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보조전극의 수직배치를 통한 접지저항 측정의 타당성 연구
김유하(You-ha Kim),이복희(Bok-Hee Lee) 한국조명·전기설비학회 2011 한국조명·전기설비학회 학술대회논문집 Vol.2011 No.11
The fall of potential method is typically used for measuring the ground resistance of large-sized grounding system. Because the distances between the test ground grid and auxiliary electrodes are limited in downtown areas, it is very difficult to measure acurately the ground resistance of large-sized ground system. Therefore the method of measuring the ground resistance using the vertically-placed auxiliary electrodes was investigated. Various simulations and trial tests were carried out in two-layer earth structure, and the validity of the method of measuring the ground resistance was examined.
보호거리와 부하 유형에 따른 SPD의 보호효과에 대한 실험적 고찰
이복희(Bok-Hee Lee),김유하(You-Ha Kim),안창환(Chang-Hwan Ahn) 한국조명·전기설비학회 2012 조명·전기설비학회논문지 Vol.26 No.10
Surge protective devices(SPDs) are widely used as a most effective means protecting the electrical and electronic equipment against overvoltages such as lightning and switching surges. When installing SPDs, it is essential that the voltage protection level provided by SPDs should be lower than the withstand voltage of the equipment being protected. But even the proper selection of SPDs are achieved, the voltage at the equipment terminal may be higher than the residual voltage of SPD due to the reflection and oscillation phenomena. This paper was focused on the investigations of the conditions for which the equipment is protected by an SPD taking into account the influences of the protective distance and type of load. The protective effects of SPD with voltage-limiting component were analyzed as functions of types of load and protective distance between the SPD and load. As a result, in the cases of long protective distances, capacitive loads and loads with high resistance, the voltage at the load terminal was significantly higher than the residual voltage of SPD. It was found that the proper installation of SPDs should be carried out by taking into account the protective distance and type of load to achieve reliable protection of electronic equipments against surges.
보호거리에 따른 전압제한형 SPD의 보호효과에 대한 시뮬레이션기법
이복희(Bok-Hee Lee),김유하(You-Ha Kim),안창환(Chang-Hwan Ahn) 한국조명·전기설비학회 2013 조명·전기설비학회논문지 Vol.27 No.7
This paper presents a method of simulating the protection effects of surge protective devices(SPDs) depending on the protective distance and types of input impedance of load to be protected. In order to analyze the protective performances of voltage-limiting type SPDs associated with the reflection and oscillation phenomena, the terminal voltage across load being protected and the residual voltage of SPDs were simulated by using EMTP model as functions of the protective distance and types of input impedance of loads. As a consequence, SPDs should be installed by taking into account the protective distance and input impedance of loads to achieve reliable protection of electrical and electronic equipment from lightning and switching surges. It is expected that the simulation method proposed in this paper could be practically used in design for installing SPDs in low-voltage distribution systems.
전류 및 전위 보조전극을 수직으로 배치하는 전위강하법을 이용한 접지저항의 측정
이복희(Bok-Hee Lee),김기복(Ki-Bok Kim),김유하(You-Ha Kim) 한국조명·전기설비학회 2012 조명·전기설비학회논문지 Vol.26 No.3
The fall-of-potential method is commonly used in measuring the ground resistance of large-scaled grounding system and the current and potential auxiliary electrodes are horizontally arranged. Because the distances between the ground grid to be tested and auxiliary electrodes are limited in downtown areas, it is very difficult to measure accurately the ground resistance of large-scaled grounding system. In this paper, the fall-of-potential method of measuring the ground resistance with the vertically-placed current and potential auxiliary electrodes was examined and discussed. The validity and good accuracy of the proposed method of measuring the ground resistance were confirmed through various simulations and actual tests carried out in uniform and two-layer soil structures.
유양우(Yang-Woo Yoo),김승민(Seung-Min Kim),김유하(You-Ha Kim),이복희(Bok-Hee Lee) 한국조명·전기설비학회 2014 조명·전기설비학회논문지 Vol.28 No.10
This paper presents the results of model tests for the attachment process of lightning leader to ground which is one of poorly understood processes of cloud-to-ground lightning discharges. In order to simulate the attachment process of lightning leader to ground, we investigated the discharge characteristics of air gap between the tip of needle-shaped electrode and the soil surface as a parameter of moisture content in soils when the positive and negative 1.2/50㎲ lightning impulse voltages are applied. The breakdown voltage and the discharge light were observed. As a result, the attachment processes of lightning leader to ground are strongly dependent on the grain size and the moisture content of soils. The time to breakdown was shortened with increasing the magnitude of incident impulse voltages. The delay time from application of the highest voltage to breakdown in sand is shortened with increasing the moisture content. The delay time from application of the voltage to breakdown in gravel varied from about 0.5㎲ to several ㎲. As the moisture content in soil increases, the breakdown voltages are decreased and the breakdown voltage versus time to breakdown curves are shifted toward the lower side. The results obtained in this work are similar to those for non-uniform air gap stressed by lightning impulse voltages.