• Journal of IKEEE
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• v.22 no.4
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• pp.1050-1055
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• 2018

In this paper, we analyzed the sensitivity of matching elements for the dual-band operation of a power amplifier with composite right/left-handed (CRLH) transmission lines. Metamaterial theory enables CRLH transmission to support arbitrary impedance matching at dual frequencies. In general, at sub-GHz range, the CRLH matching networks are commonly implemented with lumped elements, which are prone to manufacturing distribution. In order to reduce the effect from the distribution of element values in design, we suggest a method to analyze the sensitivity of matching elements from the performance aspect of power amplifiers. Based on the analysis, a 40dBm dual-band power amplifier operating at 0.7GHz and 1.5GHz is designed.

• KEPCO Journal on Electric Power and Energy
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• v.7 no.1
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• pp.73-77
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• 2021

As the big data analysis technologies has been developed worldwide, the importance of asset management for electric power facilities based data analysis is increasing. It is essential to secure quality of data that will determine the performance of the RISK evaluation algorithm for asset management. To improve reliability of asset management, asset data must be preprocessed. In particular, the process of cleaning dirty data is required, and it is also urgent to develop an algorithm to reduce time and improve accuracy for data treatment. In this paper, the result of the development of an automatic cleaning algorithm specialized in overhead transmission asset data is presented. A data cleaning algorithm was developed to enable data clean by analyzing quality and overall pattern of raw data.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1354-1359
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• 2007

This paper discusses the acoustic performance of simple expansion chamber using computational fluid dynamics(CFD). The CFD model consists of an axisymmetric grid with a single period sinusoid of acceptable amplitude and duration imposed at the inlet boundary condition. The time history of the static pressure is recorded at two points, one in the inlet pipe and one point in outlet pipe. The time history of the static pressure is converted to the frequency domain using Fourier Transform and the transmission loss (TL) of the muffler is obtained from the ratio of the static pressure at the inlet and outlet pipe. The transmission loss of CFD result is compared with that of the computational acoustic analysis using the boundary element method (BEM). There are some differences in two results due to the pressure drop according to the inlet and outlet pipe length. Therefore, the effects of the pressure drop to the transmission loss have to be considered.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.05a
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• pp.218-221
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• 2003

In this report, we test the features that the outside environment of subscriber lines have an effects on ADSL's electrical transmission performance with a suspected cases of line. I observed an influence of AM broadcasting jamming, and also analysis of an incoming lines of various kinds, a line distance, a connection way, Bridge Tap influencing ADSL's electrical transmis-sion performance. To have a maximum effect of Adsl electrical transmission, I came to a conclusion that we have to make use of the older copper wire cable line to fit the situation at the present and we must change it into the excellent optical fiber cable one by one.

• Journal of Electrical Engineering and Technology
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• v.11 no.2
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• pp.436-444
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• 2016

Oil-paper insulation of valve-side windings in converter transformers withstand electrical stresses combining with AC, DC and strong harmonic components. This paper presents the physical mechanisms and experimental researches on partial discharge (PD) of oil-paper insulation at pulsating DC voltage. Theoretical analysis showed that the phase-resolved distributions of PDs generated from different insulated models varied as the increase of the applied voltages following a certain rule. Four artificial insulation defect models were designed to generate PD signals at pulsating DC voltages. Theoretical statements and experimental results show that the PD pulses first appear at the maximum value of the applied pulsating DC voltage, and the resolved PD phase distribution became wider as the applied voltage increased. The PD phase-resolved distributions generated from the different discharge models are also different in the phase-resolved distributions and development progress. It implies that the theoretical analysis is suitable for interpretation of PD at pulsating DC voltage.

