Studies On Distribution System Reliability Assessment Method And Application

Distribution system, linking transmission system and users together, distributes and supplies electricity to users. It includes distribution substation, high and low voltage distribution lines, feeder lines and other networks as well as devices. As a part connected directly to users, the reliability of distribution system directly affects the normal power users. Therefore, it plays an important role in the safety, reliability and economy of power supply. With the restructuring of economy and growing proportion of demanding industries such as information industry, security requirement of users becomes higher and higher. How to supply users with high-safety electricity is an unavoidable reality of electricity workers, and a necessary requirement for the development of power systems.The power supply reliability of low-voltage users is one of the main indexes that reflect the ability and quality of power supply utilities. It embodies the comprehensive level of power system in terms of plan, design, device selection, construction, production, operation and service. However, it is difficult to get the statistic reliability of low-voltage users, because such users are numerous and widely distributed, which means the basic data is too large and operating data is hard to collect. Therefore, exploring an investable method that can calculate the statistical reliability of low-voltage users and provide the basis for evaluation of the entire distribution system reliability and economy has important theoretical significance and value.Comparing to generation and transmission system, the study of distribution system reliability started late. Due to lack of necessary statistical data and effectively analytical method, development was relatively slow. In recent years, with the rapid development of the national economy, the urban power load has been increasing quickly so that the conflict between supply and demand has become very prominent. Consequently, the reliability of power distribution has been becoming more and more significant in producing management. In order to achieve maximum benefit based on limited resource, we urgently need a kind of scientific and rational plan of distribution system, which will contribute to the development of reliability assessment of distribution system.Most power transmission and transforming equipments are exposed to external environment. In addition, the main equipments are susceptible to weather events, which is an important feature of power system. Atmospheric humidity, pollution level, strong wind, snow as well as ice rain, thunderstorms, fog and other occasional weather events will affect the fault rate of components; severe weather events may even lead to a cluster of failures, seriously affecting the level of system reliability. Studying the method that can simulate the effect of strong wind and other climatic conditions on the reliability of high-voltage distribution system will contribute to a better understanding of faults aggregation under extreme weather conditions, and then it becomes possible to reveal the role of climate from a micro, fine-grained level, which has theoretical significance.Focusing on assessment method of low-voltage power system reliability, new evaluation method of system as well as distribution network reliability, and assessment of high-voltage distribution system reliability considering the effect of strong wind, this dissertation studies the reliability of power distribution in detail, mainly including:(1) Reliability assessment method and application of low-voltage power supply systemsA statistical evaluation scheme of power supply reliability of low-voltage users based on a test of probabilistic and statistical model is proposed, and relative software is developed and applied to actual power system. According to the calculation as well as analysis results of probabilistic and statistical theory, and precision requirements within the statistical range, corresponding reliability monitoring points of low-voltage users are set. Then operating data collected from monitoring points are transferred to a computer center, which calculates and analyzes indexes automatically. This scheme effectively overcomes the problem that the investment of reliability statistics of low-voltage users in China and the problem that statistics results have big errors.(2) Reliability assessment method of distribution system based on success probabilityHow to improve the distribution network reliability and minimize the investment is an important topic in modern power system operation and control. With reviewing some general used reliability assessment methods of distribution system, by introducing the concept of average success operating probability of component, a new method is proposed based on success probability. The method will not become more complex with the number of branch feeder lines increasing. Therefore, based on the network topology analysis, only one traversal is required, and then the fault rate as well as success operating probability of a load point can be obtained. Further, the fault duration can be determined. This method has several advantages. The failure rate and success operating probability can be calculated in parallel; the network model will not become more complex when the number of branch feeder lines increases; the reliability index can be obtained quickly and accurately by simple calculations such as addition and multiplication; it has clear principles, accurate results, fast computation and can be programmed easily. (3) Reliability assessment of high-voltage distribution network considering windy climateThe principle and research status of the effect of climate on distribution network reliability are analyzed. According to the features of the impact of windy climate on the grid, a numerical simulation method of the effect of windy climate on power system is proposed. It generates random failure scenarios by Monte-carlo simulation method, carries out analysis and calculation through a detailed time-domain simulation tool. The proposed method can simulate the characteristics of fault aggregation under windy climate, which makes up the shortcoming caused by analyzing only from the steady-state view. A reliability evaluation system for high-voltage distribution system considering the windy climate is developed. Based on the actual data of Shandong power grid, a large number of simulations and reliability analysises have been done under the condition of a given external wind. Example simulations show that the system can handle actual grid data. A large number of analog sampling simulations can reveal potential problems, and provide the reliability level of system under the condition of fault aggregation.