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이복희(Bok-Hee Lee),엄상현(Sang-Hyun Um),김유하(You-Ha Kim),이강수(Kang-Soo Lee),전병욱(Byung-Wook Jeon),최종혁(Jong-Hyuk Choi) 한국조명·전기설비학회 2013 조명·전기설비학회논문지 Vol.27 No.3
This paper deals with the frequency-dependent ground impedance of ground grids combined with the carbon ground electrodes. Ground grids are generally valid for multipurpose grounding systems as well as lightning protection systems. The carbon ground electrodes may be supplementarily used to reduce the high frequency ground impedance and to improve the transient response to surge currents. The frequency-dependent ground impedances of ground grids combined with or without the carbon ground electrodes were measured and their simulations with due regard to frequency-dependent soil resistivity were implemented by using EMTP program and Matlab modeling. As a consequence, the ground impedance of ground grids combined with the carbon ground electrodes is significantly reduced when the test current is injected at the terminal of the carbon ground electrode. The measured and simulated data for the test ground grids fairly agree with each other. It was found that the proposed method of simulating the frequency-dependent ground impedance is distinguished. The simulation techniques of predicting accurately the ground impedances without actual measurements can be used in the design of grounding systems based on ground grids and the carbon ground electrodes.
종속 접속된 전압제한형 SPD의 직격뢰 서지전류에 대한 에너지협조
이복희(Bok-Hee Lee),엄상현(Sang-Hyun Um) 한국조명·전기설비학회 2014 조명·전기설비학회논문지 Vol.28 No.5
Cascaded applications of surge protective devices(SPDs) are required in order to reduce the stress on the electrical and electronics equipment being protected, and the energy coordination between the cascaded SPDs is very important. This paper deals with the experimental results obtained from the installation conditions of full-scale SPDs. The energy coordination between the upstream Class I SPD and the downstream Class II SPD was measured using a 10/350μs impulse current due to direct lightning flashes. The distances between the cascaded SPDs were 3, 10, and 50m, and the maximum test current was 12.5kA. As a result, the energy sharing between cascaded SPDs was dependent on the voltage protection level of each SPD and the distance between two SPDs. An overview of how to select SPD ratings in applications of cascaded SPDs system was discussed based on the energy coordination between the two SPDs. The proposed test results for the energy coordination between two-stage cascaded SPDs can be used in effective applications of SPDs.
정형외과 수술 후 발생한 섬망의 발생 빈도와 관련 인자
이시욱(Si-Wook Lee),조철현(Chul-Hyun Cho),배기철(Ki-Cheor Bae),이경재(Kyung-Jae Lee),손은석(Eun-Seok Son),엄상현(Sang-Hyun Um) 대한정형외과학회 2019 대한정형외과학회지 Vol.54 No.2
목적: 정형외과 수술 후 환자의 섬망 발생 빈도 및 섬망에 미치는 영향 인자를 분석하고자 하였다. 대상 및 방법: 1년간 단일 상급 종합병원에서 정형외과 수술을 시행 받은 성인 환자 2,122예를 대상으로 하였다. 이들 중 정신건강의학과 협의 진료하에 Diagnostic and Statistical Manual of Mental Disorders-V 진단 기준에 부합하며 섬망 관련 투약력이 확인된 환자 132예를 선별하였고 수술 원인 및 수술 부위에 따른 섬망 발생률의 차이와 입원 후 섬망 발생까지의 시간 및 지속 시간에 영향을 미치는 인자를 분석하였다. 결과: 전체 수술 환자 중 6.2% (132/2,122예)에서 섬망이 발생하였다. 섬망 환자군의 평균 나이는 77.4세(범위, 54-92세)로 비섬망 환자군의 평균 나이(58.1세)보다 많았고, 섬망 환자군의 여성 비율이 63.6% (84/132예)로 비섬망 환자군의 여성 비율(49.0%)보다 높았다. 외상에 의한 수술 후 9.3% (85/916예), 질환에 의한 수술 후 3.9% (47/1,206예)의 섬망 발생률을 보였다. 수술 부위별 섬망 증상의 발생률은 두 부위 이상 수술을 시행한 경우 29.2% (7/24예), 고관절 13.7% (72/526예), 척추 9.6% (14/146예), 슬관절 및 하퇴 3.5% (20/577예), 족부 및 족관절 2.5% (5/199예), 견주관절 2.4% (11/457예), 전완 및 수부 1.6% (3/189예)였다. 여성인 경우와 질환으로 수술하는 경우 입원 후 섬망이 빨리 발생하였고, 치매와 주요 우울 장애가 있는 경우 섬망 지속기간이 길게 나타났다. 결론: 외상으로 인해 수술한 경우, 두 부위 이상 수술을 받은 경우 섬망 발생 빈도가 높았고, 단일 부위에서 고관절, 척추, 슬관절 순서로 높았다. 