• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.3
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• pp.296-304
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• 1998

A design method of an electromagnetic wave absorber with ferrite fins in the second layer, which has very wide band frequency characteristics and is used for single-polarized wave absorption such as TV wave etc, has been designed. To examine the effectiveness of the Equivalent Material Constants Method$(EMCM)^{[1]}$ which is approximate method, the effective complex permittivity calculated by the Hashin-Strikman formulas and the EMCM are compared. Since, furthermore, the reflectivities by the EMCM in space and the FDTD method in an rectangular waveguide agreed well each other, it has been confirmed that the proposed electromagnetic wave absorber has excellent absorption characteristics in the frequency range of 30 MHz to 5830 MHz. Thus, it can be concluded that the EMCM is usefull to design and analyze the electro-magnetic wave absorber proposed here.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.8
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• pp.942-949
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• 2012

In order to ensure the safety of the large-scale public facilities, the analysis of EMC(ElectroMagnetic Compatibility) of electronic systems included in the facilities is very necessary. The reason is that the system-level EMC of the facility could be not guaranteed, even if individual equipments included in the facility are satisfied with their EMC requirements. As a result, the system-level evaluation and analysis of EMC should be carried out in order to establish the reliable operations of safety and mission-critical electronic systems. This paper analyze the relevant legal systems of domestic and other countries, and furthermore case studies of system-level EMC approaches were analyzed in the specific applications of electric railways, building, automobile, petroleum refinery systems. And the introduction of related systems in Korea is proposed, and main parts and problems to be looked at each proposed measures are discussed. The results are expected to be utilized in the introduction of the system-level EMC engineering, and contributed in national security and the protection of people's life, body and their properties.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.10
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• pp.1364-1370
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• 2014

Power system fault analysis has been based on symmetrical component method, which describes power system elements by positive, negative and zero sequence impedance. Obtaining accurate line impedances as possible are very important for estimating fault current magnitude and setting distance relay accurately. Especially, accurate calculation of zero sequence impedance is important because most of transmission line faults are line-to-ground faults, not balanced three-phase fault. Since KEPCO has started measuring of transmission line impedance at 2005, it has been revealed that the measured and calculated line impedances are well agreed within reasonable accuracy. In case of underground transmission lines, however, large discrepancies in zero sequence impedance were observed occasionally. Since zero sequence impedance is an important input data for distance relay to locate faulted point correctly, it is urgently required to analyze, detect and consider countermeasures to the source of these discrepancies. In this paper, development of pre/post processor to ATP (Alternative Transient Program) version of EMTP (Electro-Magnetic Transient Program) for sequence impedance calculation was described. With the developed processor ATP-cable, effects of ground resistance and ECC (Earth Continuity Conductor) on sequence impedance were analyzed.

• Journal of Electrical Engineering and Technology
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• v.9 no.2
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• pp.452-460
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• 2014

Due to increased concerns for rising oil prices and environmental problems, various solutions have been proposed for solving energy problems through tightening environmental regulations such as those regarding $CO_2$ reduction. Among them, Electrical Vehicles (EVs) are evaluated to be the most realistic and effective approach. Accordingly, research and development on EVs and charging infrastructures are mainly proceeding in developed countries. Since EVs operate using electric energy form a battery, they must be connected to the power system to charge the battery. If many EVs are connected during a short time, power quality problems can occur such as voltage sag, voltage unbalance and harmonics which are generated from power electronics devices. Therefore, when EVs are charged, it is necessary to analyze the effect of power quality on the distribution system, because EVs will gradually replace gasoline vehicles, and the number of EVs will be increased. In this paper, a battery for EVs and a PWM converter are modeled using an ElectroMagnetic Transient Program (EMTP). The voltage sag and unbalance are evaluated when EVs are connected to the distribution system of the Korea Electric Power Corporation (KEPCO). The simulation results are compared with IEEE standards.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2006.05a
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• pp.522-525
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• 2006

Recently, mobile devices support multi-functions such as 3D game, wireless internet, moving pictures, DMB, GPS, and PMP. Bigger size of display device is indispensable to support these functions and higher speed of the interface is needed. However, conventional parallel interfaces between processor and display nodule are not competent enough for that high speed transfers. High-speed serial interface is beginning to appear as an alternative for parallel interface. The advantages of the serial interface are high bandwidth, small number of interconnections, low-power consumption, and good quality of electro-magnetic interference. In this paper, we implement serial interface and use it for a display module. LVDS is used for PHY layer and a defined packet is used for link layer. The feature of the implemented serial interface is the reduced number of interconnections with enough bandwidth.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.8
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• pp.1340-1346
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• 2016

