1. Introduction During the last ten years, irregular residential buildings have been widely established in some agricultural fields located in centers of Iraqi cities. These buildings have been supplied by electricity from the nearest electrical distribution feeders without previous planning since such buildings do not exist in future planning developed by General Directorate of Urban Planning in Iraq. As a result, most of the feeder lines supplied the mentioned buildings suffer from overloading and poor voltage profile which causes malfunction in the operation of customer electrical devices (Kjolle et.al., 2008). Moreover, the power losses are also increased in some parts of these feeders due to the presence of insufficient cables sizes for the load current. In order to solve this problem, several strategies have been proposed by electric power distribution utilities in Iraq to enhance the power distribution system. The most utilized strategies are listed below: ? Upgrade the cable size of the overloaded feeder lines. ? Installation of shunt capacitors along the distribution feeder to compensate the load inductive power.
Journal of Babylon Univ ersity/Engineering Sciences/ No.(5)/ Vol.(25): 2017
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However, these strategies are very expensive and are not applicable in this time due to Iraqi economic crisis. Therefore, it is very important to develop an alternative strategy to decrease the power losses and improve the voltage profile with less cost. The proposed strategy presented, in this paper, is the reconfiguration of distribution feeders (RDF). The main idea of RDF strategy is based on changing the topological structure of distribution feeder by altering the status of open/close switches to achieve minimum power losses and acceptable voltage profile. The main advantage of the proposed strategy is represented by the low investment requirement since it uses the switches which are already available in the distribution systems. Although this strategy is very attractive, it requires an accurate optimization method to obtain the optimal configuration structure of the system. In addition, it requires an optimization method with selective search space to search among only the available system switches (Aman et.al., 2016). Many RDF methods have been developed using different optimization methods, such as simulated annealing (Su et.al., 2001), genetic algorithm (Taher et.al., 2014), bee colony (Ganesh, 2014), immune systems (Alonso et.al., 2015), Ant colony (Tolabi et.al., 2015), Particle swarm (Balakrishna et.al., 2014), evolutionary programming (Aman et.al., 2013). However, most of these methods were tested using simple and theoretical radial networks. Water cycle optimization method (WCOM) (Eskandar et.al., 2012; Sadollah et.al., 2015), which is based on water cycle phenomenon, is recently developed. During the previous two years, WCOM shows superior performances compared to other optimization methods for different applications (Jahan et.al., 2015; Khodabakhshian et.al., 2016; Heidari et.al., 2017). However, WCOM was formulated for continuous or discrete optimization problems using free search space which is not applicable to RDF problem.
In this paper, optimal reconfiguration of distribution systems is proposed to enhance the performance of Iraqi power distribution systems. The optimal radial configuration is determined using selective water cycle optimization method which is also proposed, in this paper to consider the selective search space required in the reconfiguration problem. The objective of proposed system reconfiguration method is to minimize the power losses and then improve the voltage profile with considering the current-carrying capacity of the system branches. An actual distribution system selected from Hillah city network is used, in this paper, to test and verify the effectiveness of the proposed methods. Superiority of the proposed methods compared with other methods is also verified.
2. Proposed Distribution System Reconfiguration Method
In Iraq, the distribution systems are constructed as weakly meshed, but are operated with radial configuration using the switches located in the end of each branch. Two types of switches are available in the systems, which are normally closed switches (sectionalized switches) and normally open switches (tie switches). By changing the state of these switches, different radial configurations can be obtained. The main purpose of the mentioned switches design is to manage the system configuration at contingency and fault conditions.
In this paper, an optimal reconfiguration method is proposed for Iraqi power distribution systems to minimize the active power losses and then improve the voltage profile with considering the current-carrying capacity of the system branches. The