본 연구를 통해 술 후 섬망 발생의 위험도를 예측하고 교정 가능한 인자에 대한 적극적 개입이 필요할 것으로 생각된다. Purpose: To investigate the incidence and associated factors of delirium after orthopedic surgery. Materials and Methods: A total of 2,122 cases, who were older than 20 years and underwent orthopedic surgery at a single medical center during a one year period were included. Among them, 132 patients who were diagnosed with delirium after surgery under the Diagnostic and Statistical Manual of Mental Disorders-V criteria and medicated under the consultation of a psychiatrist were included in the study The differences in the incidence of delirium and several affecting factors were analyzed. Results: The overall incidence of delirium after surgery was 6.2% (132 in 2,122 cases). The mean age of the delirium group was 77.4 years (range, 54–92 years), which was higher than that of the non-delirium group (58.1 years). The percentage of women in the delirium group was 63.6% (84 in 132 cases), which was higher than that of the women in the non-delirium group (49.0%). The incidence of delirium after surgery was 9.3% (85 in 916 cases) due to trauma and 3.9% (47 in 1206 cases) due to disease. The incidence of postoperative delirium according to the surgical region was 29.2% (7 in 24 cases) in two or more regions, 13.7% (72 in 526 cases) in the hip, and 9.6% (14 in 146 cases) in the spine, 3.5% (20 in 577 cases) in the knee-lower leg, 2.5% (5 in 199 cases) in the foot-ankle, 2.4% (11 in 457 cases) in the shoulder-elbow, and 1.6% (3 in 189 cases) in the forearm-wrist-hand. Delirium occurred more rapidly in women and surgery due to disease, and the duration of delirium was longer in patients with dementia and major depressive disorders. Conclusion: The incidence of postoperative delirium was high in cases of surgery due to trauma and in cases of surgery in two or more sites. The incidence of postoperative delirium according to a single surgical region was higher in the order of the hip, spine, and knee. Active intervention is needed regarding the correctable risk factor.
지락고장에 의해 금속제 유연전선관에 유도된 개폐서지전압의 특성
이복희(Bok-Hee Lee),신건진(Gun-Jin Shin),박희열(Hee-Yeoul Park),엄상현(Sang-Hyun Um),김유하(You-Ha Kim) 한국조명·전기설비학회 2013 조명·전기설비학회논문지 Vol.27 No.5
This paper presents the transient behavior of the switching surge voltages generated by interruption of DC ground fault currents flowing through metal flexible conduits. All fault circuits consist of line parameters such as resistance, inductance, capacitance and conductance. The use of nonmagnetic metal conduits should be taken into account in order to reduce the inductance of battery charger distribution circuits. The frequency-dependent circuit parameters of metal flexible conduits were measured. The switching surge voltages generated at the ground fault circuit consisted of steel-galvanized alloy and aluminium conduits were investigated. As a result, the impedances of metal flexible conduits are significantly increased over the range of the frequency above 10 kHz and the switching surge voltages generated along aluminium flexible conduit are lower than those along steel-galvanized alloy conduit when DC fault current is interrupted.
탄소접지극 접지임피던스의 주파수의존성과 과도응답특성의 해석
이복희(Bok-Hee Lee),이강수(Kang-Soo Lee),김유하(You-Ha Kim),엄상현(Sang-Hyun Um) 한국조명·전기설비학회 2013 조명·전기설비학회논문지 Vol.27 No.2
This paper presents transient response behavior and frequency-dependent ground impedance of a single carbon ground electrode. The ground impedance of the carbon ground electrode was measured as a function of frequency of injected currents and simulated by using the distributed parameter circuit model with due regard to the frequency-dependent soil parameters, and the transient response behavior of the carbon ground electrode against impulse currents were investigated. As a consequence, the frequency-dependent ground impedance of the carbon ground electrode showed the capacitive behavior, that is, the ground impedance decreases with increasing the frequency of injected currents and lowers at the fast front time of impulse current. It was found that the carbon ground electrode is effective in grounding system for lightning protection. The ground impedance simulated with due regard to the frequency-dependent soil parameters was in good agreement with the measured data. The adequacy of the simulation technique and the distributed parameter circuit model for the carbon ground electrode was verified. It is expected that the simulation methodology, which analyzes the frequency-dependent ground impedance of the carbon ground electrode proposed in this work, can be used in the design of a grounding system for protection against lightning.