| Summary: | 碩士 === 國立臺北科技大學 === 電機工程系研究所 === 97 === For the fast increasing demand of power in the city and in order to promote reliability and quality of power system, it is a trend to build EHV substations in the area of load center. However, due to the difficulty of obtaining right-of-way and the local residents protest, it is unavoidable to build indoor substations as underground type or layered type. There are various electrical equipments install on different floors in the underground Extra High Voltage (EHV) substation and to form a cubic structure, however, the area is too limited to construct large grounding grid, the method for that is to widely install grounding buses and grounding conductors to form the grounding grid for each floor, and its grounding performance will depend on the grounding buses, grounding conductors and the characteristics of ground gird. Due to the large short circuit capacity of EHV substation, the large amount of fault current will inject into substation ground grid during ground fault, and that will damage the personnel and equipments in the substation.
This thesis aims are to study the various electromagnetic characteristics of ground system of main grounding grid and grounding grid of each floor during ground fault, which including ground potential rise (GPR), step voltage, touch voltage, and the distribution of electromagnetic field. Based on the analysis results, the influences of ground fault on the personnel, equipment and other system are assessed. The circuit model for analyzing the ground faults with respect to different fault locations are first constructed by the alternative transient program (ATP), from which we can obtain the fault currents and the injection current to ground grid of each floors at fault points, natural point of main transformers, grounding points of cable shielding conductors. Furthermore, the electromagnetic characteristics of grounding system at transient states and steady states are analyzed by the software namely CDEGS (Current Distribution Electromagnetic Grounding and Soil Structure Analysis). Finally, based on the results, the affections of electromagnetic characteristics of grounding system on personnel, equipments and other systems are assessed. The study results can be used for further studied the protection measures in the underground EHV substation.
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