Power Distribution System Reliability Assessment

As the connection of the whole power system and load points, power distribution system play an important role in the modern society by supplying electric power for customers. For the proceeding of generating electric power, providing electric power and consuming electric power at the same time, it is inevitable to interrupt the power supplying for customers , which is resulting from fault or maintance of distribution system elements. Distribution system indices reflect the structure and operation characteristics of all power system. The research and application of distribution system reliability is important means to warrant the electric power quality, and also play an important role to promote the techniques and control level of electric utility industry, to upgrade the economic performance and society benefits, and to direct the design, operation and extention of distribution networks.Distribution system reliability evaluation is an important tache in the power system reliability evaluation. There are some own features in distribution system reliability evaluation. Based on the profound analysis of distribution system, this paper indetailes the reliability models of elements, element reliability indices and system reliability indices, which provide the convenience to the following reliability evaluation.Since the radial distribution system is made up of many components and has complex structure and various operation modes, it is very difficult to assessment its reliability. The paper, according to the features of radial distribution system with complex sub-feeders, firstly presents a reliability assessment algorithm for radial distribution system based on fault pervasion of multilevel B-C-N-M region sub-networks. In this algorithm, distribution network is divided into several multilevel B-C-N-M region sub-networks according to the locations of circuit breakers and section switches. The equivalent reliability parameters of sub-networks are calculated by equivalent means. The load point reliability indices and system reliability indices are computed based on the failure pervasion of every sub-network. The contribution of reserve supply, circuit breakers, fuse and section switches on the reliability indices, is taken into account. This method has little computation burden, and can be used for reliability evaluation of any complex radial distribution system.On the foundation of the method of deviding radial distribution network into severa sub-networks and the weakness of sub-network pervasion method , the paper models the states transition of power distribution system according to the dynamic traits of operable components such as breakers, disconnect switches and alternative supply switches. Due to the limit of the operable component number, the number of states in this model is relatively small. Based on this model, all static components are partitioned into different kinds through the first time classification and then secondary classification. System states transition under failure is only simulated one time for any kind of components, while the corresponding states'failure rates and failure duration time are calculated. Then every load point's indices are got through simple time takes advantage of making operation and superpose operation.The presented model and algorithm for distribution system reliability evaluation have the simple structure and little calculating redundancy, and have been programmed to evaluate the reliability of the IEEE RBTS Bus 6. The calculating output proved the validity and feasibility of the presented models and algorithms.