Evaluation Theories On Modern Distribution Systems And Its Comprehensive Applications

With the advancement of both the in-depth academic research and the practical engineering applications, electric power distribution system planning has progressed into the stage characterized by informationization, routinization, practicability and fineness. A comprehensive technical evaluation with fineness is one of the fundamental tasks for planners. Several issues related to the fine evaluation on distribution systems have been proposed and studied in this thesis to meet above requirements. The main contents are as follows:(1) The theory and methodology is proposed for comprehensive evaluation of large-scale and complex power distribution systems, and the systematic indices in hierarchy are set up for the evaluation of distribution systems on safety, reliability, economy, adaptability and coordination. Some of the new indices are:"capability of anti-blackout of wide area"(which measures the N-x security criteria),"matching degree of power supply capability between high-voltage and mid-voltage distribution networks"and"load balancing"(two of which measure the coordination),"margin of network expansion"and"margin of power supply capability"(two of which measure the adaptability). With these indices, the comprehensive evaluation of high-voltage and mid-voltage distribution networks can be achieved, and the overall coordination and the load adaptability of high-voltage and mid-voltage distribution networks can be quantified effectively. The comprehensive hierarchy of above indices covers the planning, construction, operation and other links of distribution system. Meanwhile, the widely adaptable indices can be configured flexibly according the characteristics of the city and the load, at different locations and in different development stages such as the early stages of development, the rapid developing period and the developed period.(2) A systematic methodology is proposed to calculate the power supply capability of distribution system analytically, including the method based on the interconnection analysis among substations and the main transformers, respectively. Case studies on realistic distribution systems verify the following merits of this methodology: by analyzing and modeling the intrinsic power supply capability for a distribution system, this methodology can quickly identify the system's bottlenecks and weak-links in power supply, which can be a tool for fully exploiting the potential power supply capability of existing system with the aid of optimization and planning, under the conditions of limited resources(i.e. substation sites and cable channels). Besides, other four typical problems, including the parallel operation and split operation of main transformers, power supply capability of different connection modes in mid-voltage distribution networks, interconnection scales of distribution substations and the optimal transfer capability of network, are studied in this thesis. Some practical conclusions and recommendations on planning of distribution systems are given from the above research.(3) An economic analysis method is proposed for the distribution system considering the N-1 guidelines, in which the fundamental properties of power supply capability and the economic benefit are combined. The economic efficiency and the potential power supply benefit of a distribution system are thus evaluated. A complete system of economic evaluation indices is presented, including the static profitability indices and the dynamic investment benefit indices. Applications show that this method and index system can take into account both the basic characteristics of distribution system and the special features of power energy that differ from general merchandise. So they can not only evaluate the economic benefits for project investment combining with the traditional approaches of engineering economics, but can also assess the economic benefits of system-owned assets for power supplying effectively, as well as for the economy evaluation of the distribution system in operation or the planning schemes. This method can even be applied to assess the economic benefits of transmission system.To summarize, the exploring work in this thesis establishes a solid foundation for daily-frequent planning, information-based planning and elaborate planning, and has accumulated precious experience for the ongoing construction of next generation of planning information systems as well.