacitor placement. The constant Ki c is the annual capacitor installation cost, and, i = 1, 2, . . . , n are the indices of the buses selected for compensation. K p = 168$ / (kw year) and Kcf = 1000$ are taken. 2.1 Constraints Each capacitor size minimizing the objective function, must verify the equality and inequality constraints. Two inequality constraints are considered here for capacitor placement that must be satisfied are as such: (I) V min ≤ │Vi│≤ V max (9)
  • 4. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 3, March (2014), pp. 05-13 © IAEME 8 (II) Capacitors are available in discrete sizes. So, shunt capacitors are to be dealt with multiple integers of the smallest capacitor size available and it may mathematically be expressed as: Q c i ≤ L Qs L = 1,2,3 …. , nc (10) where nc is number of shunt capacitors, Q c i is the kVAr rating of capacitor installed at the ith bus and Qs smallest capacitor size available. 2.2 Sensitivity Analysis and Loss Sensitivity Factors By using loss sensitivity factors the candidate nodes for the capacitor placement is determined. By estimation of these candidate nodes it helps in the reduction of search space for optimization problem. Considering a distribution line with an impedance R +j X and a load Peff and Q eff connected between buses p and q is given by. Active power loss can be given by in (3) is rewritten for kth line between buses p and q as Plineloss [q] = (11) Similarly the reactive power loss in the kth line is given by QLineloss[q ] = (12) Where P eff [q] = Total effective active power supplied beyond the node ‘q’. Qeff[q]= Total effective reactive power supplied beyond the node ‘q’. Both the loss sensitivity factor can be given as: = (13) = (14) 2.3. Candidate node selection using loss sensitivity factors The Loss Sensitivity Factors ( ) are calculated from the base case load flows and the values are arranged in descending order for all the lines of the given system. A vector bus position ‘bpos [i]’ is used to store the respective ‘end’ buses of the lines arranged in descending order of the values ( ).The descending order of ( ) elements of ‘‘bpos[i]’ vector will decide the sequence in which the buses are to be considered for compensation. This sequence is purely governed by the (
  • 5. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 3, March (2014), pp. 05-13 © IAEME 9 ) and hence the proposed ‘Loss Sensitive Coefficient’ factors become very powerful and useful in capacitor allocation or Placement. At these buses of ‘bpos [i]’ vector, normalized voltage magnitudes are calculated by considering the base case voltage magnitudes given by (norm[i] = V[i]/0.95). Now for the buses whose norm[i] value is less than 1.01 are considered as the candidate buses requiring the Capacitor Placement. These candidate buses are stored in ‘rank bus’ vector. It is worth note that the ‘Loss Sensitivity factors’ decide the sequence in which buses are to be considered for compensation placement and the ‘norm[i]’ decides whether the buses needs Q-Compensation or not. If the voltage at a bus in the sequence list is healthy (i.e., norm[i] > 1.01) such bus needs no compensation and that bus will not be listed in the ‘rank bus’ vector. The ‘rank bus’ vector offers the information about the possible potential or candidate buses for capacitor placement. 3. HARMONY SEARCH ALGORITHM Harmony Search is a relatively new population-based meta-heuristic algorithm. In the field of engineering optimization it has shown excellent results. It deals with the behavior of an orchestra where main objective of the musician is to compose the most harmonious melody, as measured by aesthetic quality. While comparing the process of improvisation by musicians with the optimization process, we can realize that each musician corresponds to a decision variable; the pitch of each instrument determines the aesthetic quality, just as the objective function value is determined by the set of values assigned to each decision variable. After improvisation, the musical harmony corresponds to the solution vector at a particular iteration. Iteration to iteration it, enhances the fitness of the solution vector. The Optimization procedure of an HS algorithm steps are as follows: Step 1: Initialize the optimization problem and