Electric Power Systems Research 81 (2011) 282–289 Contents lists available at ScienceDirect Electric Power Systems Research journal homepage: www.elsevier.com/locate/epsr A new heuristic approach for optimal reconfiguration in distribution systems Ahmed R. Abul’Wafa ∗ Ain Shams University, Electric Power and Machines, El Sarayat st, Abbasia, Cairo, Egypt article info Article history: Received 16 June 2010 Received in revised form 5 September 2010 Accepted 15 September 2010 Available online 15 October 2010 Keywords: Distribution system reconfiguration Power loss reduction Heuristic technique Graph theory abstract This paper presents a novel approach for optimal reconfiguration of radial distribution systems. As an integral part of the distribution system configuration, a load flow algorithm based on graph theory is pre- sented. The algorithm follows changes in system structure by traversing a directed graph of the system to find the depth-first search discovery order. For each switching-iteration, this discovery order gener- ates down-stream-nodes vectors necessary for dynamic generation of two matrices: one is the branch node incidence matrix and the other the relationship between the bus current injection and branch cur- rents. Thus avoiding creation of unconnected branches or forming closed loops. The developed load flow program is integrated with known heuristic techniques in a new heuristic search methodology for deter- mining the minimum loss configuration of a radial distribution system. The technique consists of two parts; one is to determine the best switching combinations in all loops with minimum computational effort while the other is a power loss and voltage profile calculation of the best switching combination found in part one by load flows. Compared to other published articles, the efficient developed load flow reduces the switching combinations searched and gives the optimum solution in few number of load flow runs. To demonstrate the validity of the proposed algorithm, computer simulations are carried out on 33-bus system. The results show that the performance of the proposed method is better than that of the other methods. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Distribution systems deliver power to the customers from a set of distribution substations. There are two types of switches used in primary distribution systems; sectionalize switches (nor- mally closed) and tie-switches (normally open). They are designed for both protection and configuration management in the system. Under normal operating conditions, feeders are frequently recon- figured by changing the open/closed state of each switch in order to reduce line losses and improve voltage profile. Since there are many candidate-switching combinations possible in a distribution system, finding the operating network reconfiguration becomes a complicated combinatorial, non-differentiable constrained opti- mization problem. In such system the possible number of switching combinations is 3 m , where m is the total number of tie switches in the system. However, investigating all possible options are not practicable, as they require long computational time for line loss calculation. The radial constraint and discrete nature of the switches pre- vent the use of classical techniques to solve the reconfiguration problem. Most of the algorithms in the literature are based on heuristic search techniques. Distribution system reconfiguration ∗ Corresponding author. Tel.: +20 222639022; fax: +20 222639022. E-mail address: wafaahmedrizk@gmail.com. for loss reduction was first proposed by Merlin and Back [1]. They employed a blend of optimization and heuristics to determine the minimal-loss operating configuration for the distribution system represented by a spanning tree structure at a specific load condi- tion. Since then, many techniques have been proposed. A branch and bound type heuristic algorithm was suggested by Civanlar et al. [2], where a simple formula was developed for determination of change in power loss due to a branch exchange. Shirmoham- mdi and Hong [3] applied optimal power flow analysis to network reconfiguration for loss minimization. Baran and Wu [4] proposed an algorithm to identify branches to be exchanged using heuris- tic approach to minimize the search for selecting the switching options. Goswami and Basu [5] reported a heuristic algorithm that was based on the concept of optimum flow pattern. The optimum flow pattern with single loop formed by closing a normally open switch was found out, and this flow pattern was established in the radial network by opening a closed switch. This procedure was repeated until the minimum loss configuration was obtained. McDermott et al. [6] proposed a heuristic constructive algorithm that started with all maneuverable switches open, and at each step, the switch that resulted in the minimum increment in the objec- tive function was closed. The objective function was defined as the ratio of incremental losses to incremental load served. Lin and Chin [7] designed heuristic based switching indices, by utilizing fuzzy notations for the distribution system loss reduction. Taylor and Lubkeman [8] proposed a switch exchange type heuristic method to 0378-7796/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.epsr.2010.09.003