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Analysis of Transient Ground Impedances Based on Soil Ionization under Impulse Voltage
Kim, Hoe-Gu,Lee, Bok-Hee The Korean Institute of IIIuminating and Electrica 2016 조명·전기설비학회논문지 Vol.30 No.8
In this paper, the behavior of transient ground impedances in a coaxial cylindrical electrode system stressed by impulse voltages were experimentally investigated. The ground impedance-time characteristics and the voltage-current behavior for 4 types of soils were analyzed and discussed. Also, this paper modeled the electrode system into two-dimensional axial symmetry and analyzed the soil ionization growth and electric field distribution in the vicinity of the surface of the ground electrode. As a result, the ground impedance-time (Z-t) curves are dependent on the types of soils. The voltage-current (V-I) curves for all sample soils show a 'cross-closed loop' of ${\infty}$-shape under ionization. When an impulse voltage is applied to the ground electrode buried in the ground, the electric field intensity around the ground electrode changes over time. It is known that transient ground impedance is dependent on the time-varying soil ionization in the vicinity of the surface of a ground electrode.
Analysis of Transient Ground Impedances Based on Soil Ionization under Impulse Voltage
Hoe-Gu Kim,Bok-Hee Lee 한국조명·전기설비학회 2016 조명·전기설비학회논문지 Vol.30 No.8
In this paper, the behavior of transient ground impedances in a coaxial cylindrical electrode system stressed by impulse voltages were experimentally investigated. The ground impedance-time characteristics and the voltage-current behavior for 4 types of soils were analyzed and discussed. Also, this paper modeled the electrode system into two-dimensional axial symmetry and analyzed the soil ionization growth and electric field distribution in the vicinity of the surface of the ground electrode. As a result, the ground impedance-time (Z-t) curves are dependent on the types of soils. The voltage-current (V-I ) curves for all sample soils show a ‘cross-closed loop’ of ∞-shape under ionization. When an impulse voltage is applied to the ground electrode buried in the ground, the electric field intensity around the ground electrode changes over time. It is known that transient ground impedance is dependent on the time-varying soil ionization in the vicinity of the surface of a ground electrode.
( Dae Hoe Gu ),( Moon Young Kim ),( Yeon Seok Seo ),( Sang Gyune Kim ),( Han Ah Lee ),( Tae Hyung Kim ),( Young Kul Jung ),( Altay Kandemir ),( Ji Hoon Kim ),( Hyunggin An ),( Hyung Joon Yim ),( Jong 대한간학회 2018 Clinical and Molecular Hepatology(대한간학회지) Vol.24 No.3
Background/Aims: The most widely used method for diagnosing sarcopenia is the skeletal muscle index (SMI). Several studies have suggested that psoas muscle thickness per height (PMTH) is also effective for detecting sarcopenia and predicting prognosis in patients with cirrhosis. The aim of this study was to evaluate the optimal cutoff values of PMTH for detecting sarcopenia in cirrhotic patients. Methods: All cirrhotic patients who underwent abdominal computed tomography (CT) scan including L3 and umbilical levels for measuring SMI and transverse psoas muscle thickness, respectively, were included. Two definitions of sarcopenia were used: (1) sex-specific cutoffs of SMI (≤52.4 ㎠/㎡ in men and ≤38.5 ㎠/㎡ in women) for SMIsarcopenia and (2) cutoff of PMTH (<16.8 mm/m) for PMTH-sarcopenia. Results: Six hundred fifty-three patients were included. The average age was 53.6±10.2 years, and 499 patients (76.4%) were men. PMTH correlated well with SMI in both men and women (P<0.001). Two hundred forty-one (36.9%) patients met the criteria for SMI-sarcopenia. The best PMTH cutoff values for predicting SMI-sarcopenia were 17.3 mm/m in men and 10.4 mm/m in women, and these were defined as sex-specific cutoffs of PMTH (SsPMTH). The previously published cutoff of PMTH was defined as sex-nonspecific cutoff of PMTH (SnPMTH). Two hundred thirty (35.2%) patients were diagnosed with SsPMTH-sarcopenia, and 280 (44.4%) patients were diagnosed with SnPMTH-sarcopenia. On a multivariate Cox regression analysis, SsPMTH-sarcopenia (hazard ratio [HR], 1.944; 95% confidence interval [CI], 1.144-3.304; P=0.014) was significantly associated with mortality, while SnPMTH-sarcopenia was not (HR, 1.446; 95% CI, 0.861-2.431; P=0.164). Conclusions: PMTH was well correlated with SMI in cirrhotic patients. SsPMTH-sarcopenia was an independent predictor of mortality in these patients and more accurately predicted mortality compared to SnPMTH-sarcopenia. (Clin Mol Hepatol 2018;24:319-330)
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.