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서철헌 崇實大學校 2000 論文集 Vol.30 No.1
In this paper, a 1*4 active phased array antenna was designed using the voltage controlled oscillators(VCO) with the varactor diode and the transmission line network with open stub. The varactor diode was connected in parallel to the FET for the wide tuning range of the VCO and the open stubs were connected at the end of the transmission line network to increase the scan range. The scan range, -20 degree to 22 degree at 2.44GHz, was controlled by the applied varactor diode voltage and the transmission line coupling network.
초고속 위성통신을 위한 IF 모듈 설계 및 제작에 관한 연구
서철헌 崇實大學校 生産技術硏究所 2001 論文集 Vol.31 No.-
As the bandwidth in increased, the difference in frequency between a DC and desired siginal is decreased. It indicates the difficult design of a band pass filter for reject to a LO leakage signal and a image signal. This thesis study the suppression of a LO leakage. The research is applied in the Ka Band satellite communication ATM module with a 155Mbps signal bandwidth. This study use a Sub Harmonic Image Rejection Mixer for a LO suppression.
서철헌 崇實大學校 生産技術硏究所 2002 論文集 Vol.32 No.-
In this paper, the design of dual mode power amplifier that operates on wireless LAN and IMT-2000 service is described. Final output is 1watt. Two different active components are used for the dual mode operation, and they are combined with the bias control circuits. By the voltage variation of the mode control voltage V_m, the conversion between two modes are achieved. When the control voltage is low, the amplifier is operated at the band of wireless LAN, oppositely, when the control voltage is high, the amplifier is operated at the band of IMT-2000. Two output ports was combined with the circuit using Photonic Band Gap pattern and bandpass filter.
Hun-Chul Seo,Chul-Hwan Kim,Sang-Bong Rhee,Jae-Chul Kim,Ok-Bae Hyun IEEE 2010 IEEE transactions on applied superconductivity Vol.20 No.4
<P>A conventional superconducting fault current limiter (SFCL) is usually only connected to a power system for fault current limitation. The study described in this paper, however, attempts to use the hybrid SFCL application to reduce the transformer inrush current. To accomplish this, this paper first suggests the concepts to expand the scope of the SFCL application in the power system. The power system operator should first determine the proper amount of current-limiting resistance (CLR) of the hybrid SFCL. Therefore, this paper suggests a decision scheme of the optimal insertion resistance in an SFCL application to reduce the transformer inrush current. This scheme and the SFCL model are implemented using the electromagnetic transient program (EMTP). We determine the optimal CLR by EMTP simulation, and this value is applied to model the SFCL by the EMTP. The simulation results show the validity and effectiveness of the suggested scheme and the ability of the SFCL to reduce the inrush current.</P>
Seo, Hun-Chul,Rhee, Sang-Bong Elsevier 2018 International journal of electrical power energy s Vol.97 No.-
<P><B>Abstract</B></P> <P>Most distribution systems are operated in an unbalanced state; hence, neutral currents can be generated by unbalanced currents in three-phase four-wire distribution systems. This paper proposes a novel adaptive reclosing scheme that uses the neutral current in a distribution system with a battery energy storage system (BESS). The BESS, which operates as an uninterruptible power supply, is connected to the load side. In the proposed scheme, there are two circuit breakers (CBs) at the source and load sides. The wavelet transform of neutral current is performed using symlets 5 mother wavelet at level 2. The summation of the absolute values of level 2 detail coefficients is calculated, and the absolute value of the differentiation of this summation is proposed as a new index for detecting fault clearance. The CB at the source side is reclosed after detecting fault clearance using ADSum. Then, the CB at the load side is reclosed after the completion of a synchronism check. To verify the proposed scheme, the BESS is modeled using the ATP-ElectroMagnetic Transients Program. In addition, various simulations are conducted according to fault types and fault clearance times. Simulation results show that successful adaptive reclosing is possible in the distribution system with the BESS.</P> <P><B>Highlights</B></P> <P> <UL> <LI> This paper proposes a novel adaptive reclosing scheme in the distribution system with BESS. </LI> <LI> A new index using wavelet transform is proposed to detect the fault clearance. </LI> <LI> The system configuration and algorithm for the proposed adaptive reclosing scheme are discussed. </LI> <LI> The proposed technique is verified by simulating the various fault clearing time and fault types. </LI> </UL> </P>
Applicability of Messenger Wire for Purpose of Lightning Protection
Hun-Chul Seo,Joon-Han,Sun-Kyu Choi,Byung-Sung Lee,Sang-Bong Rhee,Chul-Hwan Kim 대한전기학회 2016 Journal of Electrical Engineering & Technology Vol.11 No.1
The Korean distribution line currently consists of overhead ground wires (OHGW), overhead distribution lines, neutral wires (NW), and messenger wires (MW). The MW is installed under the NW. The lightning protection system in Korea is focused on OHGW and lightning arrester and the MW are not considered. Therefore, this paper proposes the applicability of MW for purpose of lightning protection. For this, we analyzed the effects of lightning overvoltage according to the existence of OHGW and MW and the grounding conditions of the MW in the Korean distribution system. The grounding conditions of the MW that we took into consideration were the common or separate grounding of the MW and NW. The analysis based on the equivalent circuit of the distribution pole at each condition was performed. The distribution lines and lightning were modeled using the Electromagnetic Transients Program (EMTP). For each of the installation conditions of the OHGW and MW, the various lightning conditions were simulated and analyzed for both direct and indirect lightning. The simulation results showed that, if the OHGW was not installed in the Korean distribution system, the lightning overvoltage could be reduced by the common grounding of the MW and NW.
New Simulation Method of Flashover Rate by Connection of EMTP and MATLAB
Seo, Hun-Chul,Han, Joon,Choi, Sun-Kyu,Lee, Byung-Sung,Kim, Chul-Hwan The Korean Institute of Electrical Engineers 2016 Journal of Electrical Engineering & Technology Vol.11 No.3
Because of the random characteristics of lightning, the Monte Carlo method is applied to estimate the flashover rate due to lightning, however, the simulations using previous methods are difficult to both beginner and expert in power corporations. Therefore, this paper proposes the new and easy method to simulate the flashover rate by connection of electromagnetic transients program (EMTP) and MATLAB. The magnitude of a lightning strike is based on a curve measured in the field, while the classification of direct and indirect lightning depends on the striking distance. In a Korean distribution system, the flashover rate induced by lightning is simulated using proposed method. Simulations of the footing resistance according to the existence of an overhead ground wire (OHGW) are performed and the simulation results are discussed. The simulation results are compared with findings obtained with the IEEE Flash 2.0 program.
Phased Array Antenna Using Active Device
Seo, Chul-Hun The Korean Institute of Electrical Engineers 2004 KIEE International Transactions on Electrophysics Vol.4C No.6
This paper presents a new active antenna consisting of a microstrip patch for the passive radiator, a mixer for frequency conversion, a voltage controlled oscillator (VCO) and a phase detector for phase control. The microwave signal frequency has been converted into intermediate frequency (IF) on the antenna elements by the mixer. The active antenna consists of two ports, the IF port has a transmitted IF signal via power combined to the baseband and the dc control port is under the control of the phase-detector. The input voltage of the VCO is controlled by the phase detector. The scan range of the array is determined by the phase detector and the VCO and is obtained between 30$^{\circ}$ and - 30$^{\circ}$