| Summary: | 碩士 === 國立臺北科技大學 === 電機工程系研究所 === 101 === The typical high voltage (HV) (22.8kV and 11.4kV) utility power supply system (UPSS) in each science park is fed by three-phase four-wire underground cables. The main grounding problem is that the neutral conductors of underground feeder cables are not drawn into customer substations, which lead to detrimental effects on ground fault protection and ground potential rise (GPR) of customer substation. In addition, transfer voltage to customer substation due to ground fault at utility substation is severe, especially supplied by extra high voltage substation (E/S). Moreover, those customers near utility substation are subject to very high lightning and switching surges from utility substations. Obviously, to mitigate these problems, the grounding of both customer substation and UPSS should be improved together. In thesis, we use alternative transient program (ATP) to construct the HV UPSS model and then simulate the characteristics of ground fault, lighting surge and switching surge to get the data of fault current that injected into customer grounding system. Furthermore, we use these data to analyze the electromagnetic chacacteristic of grid of customers by a software package namely the current distribution electromagnetic ground and soil structure analysis (CDEGS) program. The analysis result ensure that the original ground system is highly risky. Obviously, to mitigate these problems, the grounding of both customer substation and UPSS should be improved together. The grounding improved measures include not only reducing ground resistance but also the use of related supporting measures and their integration which produce more effective results. This thesis aim to find all the feasible supporting measures of grounding base on simulated annealing method, the variables include the measures used in customer substation and that of used on UPSS. The costs of the measures will be assessed and optimal integration based of them are implemented to satisfy all the grounding requirements and constraints by lowest total cost. Thereby, all the touch voltage, step voltage and metal-to-metal touch voltage at customer substation will be confined within safe range to assure the personnel safety when ground fault, lightning and switching surges; and the transfer voltage, GPR and magnetic field are all under the limits for protecting equipments from over voltage and magnetic interference. Moreover, the total cost for grounding integration will be minimized, thus this research will upgrade the electric supply safety in science park and conform with economy.
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