algorithm parameters. Step 2: Initialize the harmony memory (HM). Step 3: Improvise a new harmony from the HM. Step 4: Update the HM. Step 5: Repeat Steps 3 and 4 until the termination criterion is satisfied. For explanation of Harmony Search in more detail, we have to first idealize the Improvisation process by a skilled musician. For improvising, he or she has three possible choices: (1) play any famous piece of music (a series of Pitches in harmony) exactly from his or her memory; (2) play something similar to a known piece (thus adjusting the pitch slightly); or (3) compose new or random notes. Zong Woo Geem et al. And formalized these three options into quantitative optimization process in 2001, and the three corresponding components become: usage Memory is important, and is similar to the choice of the best-fit individuals in genetic algorithms (GA). And this will ensure that the best harmonies will be carried over to the New Harmony memory. For the memory usage more effectively, it is typically assigned as a parameter r accept [0, 1], called harmony memory accepting or considering rate. If this rate is too low, only few best harmonies are selected and it may converge too slowly. If this rate is extremely high (near 1), almost all the harmonies are used in the harmony memory, then other harmonies are not explored well, leading to potentially wrong solutions. Therefore, typically, we use r accept=0.7 ~ 0.95. The second component is the pitch adjustment determined by a pitch bandwidth b range and a pitch adjusting rate r pa. Though in music, pitch adjustment means to change the frequencies, it corresponds to generate a slightly different solution in the Harmony Search algorithm [10]. In theory, the pitch can be adjusted linearly or nonlinearly, but in practice, linear adjustment is used. So we have x new= x old + b range* € where x old is the existing pitch or solution from the harmony memory, and x new is the new pitch after the pitch adjusting action. This essentially produces a new solution around the existing quality solution by varying the pitch slightly by a small random amount [11, 12]. Here € is a random number generator
  • 6. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 3, March (2014), pp. 05-13 © IAEME 10 in the range of [-1, 1]. Pitch adjustment is similar to the mutation operator in genetic algorithms. We can assign a pitch-adjusting rate (r pa) to control the degree of the adjustment. A low pitch adjusting rate with a narrow bandwidth can slow down the convergence of HS because the limitation in the exploration of only a small subspace of the whole search space. On the other hand, a very high pitch- adjusting rate with a wide bandwidth may cause the solution to scatter around some potential optima as in a random search. Thus, we usually use r pa=0.1 ~0.5 in most applications begin Objective function f(x), x=(x1, x2 , …, xd)T Generate initial harmonics (real number arrays) Define pitch adjusting rate (r pa), pitch limits and bandwidth Define harmony memory accepting rate (r accept) while ( t<Max number of iterations ) Generate harmonics by accepting best harmonics Adjust pitch to get new harmonics (solutions) if (rand>r accept), choose an existing harmonic randomly else if (rand>r pa), adjust the pitch randomly within limits else generate new harmonics via randomization end if Accept the new harmonics (solutions) if better end while Find the current best solutions end Fig 2: Pseudo code of the Harmony Search algorithm The third component is the randomization, which is to increase the diversity of the solutions. Although adjusting pitch has a similar role, but it is limited to certain local pitch adjustment and thus corresponds to a local search. The use of randomization can drive the system further to explore various diverse solutions so as to find the global optimality. The three components in harmony search can be summarized as the pseudo code shown in Fig. 2. In this pseudo code, we can see that the probability of randomization is P random =1−r accept (15) the actual probability of adjusting pitches is P pitch =r Accept *r pa (16) 4. PROPOSED OPTIMAL CAPACITOR PLACEMENT METHODOLOGY Here in this proposed method the HS algorithm is applied as an optimization technique to determine the optimal size of the capacitor at the buses. Power flow is used for the computation of power loss. The procedures for implementation of the proposed optimal capacitor placement method has been described in two stages are as follows: Harmony Search