Utilization of Distributed Generations (DGs) using Renewable Energy Sources (RESs) has been constantly increasing as they provide a lot of environmental, economic merits. In spite of these merits, some problems with respect to voltage profile, protection and its coordination system due to reverse power flow could happen. In order to analyze and solve the problems, accurate modeling of DG systems should be preceded as a fundamental research task. In this paper, we present a PhotoVoltaic (PV) generation system which consists of practical PV cells with series and parallel resistor and an inverter for interconnection with a main distribution system. The inverter is based on controllable current source which is capable of controlling power factors, active and reactive powers within a certain limit related to amount of PV generation. To verify performance of the model, a distribution system based on actual data is modeled by using ElectroMagnetic Transient Program (EMTP) software. Computer simulations according to various conditions are also performed and it is shown from simulation results that the model presented is very effective to study DG-related researches.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.8
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• pp.1326-1333
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• 2016

It is important to clear the fault and prevent resulting in damage to power system. Although the frequency of generator internal fault is relatively low, it can lead to incalculable damage to power system as well as generator. Especially, loss of field on generator can cause the generator to lose synchronism for a short time if it is not removed promptly. Therefore, it is needed to conduct research on loss of field relay for detecting or clearing the loss of field. However, the setting of the relay may vary in generator operator or engineer, and the relay is not coordinated well with other elements associated with loss of field. In this paper, we address specifically the coordination of positive offset mho loss of field relay which is one of the protection schemes for loss of field. Computer simulations are performed by using ElectroMagnetic Transients Program-Restructured Version (EMTP-RV) based on actual data.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.8
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• pp.1465-1471
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• 2007

The electro-magnetic wave propagates through the air in the terrestrial communications, but the acoustic wave propagates through the seawater in the underwater acoustic communication(UAC). It makes the differences between the UAC link and the well hon air communication links. In this paper, we have studied path loss, absorption and ambient noise of the ocean as a medium for UAC. We have analyzed the absorption coefficient and ambient noise level of the coastal area of South Korea and suggested a strategy for the selection of the frequency band by considering the absorption coefficient and ambient noise level. Also, we present an illustrative example of a link budget for the QPSK UAC system which has carrier frequency 25kHz, bit rate 10kbps, range 1km and BER $10^{-3}$ in the shallow water environment with an ideal AWGN assumption.

• KEPCO Journal on Electric Power and Energy
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• v.6 no.4
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• pp.393-397
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• 2020

Shunt reactor, a facility for reactive power compensation, is switched several times a day depending on the load pattern. When the circuitbreaker opens the shunt reactor over-voltage is generated by several factors which degrade the insulating performance of internal parts of the circuit-breaker and cause severe voltage stress on the equipment in the power system. Transient phenomenon occurring during the switching of shunt reactor are available in laboratories that verify the performance of the circuit-breaker by simulating the power system. However, it is difficult to measure the transient phenomenon that occurs during actual operation in actual power system due to many limitations. Therefore, this paper deals with the modeling using EMTP to analyze the reignition and current chopping which causes more severe transient recovery voltage in the small inductive current breaking in actual power systems. In addition, this paper analyzes the main phenomenon that cause circuit-breaker failure in opening shunt reactor using EMTP model.

• Journal of IKEEE
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• v.22 no.4
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• pp.1068-1072
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• 2018

In underwater communications, there are many challenges due to energy limitations, long propagation delay, low data rate, and high power loss, unlike terrestrial RF communications. Especially, the propagation delay of underwater acoustic channel is five orders of magnitude higher than in electro-magnetic terrestrial channels due to the low speed of sound(1,500m/s). Thus, the MAC protocols for terrestrial communications are not suitable for underwater network. In this paper, we studied the considerations for MAC protocol in underwater acoustic channel. Here, we concentrated on CSMA based MAC protocols. From the results, we confirmed that the number of control packets has an important effect on the performance in underwater environment. These results would be useful in designing MAC protocols for underwater acoustic communications.