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김회구(Hoe-Gu Kim),이복희(Bok-Hee Lee) 대한전기학회 2017 전기학회논문지 Vol.66 No.2
This paper presents the experimental results related to soil ionization and electrical breakdown in a concentric hemispherical electrode system under lightning impulse voltages. Dynamic voltage-current and impedance-time characteristics of soil ionization were measured and analyzed. Also the electrical breakdowns of the soil gap were investigated. The time-lag to the peak current corresponds to the soil ionization propagation. The time of ionization propagation in wet sand is found to decrease with increasing the impulse currents. A drastic decrease in ground resistance was observed during the impulse current spreading in sand. The electrical breakdown appears at the wave tail of impulse voltage and results in a wide scatter in V-t curves. The voltage-current curves have a fan-like shape attributed to ionization processes which result in increasing current and decreasing voltage.
김회구(Hoe-Gu Kim),차용준(Young-Jun Cha),이복희(Bok-Hee Lee) 한국조명·전기설비학회 2017 조명·전기설비학회논문지 Vol.31 No.5
This paper presents experimental results of the effect of impulse current spreading from a ground rod installed in sand. Transient characteristics of ground rod associated with electrical discharges in soil were studied and dynamic voltage-current, resistance-time and conventional ground resistance characteristic curves were analyzed. As a consequence, a significant decrease in ground resistance was observed during the impulse current spreading in soil. The phenomenon is caused by the electrical discharges around the tip of ground rod. Time-lags to soil ionization are lengthened with increasing the current magnitude and the electrical breakdown appears at the wave tail of impulse voltage. The conventional ground resistance is exponentially decreased with impulse current. When electrical breakdown occurs in soil, on the voltage-current curves the overheating instability development appears the negative differential resistance (dU/dt〈0).
임펄스전압에 의한 토양의 이온화에 따른 접지성능의 향상
김회구(Hoe-Gu Kim),이복희(Bok-Hee Lee) 대한전기학회 2016 전기학회논문지 Vol.65 No.12
In this paper, electrical and physical characteristics associated with the ionization growth of soil under impulse voltages in a coaxial cylindrical electrode system to simulate a horizontally-buried ground electrode were experimentally investigated. The results were summarized as follows: Transient ground resistances decreased significantly by soil ionization. The voltage-current (V-I ) curves for non-ionization in soil lined up in a straight line with the nearly same slope that is the ground resistance, but they showed a ‘cross-closed loop’ of ∞-shape under ionization. The conventional ground resistance and equivalent soil resistivity were inversely proportional to the peak value of injected impulse currents. On the other hand, the equivalent ionization radius and time-lag to the maximum value of ionization radius were increased with increasing the incident impulse voltages. An analysis method for the transient ground resistances of the ground electrode based on the ionization phenomena was proposed. The proposed method can be applied to analyze the transient performances of grounding systems for lightning protection in power system installations.
임펄스전압에 의한 동심원통형 전극계에서 토양 이온화특성 분석
김회구(Hoe-Gu Kim),박건훈(Geon-Hun Park),이복희(Bok-Hee Lee) 한국조명·전기설비학회 2008 조명·전기설비학회논문지 Vol.22 No.9
본 논문은 뇌임펄스전압에 의한 토양의 이온화 현상과 모델접지시스템의 과도적 특성에 관련된 파라미터에 관한것으로 건조 모래와 습한 모래에 대한 이온화 특성을 치수가 다른 동심원통형 전극계의 실험 용기를 이용하여 연구하였다. 결과로써, 높은 임펄스전압이 인가된 모래의 비선형 전기적 특성은 이온화 과정에 의해 발생하였다. 모래의 과도임피던스는 수분의 함유량과 인가임펄스전압의 크기에 의존하며, 수분의 함유량과 인가전압의 크기의 증가에 따라 접지임피던스는 감소하였다. 본 연구결과는 뇌서지에 대하여 우수한 성능을 가지는 접지시스템의 설계에 유용한 정보가 될 것이다. This paper presents the soil ionization phenomena and the parameters with the transient characteristics of model grounding system under lightning impulse voltages. Ionization properties of dry and wet sands were investigated by using two test cells of concentric cylindrical electrode system with different dimensions. As a result, non-linear electrical behavior of sand under high impulse voltage is caused by ionization process. The transient impedance of sand depends not only on the water content but also on the magnitude of applied impulse voltages. The grounding impedance is decreased with increasing the water content and the magnitude of applied voltages. The results presented in this paper will provide useful information on the design of high performance grounding systems against lightning surge.