An Improved Model of Total Supply Capability for Distribution Systems
The Total Supply Capability (TSC) model is newly proposed to evaluate the maximum load a distribution system can supply under the N-1 security guideline. This TSC model and a linear programming algorithm can calculate the accurate TSC of a distribution system; but the results of transformer loading rates calculated by this model are usually unbalanced, which is unacceptable in the practical operation. In order to solve this problem, this paper discusses the solution properties of the TSC model first. It is found that the transformer loading rates vector is not unique under the same TSC level; and only one of the optimal solution can be obtained from the linear programming software such as lingo. Then, an improved TSC model is proposed, which takes variance of loading rates and heavy-load areas into account. This new model is divided into two parts, the first part is the TSC calculation process, and the second part is the most balanced loading rate calculation process. Finally, a practical case is given to illustrate the effect of the improved model. It has shown that the loading rates calculated through this method are more balanced than the original one under the same TSC. The method can be useful tools to help system planners to get the best configuration of transformers in distribution systems.
Rapid evaluation method for power supply capability of urban distribution system based on N − 1 contingency analysis of main-transformers
Abstract A proper evaluation on the power supply capability of urban distribution system is of much social and economical significance. In competitive marketing environment, to satisfy the sustainable growth of distribution loads, electric utilities must judge whether the return of power supply capability is sustainable and valued against the certain amount of investment. Therefore, to make up the insufficiency of traditional methods referring from the concept of total transfer capability (TTC) of transmission system, this paper proposes a straightforward method to evaluate the power supply capability (PSC) of distribution system, which is based on N  − 1 contingency analysis of interconnected main-transformers. Firstly, a series of interconnected main-transformer groups are drawn from the main-transformers’ interconnection analysis after the topological simplification of distribution system. Secondly, the maximum average loadability of each main-transformer is concluded through the N  − 1 contingency analysis of every interconnected group. Finally, based on a comprehensive analysis of all the interconnected groups’ results, the maximum permissible loadability of each main-transformer can be obtained, thus the PSC of the entire distribution system can be calculated. Through the application in a distribution system of Shanghai, China, the effectiveness and the accuracy of the method are demonstrated. The application results suggest that, the method presented in this paper is a simple and practical tool to evaluate the PSC of a distribution system, which needs only one calculation with constraints according to the N  − 1 guideline. Moreover, the interconnection weak-points and the interconnection bottlenecks of the distribution system can be identified easily with this approach, thus providing effective references for urban distribution network planning and the following project investment decisions.
Overall evaluation of the supply capability in distribution networks based on fuzzy method
Combined with the actual situation of 10 kV distribution network of electric power supplier in Beijing city, based on collecting amount of statistic information, this paper calculate and analyze the operation status of the distribution grid. Set up subjection function and evaluate modeling from the rate of load, loss and the N-1 check of the voltage level of grid node aspects, and get the subjection value and ldquogoodrdquo or ldquobadrdquo expectation in fussy method. These results are rational evaluation for the supply capability of the medium voltage distribution grid in the city. Considering all kinds of factors, present the comprehensive and quantitative evaluation index of the electric network was got through setting up appraise index collection, matrix of judgment level collection and suited operators. The evaluation index provides basis for the construction of the network structure programming, and costing program of distribution.