• Proceedings of the KIEE Conference
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• 2006.07a
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• pp.99-100
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• 2006

지금까지 국내 디지털 보호계전기의 성능 검증은 동작치 특성 시험 등 정특성시험(steady-state performance) 검증 위주로 수행되어 왔으며, 신규개발 디지털 보호계전기 및 신규 도입 디지털 보호계전기에 대해서는 정특성 시험과 함께 시뮬레이터를 이용한 동특성 시험을 병행하여 왔다. 동특성 시험은 보호계전기에 내장된 계전요소들의 유기적인 성능을 검증할 수 있는 시험으로서 복수 개의 보호계전요소를 탑재하고 있는 디지털 보호계전기를 검증하기 위해서는 필수적인 성능검증 수단이다. 그러나 이러한 장점들과 편리함에도 불구하고 디지털 보호계전기의 성능검증에 사용되는 계통 모델이 실 계통을 정확하게 반영하지 못할 경우 검증 결과의 신뢰성을 보장하기가 어렵다. 본 논문에서는 154kV 송전선로 보호용 디지털 보호계전기의 성능 검증을 위한 기반 구축 과정 및 결과에 대해서 기술한다.

• Proceedings of the KIEE Conference
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• 2006.11a
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• pp.384-386
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• 2006

This paper deals with tests on the reactive power output limit and the Over-Excitation Limiter (OEL) dynamics of generation unit. The suggested reactive limit test methods can identify the allowable maximum/minimum reactive power at 100% rated MW in the steady-state operation condition. The on-line OEL limit test method can identify the time characteristics of OEL with the generation output at 50% of the rated MW. These methods are validated by applying to Yang-Yang Pumped storage units of 282 MVA.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.506-509
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• 2005

An adaptive ${\alpha}-{\beta}$ tracker is proposed for tracking maneuvering targets with a track-while-scan radar system. The tracker gain is updated on-line corresponding to the adjusted process noise variance which is obtained via time averaging of the process over a sliding window. The adjusted process noise variance is used to compute the maneuverability index for the tracker gain based on the steady-state Kalman filter equation for each epoch. It is shown via simulation that the proposed approach provides robust and accurate position estimates during the target maneuver while the performance of the conventional ${\alpha}-{\beta}$ tracker is shown much degraded.

• Proceedings of the KIEE Conference
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• 1999.07f
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• pp.2543-2545
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• 1999

This Paper Presents the identification of rotor time constant using Neural Network. The difference between the rotor time constant of a controller and the actual one causes the degradation of motor performance in indirect vector control scheme. The actual value is varied by heating of motor, so on-line tuning method is necessary. Therefore, the identification using Neural Network is used in this paper. The simulation using Matlab/Simulink shows that the proposed method suitably identifies the rotor time constant in the steady state

• Journal of The Korean Astronomical Society
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• v.49 no.1
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• pp.1-8
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• 2016

The aim of this study is to describe the physical processes taking place in the solar photosphere. Based on 3D hydrodynamic simulations including a detailed radiation transfer scheme, we investigate thermodynamic structures and radiation fields in solar surface convection. As a starting model, the initial stratification in the outer envelope calculated using the solar calibrations in the context of the standard stellar theory. When the numerical fluid becomes thermally relaxed, the thermodynamic structure of the steady-state turbulent flow was explicitly collected. Particularly, a non-grey radiative transfer incorporating the opacity distribution function was considered in our calculations. In addition, we evaluate the classical approximations that are usually adopted in the onedimensional stellar structure models. We numerically reconfirm that radiation fields are well represented by the asymptotic characteristics of the Eddington approximation (the diffusion limit and the streaming limit). However, this classical approximation underestimates radiation energy in the shallow layers near the surface, which implies that a reliable treatment of the non-grey line opacities is crucial for the accurate description of the photospheric convection phenomenon.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.4
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• pp.459-465
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• 2009

This paper considers the influence of internal heat exchangers to the efficiency of a refrigerating system. These internal heat exchangers(liquid-suction or suction-line heat exchangers) can, in some cases, yield improved system performance while in other cases they degrade system performance. A steady state mathematical model is used to analysis the performance characteristics of refrigeration system with internal heat exchanger. The influence of operating conditions, such as gas cooler pressure and evaporation temperatures, superheat in the evaporator and temperature of gas cooler outlet, to optimal dimensions of the heat exchanger is also analyzed in the paper. The main results were summarized as follows : the mass flowrate of R744, inner diameter tube and length of internal heat exchanger, and effectiveness have an effect on the cooling capacity, compressor work and RCI(Relative capacity index) of this system. With a thorough grasp of these effect, it is necessary to design the R744 compression refrigeration cycle using internal heat exchanger.

• Journal of Institute of Control, Robotics and Systems
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• v.4 no.5
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• pp.585-591
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• 1998

It is proposed a new compensation method in the rotor time constant of indirect vector controlled induction motor. The proposed scheme is an on-line method using the stator current error that is the difference between current command and estimated current calculated from terminal voltages and currents. As the current error becomes to zero, the rotor time constant in the vector controller approaches the real value. The proposed method shows good performances in the transient region as well as in the steady state region regardless of load torque variation, and it is verified by the computer simulation using SIMULINK in Matlab.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.1619-1625
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• 2007

This paper deals with the heat transfer characteristics due to a fire of train standing at under-ground station. In order to analyze the fluid characteristics at under-ground station, the governing equation was assumed to be steady-state, incompressible and turbulent fluid model. The commercial Fluent ver. 6.0 was used to solve the above numerical problem. Through the numerical analysis, fluid path-line, temperature distribution and $CO_2$ density distribution are demonstrated for three kinds of cases. As a conclusion of the study, a scenario for operation of ventilation fan in a fire is proposed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.140-143
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• 1997

The present study is concerned with the hydrostatic extrusion process of copper-clad aluminium bar to investigate the basic flow characteristics. Considering the bonding mechanism of bi-metal contact surface as cold pressure welding, the normal pressure and the contact surface expansion are selected as process parameters governing the bonding condition. The critical pressure required for the bonding at the interface is obtained by solving a "local extrusion" using a slip line meyhod. A viscoplastic finite element method is used to analyze the steady state extrusion process. The boundary profile of bi-metal rod is predicted by tracking a particle path adjacent to interface surface. The variations of contact surface area and the normal pressure along the interface profile are predicted and compared to those by experiments.

• Journal of Industrial Technology
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• v.19
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• pp.217-226
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• 1999

A single phase to three phase power converter with cost effective and simple structure is proposed. The converter consists of rectifier and inverter. The rectifier is composed of a half wave rectifier, a dc link capacitor, and a current limiting inductor, and the inverter is of only two switches with PWM control. For negative sequence operation the inverter output voltage leads the line input by $60^{\circ}$, and for positive sequence operation the inverter output voltage leads by $60^{\circ}$. We can see that positive sequence operation shows higher output voltage, slight harmonic distortion(2%), and better performances such as high efficiency and high power factor. A mathematical model for system analysis is provided, and specifications for selection and control scheme both for start-up and for steady state are analyzed. comparison and operational limits of positive and negative sequence operation are performed, and simulations and experiments are executed to verify the proposed.