• KIEE International Transactions on Power Engineering
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• v.4A no.3
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• pp.146-151
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• 2004

The most widely used primary protection for the internal fault detection of the power transformer is current ratio differential relaying (CRDR) with harmonic restraint. However, the second harmonic component could be decreased by magnetizing inrush when there have been changes to the material of the iron core or its design methodology. The higher the capacitance of the high voltage status and underground distribution, the more the differential current includes the second harmonic during the occurrence of an internal fault. Therefore, the conventional second harmonic restraint CRDR must be modified. This paper proposes a numerical algorithm for enhanced power transformer protection. This algorithm enables a clear distinction regarding internal faults as well as magnetizing inrush and steady state. It does this by analyzing the RMS fluctuation of terminal voltage, instantaneous value of the differential current, RMS changes, harmonic component analysis of differential current, and analysis of flux-differential slope characteristics. Based on the results of testing with WatATP99 simulation data, the proposed algorithm demonstrated more rapid and reliable performance.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.8
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• pp.701-709
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• 2001

In this days, heat pipe heat sink has been widely applied to power controllers for railway substations to remove heat from power semiconductors(diodes or thyristors). The heat pipe heat sink consists of a aluminum heating block for mounting the thyristor, 2~3 heat pipes and large number of aluminum fins. The present study was to get fundamental informations of the structure, design parameters and heat transfer performances of heat pipe heat sink. Series of operational test for a unit with 3 heat pipes were performed and its heat flow circuit was analysed from the experimentally obtained data on wall temperature distribution. Total resistance was ranged 0.02~$0.03^{\circ}C$/W for a power range from 40W to400W. The time to get the steady state was approximately longer than 20 minutes, and overshooting was not occurred during start up operation.

• Transactions of Materials Processing
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• v.18 no.1
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• pp.80-86
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• 2009

This paper presents the plastic inhomogeneous deformation behavior of bimetal composite rods during the axisymmetric and steady-state extrusion process through a conical die. The rigid-plastic FE model considering frictional contact problem was used to analyze the co-extrusion process with material combinations of Cu/Al. Different cases of initial geometry shape for composite material were simulated under different conditions of co-extrusion process, which includes the interference and frictional conditions. From the simulation results, the sleeve cladding rate at the core/sleeve interface was recorded as a distribution of diameter ratio and interference conditions, which will be useful for the investigations of the bonding process during co-extrusion process. In addition, the results of the co-extrusion, connected with the results of the variations of diameter rate and average contact pressure, demonstrate a good agreement and present the possibility of describing the parameters of the plastic zones in non-uniform deformation of these type of composite materials.

• Journal of Welding and Joining
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• v.15 no.5
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• pp.115-123
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• 1997

The buckling strength, fatigue strength, stress corrosion cracking are considerably effected on one of initial imperfections, the residual stresses produced by a circumferential weld between axisymmetric cylinders. Therefore, we study the residual stresses, plastic strain and temperature distribution with using thermal elasto-plastic analysis which are generated by a circumferential weld between axisymmetric cylinders. It is investigated that welding residual stresses have an effect on the strength of cylinder for inner and outer shell under external pressure.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.5
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• pp.1338-1346
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• 1994

The objective of this study is to investigate the effect of various parameters, such as temperature, mean current density and voltage on the performance of phosphoric acid fuel cell (PAFC) by numerical analysis. Two types of flow passages, which are Z-parallel type and Z-counter type, are evaluated to obtain the best current density and temperature distribution. Parametric studies and sensitivity analysis of the PAFC system's operation in single cell are accomplished. A steady state simulation of the entire system is developed using nonlinear ordinary differential equations. The finite difference method and trial and error procedures are used to obtain a solution.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2002.05a
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• pp.845-850
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• 2002

In this study we consider a flow-line CONWIP System with Compound Poisson Demands. The processing times of each workstation follow a Coxian-2 distribution. The demands that are not satisfied instantaneously are either backordered or lost according to the number of backordered demands that exist at their arrival instants. For this system we develop an approxi­mation method to obtain the performance measures such as steady state probabilities of the number of parts at each station, the average number of backordered demands and the proportion of the lost demands. Comparisons with simulation have shown that the approximate method provides fairly good results.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.5
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• pp.640-648
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• 1998

A numerical study has been conducted to investigate the effect of inflow supply air temperature and velocity on ventilation effectiveness in an underfloor air conditioning space. A low Reynolds number k-$\varepsilon$ model is implemented to calculate steady state turbulent velocity distributions. A step-down injection method is used to calculate local and room mean ages from transient concentrations based on the concept of the age of air. Results show that there is a significant effect of Archimedes number on ventilation effectiveness especially for cooling conditions. Reynolds number shows relatively minor effect on velocity distribution and ventilation effectiveness especially for isothermal and heating conditions. It can be concluded that underfloor air conditioning system provides good ventilation characteristics for cooling conditions because of temperature stratification in the space.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.10
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• pp.908-916
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• 2000

In this paper, the characteristics of moisture ventilation in the lithium ion battery manufacturing dry room are studied numerically using standard $k-\varepsilon$ turbulence model. Both the steady-state and the unsteady behaviors of moisture ventilation are analyzed by considering local and uniform moisture generation. In order to evaluate the characteristics of moisture ventilation, three scales of ventilation efficiency and characteristic ventilation time are presented from the numerical results. It was shown that moisture distribution was dependent strongly on the flow field. The characteristics of moisture ventilation were improved by 20% and 40% in terms of the 1st scale of ventilation efficiency (SVE1) and the 2nd scale of ventilation efficiency (SVE2), respectively, through the modifications of design variables such as the addition of inlets, outlets and partition. A significant improvement in the characteristic ventilation time and the moisture exhaust efficiency was also made by these modifications.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2017.05a
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• pp.660-661
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• 2017

We consider a discrete-time queue with batch geometric arrivals, geometric services, and retention of reneging customers, in which retention probability depends on the number of customers in the system. The steady state distribution of the number of customers in the system is derived.

• Structural Engineering and Mechanics
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• v.24 no.6
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• pp.699-707
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• 2006

In the paper, a direct method of solution of the Navier equation is presented. An orthotropic thick hollow cylinder under a one-dimensional steady-state temperature distribution and a uniform magnetic field with general types of thermal and mechanical boundary conditions is considered. The Navier equation in terms of displacement is derived and solved analytically by the direct method, and magnetothermoelastic responses and perturbation of the magnetic field vector in the orthotropic thick hollow cylinder is described. The present method is suitable for orthotropic thick hollow cylinders placed in an axial magnetic field with arbitrary thermal and mechanical boundary conditions. Finally, numerical examples are carried out and discussed.