Interval Algorithm Of Bayesian Network For Evaluating The Reliability Of Electrical Distribution Networks With Multi-load Levels

The EDN is an important part of the electrical power system. The research results show that 80% of the total customer interruptions results from EDNs. At present, along with the EDNs'development, more and more research are focused on evaluating the reliability of EDNs, so as to transmit the electricity to the customers with high quality and economical efficiency. In this paper, the technique of EDNs reliability evaluation has been integrated with theories of the Bayesian network, interval numbers and power system analyzing and planning, and main results are as follows:â‘ A reliability evaluation algorithm for EDNs using the Bayesian network is implemented. A four-layer Bayesian network for EDNs, which consists of the component layer, the section layer, the load point layer and the system layer, is modeled using the section technique. The relationship between the component and section layers is established using the section technique and the equivalent network. The node types of load points are determined using an analytical method for enumerating the faults of the branch sections and switching devices. The reliability of load points are evaluated using the relationship between the section and load point layers and the matrix store technique. The system reliability of an EDN is evaluated based on the relationship between the load point and system layers. Using the bi-directional reasoning function of the Bayesian network, the weak parts of load points are identified by the reliability parameters of components, and the weak parts of an EDN are identified by the system reliability index of Energy Not Supplied.â‘¡An interval algorithm for evaluating the reliability of EDNs using the Bayesian network is implemented. This algorithm, integrated with theory and operation rules of interval numbers, has considered the uncertainty of the components'reliability parameters, and results show reliability indices of both best and worst situation.â‘¢Due to load transferring, the lines of an EDN might be overloaded, and the voltage of nodes might be out-of-limit. A reliability evaluation algorithm for EDNs considering constraint of power flow is designed. Based on the characteristic of the structure and power flow of EDNs, voltage of nodes are estimated using an equivalent-load-moment model, according to the results, a section load shedding strategy is generated. This algorithm can reduce calculation complexity a lot.â‘£The cluster technique is used to create a multi-level model of the annual load curve, and the annual reliability indices can be obtained by weighting the indices for each load level by its probability. Case studies show the effect of the number of load levels on calculation accuracy and speed.A program is developed by MATLAB 7.8.0, which contains all the functions disscussed above, such as power flow estimation, reliability evalutaion, weak parts identification and load curve clustering. Case studies of the RBTS-BUS2 EDN, IEEE-33-nodes network and a 527 nodes system are analyzed, and the results show that the proposed algorithm has the validity and high efficiency.