  • 7. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 3, March (2014), pp. 05-13 © IAEME 11 Determination of candidate location Step1: Input all the parameters like line data and load data. Step2: Run the load flow as explained above by using set of simplified recursive equation. Step3: Calculate the loss sensitivity factor. Step4: Select the buses whose norm[i] value is less than 1.01 as candidate location. Optimization using HARMONY SEARCH algorithm Step1: Initialize all the parameters of the Harmony search algorithm. Like Qc min and Qc max, (minimum and maximum limits for capacitor sizes), hms, HMCR, PAR min , PAR max. Step2: Initialize the harmony memory i.e. create [hms x n] number of initial solutions randomly within the limits ,where hms is the harmony memory size and n is the number of capacitors. Step3: Place all the n capacitors of the harmony vector i.e each row of the Harmony vector at the respective optimal capacitor location and perform the load flow and find the total real power loss after placement. Step4: Compute the capacitor cost. Step5: Compute the total cost (fitness function) using equation (8) Step6: Repeat the same procedure for all the rows of the harmony vector to to find fitness functions. Step7: Obtain the best fitness function by comparing all the fitness functions. Step8: Start the improvisation (Iteration count is set to one) Step9: Improvisation of the New Harmony is generating a New Harmony, A New Harmony vector is generated based on the following steps: (i)Random selection: It is used to select one value randomly for a certain element of the new vector from the possible range (QC min, QC max) of values. (17) (ii) Memory consideration: It is used to choose the value for a certain element of the new vector from the specified HM range. x’i = x'i є {x'1, x'2, xHMS i} with probability HMCR x’i = x’i є Xi with probability (1-HMCR) (18) Step 10: Pitch adjustment It is used to adjust the values of the New Harmony vector obtained in step 7. (Between PAR min and PAR max ). x'i = x'i ± rand (0,1)* bw (19) (bw - band width varies between a higher value and a lower value from first iteration to last iteration) Step 11: Find the fitness values corresponding to the New Harmony generated and pitch adjusted in steps (18) and (19). Step 12: Apply Greedy Search between old harmony and New Harmony by comparing fitness functions. Step 13: Update harmony memory, by replacing the worst harmony with the new best Harmony. Obtain the best fitness function by comparing all the fitness functions. Step 14: The improvisation (iteration) count is incremented and if iteration count is not reached the maximum then go to step 9. Step 15: The solution vector corresponding to the best fitness function gives the optimal capacitor sizes in n optimal locations.
  • 8. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 3, March (2014), pp. 05-13 © IAEME 12 5. RESULTS Loss sensitivity factor is used to calculate the candidate location for the capacitor placement and HSA is used to find the optimal capacitor size. In this work, hms = 60, HMCR=90%, Number of iterations 500, PAR min = 0.4 and PAR max = 0.9. 5.1. Results of 33-bus system The proposed algorithm is applied to 33-bus system [13]. Optimal capacitor locations are identified based on the Loss sensitivity factor values. For this 33-bus system, one optimal location is identified. Capacitor size in that optimal location, total real power losses before and after compensation, voltage profile before and after compensation and total annual cost before and after compensation are shown below in Table1. BUS NO; 6 CAPACITOR SIZE in ( KVAR) 1800 TOTAL REAL POWER LOSS in (KW) before compensation. 201.8588 TOTAL REAL POWER LOSS in (KW) after compensation. 147.0588 VOLTAGE IN P.U at bus number 6 before compensation. 