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.
An Evaluation Method for Power Supply Capability of Distribution System Based on Analyzing Interconnections of Main Transformers
To improve insufficiency of traditional method based on the load supply capacity referring to the transmission system planning,this paper proposed a straightforward method to evaluate the power supply capability of distribution network,which is based on the interconnections among main trans-formers considering the N?1 guideline. Firstly,a series of interconnection schemes will be drawn from the connection analysis of distribution system. Secondly,the maximum load rate of each main transformer can be got by analyzing each interconnection schemes according to the N?1 guideline. Finally,based on a comprehensive analysis of the above results,the maximum permissible load rate of each main transformer can be obtained,and then the power supply capability of the entire distribution system can be calculated. Through the application of this method in a district of Shanghai,China,the effectiveness and the accuracy of the method are demonstrated. In summary,the method proposed in this paper based on the N?1 guideline and the interconnections among main transformers is a simple and practical tool to evaluate the power capability of a distribution system;besides,the interconnection bottlenecks of the distribution system and the load transferring bottlenecks can be identified easily by the method,thus providing effective references for urban distribution network planning.
A practical GIS-based decision-making support system for urban distribution network expansion planning
The computer-supported decision-making system has become an essential tool for the sustainable growth and expansion planning of modern urban power distribution network. Current packages with planning functions are independent packages, which are limited in the academic research. Presently, in Shanghai Municipal Electric Power Company and its subordinate units, a geographic information system(GIS)-based production management system(PMS) has been applied successfully as the working platform in most departments, which makes the further research on the computer-aided decision-making system possible and feasible. Taking the PMS as the graphics supporting platform, this paper studies and develops a practical GIS-based decision-making support system for urban distribution network expansion planning, which establishes a primary foundation for information-based planning, daily-frequent planning and elaborate planning. Firstly, the physical structure of the system is designed with a four-layer hierarchical architecture, including the data layer, platform layer, application layer and performance layer, which is suitable for object-oriented development to ensure the security and stability of the system. Secondly, to satisfy the requirements of distribution expansion planning, the main functions of the system are divided into seven modules according to the planning process abstracted in the computer, including the module of current situation analysis, load forecasting, substation locating and sizing, network planning, cable channel planning, economic evaluation of planning and so on. There is at least one or one set of practical mathematical models and methods for planning adopted in each module to ensure the accuracy and reasonableness of the final planning results. Finally, an actual planning of Shanghai, China is accomplished with the expansion planning system. The practical application achievements show that the system can not only optimize the expansion planning results of urban power distribution network, but also reduce the workload of computation, analysis and graphics drawing dramatically.