接地的目的主要係在保護人員及設備的安全，現行規範皆以接地電阻值來判斷接地系統的好壞，惟單靠接地電阻值並不足以明確瞭解接地安全的相關特性，還須考慮諸如地表電位、步間電壓及接觸電壓等問題。本文以電磁理論為基礎，來分析當接地棒注入故障電流時之電壓、電場及磁場變化情形，並以有限元素模擬套裝軟體COMSOL(FEMLAB)模擬分析，以改變接地棒埋設深度、或改變土壤電阻係數、或分多層不同電阻係數之土壤層、或加入接地電阻低減劑的情況下，分析比較接地電阻、地電位湧昇、步間電壓、地表電位及地表電場及磁場之變化情形，以期瞭解故障電流注入接地棒可能造成之異常電位及影響，以作為接地設計考量及接地安全的評估參考。

　　模擬結果顯示當接地棒埋設深度增加，將可大幅降低步間電壓值，且其步間電壓最大值發生處，有隨埋設深度增加而往後移趨勢；另加入低減劑確可降低接地電阻，惟應注意土壤中電流分佈改變，可能造成地表電位、步間電壓之最大值上升等現象。

　　The safety of the human beings and equipment is the main objective of grounding protection. The ground resistance is judged whether the ground system is good in existing standard, but the ground resistance is not enough to judge safety in grounding, the questions of the earth surface potential, the step voltage and the touch voltage must be considered. Based on the basis of electromagnetic theory, this thesis analyze the variation of voltage, electric field and magnetic field while the fault current flows into the ground rod. The software of Finite Element Method COMSOL (FEMLAB) is used to analyze the variation of ground resistance, ground potential rise, step voltage, earth surface potential, earth surface electric field and magnetic field when the fault current flow into the ground rod and on the conditions of ground rod buried depth changed, soil resistivity changed, the ground rod buried in different resistivities of multi-layer soil or added ground resistance reduction agent. Thus, the effect of extraordinary potential and estimate ground design and safety in grounding can be developed.

　　The simulation results show that the ground rod bury to deepen, the step voltage decreases greatly. The location of the maximum step voltage follows the changes of ground rod buried depth. The deeper the ground rod bury, the farther the maximum step voltage locates. The ground resistance reduction agent can be decrease ground resistance. Due to the changes of the current distribution in the soil, the maximum earth surface potential and the maximum step voltage may be increase.

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