0.9499 VOLTAGE IN P.U at bus number 6 after compensation 0.9676 TOTAL ANNUAL COST before compensation 40573.62$ TOTAL ANNUAL COST after compensation 26246.11$ LOSS REDUCTION 54.8 LOSS REDUCTION % 27.147% 5.2. Results of 69-bus system The proposed algorithm is applied to 69-bus system [14]. Optimal capacitor location is identified based on the Loss sensitivity factor values. For this 69-bus system, one optimal location is identified. Capacitor sizes in that optimal location, total real power losses before and after compensation, voltage profile before and after compensation, total annual cost before and after compensation are shown below in Table-2. BUS NO; 61 CAPACITOR SIZE in ( KVAR) 1350 TOTAL REAL POWER LOSS in(KW) before compensation 224.5407 TOTAL REAL POWER LOSS in (KW) after compensation 172.4137 VOLTAGE IN P.U at bus number 6 before compensation 0.9133 VOLTAGE IN P.U at bus number 6 after compensation 0.9364 TOTAL ANNUAL COST before compensation 37722.83$ TOTAL ANNUAL COST after compensation 30166.54$ LOSS REDUCTION 51.1264 LOSS REDUCTION % 22.76%
  • 9. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 3, March (2014), pp. 05-13 © IAEME 13 6. CONCLUSION Here in this paper a two- stage method L.S.F and HS algorithm has been successfully applied for capacitor placement. By the installation of shunt capacitor at the optimal position there is a significant decrease in power loss, decrease in total annual cost and increase in voltage profile. So the combination of both Loss sensitivity factor and HS algorithm yields good results. 7. REFERENCES [1] Ponnavaiko M, Prakasa Rao KS. Optimal choice of fixed and switched shunt capacitors on radial distributors by the method of local variations. IEEE Trans Power App Syst 1989;102:725–34. [2] Baran ME, Wu FF. Optimal capacitor placement on radial distribution systems. IEEE Trans Power Delivery 1989;4:725–34. [3] Khodr HM, Olsina FG, De Oliveira-De Jesus PM, Yusta JM. Maximum savings approach for location and sizing of capacitors in distribution systems. Elect Power Syst Res 2008; 78:1192–203. [4] Huang TL, Hsiao YT, Chang CH, Jiang JA. Optimal placement of capacitors in distribution systems using an immune multi-objective algorithm. Elect Power Energy Syst 2008; 30: 184–92. [5] Bhattacharya SK, Goswami SK. A new fuzzy based solution of the capacitor placement in radial distribution system. Exp Syst App 2009; 36:4207–12. [6] Prakash K. Particle swarm based capacitor placement on radial distribution systems. In: Power Eng. Soc. gen. meeting, Tampa, TL; 24–28 June 2007. p. 1–5. [7] Das D. Optimal placement of capacitors in distribution system using fuzzy-GA method. Elect Power Energy Syst 2008;30:361–7. [8] Seifi A, Hesamzadeh MR. A hybrid optimization approach for distribution capacitor allocation considering varying load conditions. Elect Power Energy Syst 2009;31:589–95. [9] Abdelaziz AY, Mekhamer SF, Nada MH. A fuzzy expert systems for loss reduction and voltage control in radial distribution systems. Elect Power Sys Res 2010;80:893–7. [10] Haque MH. Capacitor placement in radial distribution systems for loss reduction IEE Proc Gener Trans Distrib 1999;146:501–5. [11] Baran M.E. and Wu F.F. 1989. Network reconfiguration in distribution systems for loss reduction and load balancing. IEEE Transactions on Power Delivery. 4(2): 1401-1407, April. [12] Baran M.E. and Wu F.F. 1989. Optimal capacitor placement on radial distribution systems. IEEE Transactions on Power Delivery. 4(1): 725-734, January. [13] Geem ZW, Kim JH and Loganathan GV (2001) A new heuristic optimization algorithm: Harmony search. Simulation, 76:60-68. [14] Lee KS and Geem ZW (2005) A new meta-heuristic algorithm for continuous engineering optimization: harmony search theory and practice. Comput. Methods Appl. Mech. Engrg., 194:3902-3933. [15] Dr.K.Ravichandrudu, G.Jyothi, P.Yohan Babu and G.V.P.Anjaneyulu, “Artificial Bee Colony Algorithm Based Approach for Capacitor Allocation in Unbalanced Radial Distribution Systems”, International Journal of Electrical Engineering & Technology (IJEET), Volume 4, Issue 4, 2013, pp. 67 - 73, ISSN Print : 0976-6545, ISSN Online: 0976-6553. [16] Nagaraju.Annam, Dr.J. Bhagwan Reddy and Dr. Sardar Ali, “A Strategic Wind Form Integration Method to Polluted Distibuted System with Shunt Capacitor”, International Journal of Advanced Research in Engineering & Technology (IJARET), Volume 4, Issue 3, 2013, pp. 147 - 157, ISSN Print: 0976-6480, ISSN Online: 0976-6499.

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