| Summary: | 碩士 === 中原大學 === 電機工程學系 === 87 === The overhead power transmission system is distributed over everywhere, its ground-wires connect all the related grounding system of poles, towers, substations and plants to form an Interconnected Grounding Network (IGN). When the power system occurs ground fault on the IGN, the ground fault current will flow everywhere along the IGN and thus produce the Ground Potential Rise (GPR) on each related grounding system which may damage personnel, animals and equipments. To this problem, the conventional measures are aimed to restrict the grounding resistances of poles, towers, substations and plants under specified values. In the design of a grounding system, the affection of IGN is represented as a "current-division-factor" to conservative estimate the reducing part of ground fault current to be injected into the designed grounding system. However, this design concept has faced some difficulties such as lack of land for constructing power system and very high soil resistivity at field, these let that the low grounding resistance can not be obtained or need very large cost to attain low grounding resistance. In addition to, the ground current and potential are usually very large and distributed everywhere, if no other protective measures, the grounding system still can not protect personnel, animals and equipments from damages of ground potential even the grounding resistance had have within restricted value. To find the effective protective measures, the ground current and potential distributions of the IGN should be first analyzed, and from which the important parameters of IGN can be found out and thus derive effective protective measures. This thesis analyzes the ground current and potential distributions of the IGN considering all the possible affection parameters which include the grounding resistances of related plants, substations, towers and poles and the mutual grounding resistances between them, the self impedances of ground wires and the mutual impedances between all ground-wires and transmission lines. All the parameter characteristics are also surveyed where the important parameters can be found out. The mutual impedances between ground-wires and transmission lines will significant increase the computation time and error during the analysis of ground current and potential distributions of IGN. Thus, the thesis develops the computation algorithm based on the " decoupled method" which will largely reduce the computation time and error and attain precise analysis. Finally the IGN of a practical 69kV overhead transmission system is presented to analyze its ground current and potential distributions with respect to the variations of its important parameters. The analysis results have demonstrated the usefulness of protect analysis method and derived some available recommendations to improve the design of a grounding system.
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