• Journal of Electrical Engineering and Technology
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• v.9 no.6
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• pp.2049-2057
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• 2014

In this paper, a numerical method for analyzing coupling between high-altitude electromagnetic pulse (HEMP) as external field and a shielded twisted pair (STP) cable is proposed, which is based on an expanded chain matrix. Load responses of electromagnetic (EM) field excitation in uniform transmission line (TL) are solved by Baum-Liu-Tesche (BLT) equations in frequency domain, however, it is difficult to apply BLT equations to solve load responses of STP cable because the iteratively changing configuration of each twisted pairs are involved in cable. To avoid this problem and decrease memory and CPU time, we proposed the expanded chain matrix modeling method that is calculated using ABCD parameters, and applied multi-conductor transmission line (MTL) theory to consider the EMP coupling effectiveness of each twisted pairs. The results implemented by the proposed method are presented and compared with those obtained by the finite-difference time domain (FDTD) method as a kind of 3D full wave analysis.

• Journal of Power Electronics
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• v.15 no.6
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• pp.1480-1488
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• 2015

In this paper, a revolutionary buck converter is proposed with soft-switching technology, which is realized by a coupled inductor. Both zero-voltage switching (ZVS) of main switch and zero-current switching (ZCS) of freewheeling diode are achieved at turn on and turn off without using any auxiliary circuits by the resonance between the parasitic capacitor and the coupled inductor. Furthermore, the peak voltages of the main switch and the peak current of the freewheeling diode are significantly reduced by the coupled inductor. As a result, the proposed converter has the advantages of simple circuit, convenient control, low consumption and so on. The detailed operation principles and steady-state analysis of the proposed ZVS-ZCS buck converter are presented, and detailed power loss analysis and some simulation results are also included. Finally, experimental results based on a 200-W prototype are provided to verify the theory and design of the proposed converter.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.5A
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• pp.316-322
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• 2003

We theoretically analyze the properties of nonlinear distortion due to modulation instability (MI), which is a major factor of performance degradation in optical amplified transmission systems, and propose an optical link structure to compensate MI based on the analysis. The proposed MI compensating link structure is composed of optical phase conjugators (OPCs) and dispersion compensating fibers (DCFs) in order to suppress nonlinear effects in optical transmission links. It has been confirmed through computer simulations that the performance of the proposed compensation scheme is superior to that of conventional compensation schemes for 500 km transmission.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.1
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• pp.5-14
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• 2002

In this paper, we analyze inductive interference in conductive material around 345 kV power transmission line, and evaluate the effects of mitigation wires. Finite element method (FEM) is used to numerically compute induced eddy currents as well as magnetic fields around powder transmission lines. In the analysis model, geometries and electrical properties of various elements such as power transmission line, buried pipe lines, overhead ground wire, and conducting earth are taken into accounts. The calculation shows that mitigation wire reduces fairly good amount of eddy currents in buried pipe line. To find the optimum magnetic field shielding location of mitigation wire, we applied evolution strategy algorithm, a kind of stochastic approach, to the analysis model. Finally, it was shown that we can find more effective shielding effects with optimum location of one mitigation wire than with arbitrary location of multi-mitigation wires around the buried pipe lines.

• Transactions on Electrical and Electronic Materials
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• v.4 no.3
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• pp.19-24
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• 2003

The experimental and simulation study of insulator failure by cement growth on suspended insulators (16,500kgf) for transmission line was discussed. To get more practical and analytic calculation results, the advanced program was used. This analysis tool was possible to calculate stress behaviors with mechanical loading when cement displacement happened. From simulation results, the. cement displacement changed with linear according to temperature. The shear stress was about $7 kgf/mm^2$ at $0.07\%$ displacement provided from $200^{\circ}C$, then it could be seen that the cement would be fractured even if $0.07\%$ displacement acted, because the cement had about $7-9 kgf/mm^2$ flexure strength. The curve patterns of shear stress with the increase of mechanical loading were changed at $0.02\%$ as a turning point, when the cement displacement was over $0.02\%$ the shear stresses decreased reversely with the increase of mechanical loading. From analysis on porcelain body it was known that there were enough margin to protect the fracture of porcelain body before the cement