Reliability Evaluation For Distribution System With Distributed Generation

In the past, as the last link of the power transmission, the importance of distribution network tends to be ignored. With the development of people’s living standards, the increasingly strong demand for electricity puts forward higher requirements for the reliability of power supply. As a distribution terminal connected to the customers, the reliability of distribution network directly reflects the level of service of the electricity sectors. Today, reliability has become one of indispensable system planning.The methods of reliability analysis mainly are analytical method and simulation method. The model of analytical method is accurate and caculate quickly, but there are some shortages, such as it unable to get the range of indices of reliability and cannot distinguish which customers are effected by the outage. It also too complex for those distribution systems with many branches.The simulation method can be detailed simulate failure process of elements, so we can get more comprehensive indices of the load point and system. Because of the insensitivity of the complexity of its system, the simulation method have been gotten more widely used.Distribution networks are generally closed-loop design and open-loop operation, and the network generally alongs the electricity load density region, mostly radial. Due to multiple load points usually connect to the same line, they often have the same outage region. Based on this, combined with the minimal path method and section algorithm, this paper use Monte Carlo simulation to carry out the distribution network reliability analysis. The method directly one-way search against the direction of power flow from load point for the minimal path, eliminating the trouble of traversal search. Using section algorithm, this method takes the traditional elements of non-minimal path into consideration to avoid the equivalent problem. Finally, an example illustrates the correctness,speediness and validity of the method.Because fault partitioning has a direct relationship with the state of the operating elements, In this paper, the minimal path method based on the operating elements is used to make the search process more simple and efficient. The preparation of the C language program and using of the operating elements "truth table" to divide the load point outage type makes it much simpler than previous method to the judgment of the outage type. The biggest feature of this method is to not have any equivalent to the system structure, and it directly input elements’parameters based on the single line diagram of the power distribution network and set the number of simulation years to come to the reliability indices of load points and system. As the Monte Carlo simulation is insensitive to the number of network elements, it is particularly suitable for those system with complex branch feeders.DG access to the grid bring a series of problems, reliability problem is one of them. The planning authorities have to consider how the DG plays an role in the distribution system reliability. Because of the highly uncertainty of DG’s output, the traditional analytical method is difficult to caculate, but simulation method can be very good at deal with this problem. Based on the operating elements and the minimal path method at the introduction of DG’s random model, this artical uses Monte Carlo simulation to simulate the indices of each load points and system reliability.The economic analysis shows that the DG’s access can bring good economic benefits to customers while improve reliability.