Study Of Comprehensive Method For Urban Distribution Network Reconfiguration And Fault Restoration With Graph-based Ant System Algorithm

Distribution network reconfiguration and fault restoration effectively optimize the operation condition of distribution network in the way of changing the status of the interconnection switches and section switches on the feeders in order to reduce the interrupted load and improve the network’s economy. Compared with the small distribution network which only contains feeders, the regional distribution network can be better optimized and more interrupted load can be restored since distribution transformers, feeders and the other lines are contained in the different voltage grades of regional distribution network. Therefore, it is necessary to study the regional distribution network reconfiguration and fault restoration.The large amount of the components in the regional distribution network leads to large feasible solution sets of reconfiguration and fault restoration. According to this characteristic, a method for solving the regional distribution network reconfiguration and fault restoration problems is proposed by using the graph-based ant system. The solving process includes an off-line stage and an on-line stage. In the off-line stage, the topological analysis is performed and the structural graph is utilized to represent the feasible solution set. The feasible solution set of fault restoration of different components can be obtained via simple transformation of the feasible solution set of the reconfiguration problem to avoid the repetitive topological analysis. In the on-line stage, the searching optimization is performed by simulating the ant colony’s traveling in the structural graph.The structural graph only relates to the topological structure of distribution network and does not relate to the load condition. Therefore, the structural graph can be built as long as the topological structure of distribution network is determined. While solving the reconfiguration and fault restoration problems, the structural graph is not needed to be built again.A new topological analysis method is proposed in this paper. In the off-line stage, the characteristic that each node in the network must be powered by a power source is used to form the reconfiguration feasible set. The feasible set does not contain any redundancy and is presented in structural graph. As the structural graph is stored in the way of chain table in computer, the searching optimization process only needs little calculation amount.Differ from the traditional methods, the results of the topological analysis method proposed in this paper contain the information of different power resources, namely the low-voltage buses of distribution transformers. Therefore, the structural graph of fault restoration can be obtained via simple transformation of the structural graph of the reconfiguration problem. As the type and amount of the fault components are different, there are two methods to modify the structural graph of the reconfiguration problem. Therefore, the topological analysis method proposed in this paper can solve the fault restoration problem under multiple fault components.The topological structures and the length of time intervals are needed to be solved simultaneously in the dynamic reconfiguration of distribution network since the coupling relationship of them is very complicated. The structural graph of dynamic reconfiguration is formed in the way of adding the structural graph that express the length of time intervals to the structural graph of static reconfiguration so that improper decoupling is avoided. As the structural graphs of topological structures in different time intervals are all same, this method avoids to analysis the topological structures repetitively. The static reconfiguration problem is hard to be solved since the big feasible solution set. According to this characteristic, a new method that reduces the searching range from the feasible set to a better set that eliminates mass of bad solutions is proposed. This method reduces the searching range in the way of changing the topological structures of two adjacent time intervals and comparing the loss of them on the premise that the amount of time intervals does not increase apparently. Therefore, the calculation amount is decreased and the calculation quality is increased.A new improved ant colony algorithm that modifies the traditional routing selection rule and phenomenon updating rule is proposed in this paper. In traditional ant colony algorithm, the parameter α is a constant and more than1. In the new algorithm, α is modified to be alterable. It changes following the exponential function while iterating. Meanwhile, the new algorithm abandons the paramete β,η and Ρ. As the result, random search mode plays a major role in the earlier stage of iteration, and emphasis search mode plays a major role in the later stage of iteration. Therefore, the new algorithm can solve the combinatorial optimization problems like regional distribution network reconfiguration and fault restoration problems.Taking an actual regional distribution network as the case, simulation results of static reconfiguration, dynamic reconfiguration and fault restoration show that using the proposed method the economy of regional distribution network can be effectively improved, meanwhile reliable fault restoration schemes can be provided.