• Proceedings of the Membrane Society of Korea Conference
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• 2002.05a
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• pp.35-41
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• 2002

Dense oxygen ionic conducting materials can be used for oxygen separation membranes at high temperatures. However, they show relatively low permeation flux because of their large resistances. To reduce resistances and improve the oxygen permeation flux, thin dense yttria-stabilized-zirconia (YSZ)/Pd composite dual-phase membranes were fabricated by a new approach that combines the reservoir method and chemical vapor deposition (CVD). A thin porous YSZ layer was coated on a porous alumina support by dip-coating the YSZ suspension. A continuous Pd phase was formed inside pores of the YSZ layer by the reservoir method. The residual pores of the YSZ/Pd layer were plugged with yttria/zirconia by CVD to ensure the gas tightness of the membranes. The oxygen permeation fluxes through these composite membrane were 2.0$\times$10$^{-8}$ mol/cm$^2$.s and 4.8$\times$10$^{-8}$ mol/cm$^2$.s at 105$0^{\circ}C$ when air and oxygen were used as the permeate gases, respectively. These oxygen permeation values are about 1 order of magnitude higher than those of pure YSZ membranes prepared under similar conditions.

• Journal of Electrical Engineering and Technology
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• v.1 no.1
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• pp.16-22
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• 2006

Selective ground relays (SGRs) are useful fur distinguishing a faulted feeder from the sound feeders in ungrounded systems. However, they sometimes mis-operate due to human or device errors. Particularly, the reversed polarity of zero-sequence current transducers (ZCTs) is the most frequent cause of mis-operation. This paper presents a modified SGR for reducing the probability of mis-operations caused by the reversed polarity of ZCTs. The modification is achieved by introducing an adaptive time delay, which depends on the magnitude of the zero-sequence current and the phase angle deviation from the reference. The modified SGR was successfully demonstrated on a sample ungrounded system without mis-operation.

• Journal of Power System Engineering
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• v.5 no.4
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• pp.61-66
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• 2001

Electro-Rheological(ER) fluids undergo a phase-change when subjected to an external electric field, and this phase-change typically manifests itself as a many-order-of magnitude change in the rheological behavior. This paper presents experimental results on material properties for an ER fluids of arabic gum components subjected to electrical fatigues. As a first step, ER fluids are made of arabic gum 25% of particle weight-concentration. Following the construction of test mechanism for estimated durability of ER fluid, the dynamic yield stress, shear stress and current density of the ER fluids are experimentally distilled as a function of DC electric field. The durability estimation of operated ER fluids are distilled and compared with those of unused ER fluids. In addition, the surface roughness of the employed electrode for copper and aluminum are evaluated as a function of the number of the electric-field cycles.

• Journal of Magnetics
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• v.16 no.4
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• pp.403-407
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• 2011

Metal-insulator type, nano-granular soft magnetic films have been reviewed from the viewpoint of high frequency magnetic materials. The formation of nano-granular structure is related to the magnitude of heat of formation of intergranule materials. Variation of the ratio of granule phase to intergranule phase in the film is found to produce various characteristics in the magnetic properties of the film. The HRTEM observation reveals that neighboring granules in the film with above 60 at.% Co, contact at considerable points and the films show soft magnetic properties which are explainable in terms of the random anisotropy model for nano-crystalline materials. Addition of Ni group elements in Co-O based films enhances their anisotropy field up to 400 Oe and they exhibit excellent frequency response of permeability. Also, large electromagnetic noise suppression effect is demonstrated as one of their potential applications.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.25 no.11
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• pp.50-57
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• 2011

This paper proposes a boost type single-phase inverter system to compensate the voltage sag appeared on source side. The proposed system is composed of a boost converter, a PWM inverter, and a bypass diode. If the voltage sag has appeared in input voltage, the boost converter would be operated to compensate it in the proposed system. The boost converter would not be operated when the magnitude of input voltage is more than 0.9 pu. The output voltage is kept constant by a direct-quadrature frame controller in the inverter. A 300 W class boost type inverter system was simulated, and the validity of the proposed system was verified by carrying out experiments.

• Bulletin of the Society of Naval Architects of Korea
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• v.17 no.1
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• pp.31-37
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• 1980

Herein the flow past a submerged circular cylinder with a free surface is mapped onto a reference plane, in which the free surface is transformed to a straight line and the cylinder to a certain shape. A global mapping function between two planes is sought in a manner that linear free-surface elevation is generated in the physical plane. Hereby the Froude mumber $F_h$, based on the submergence depth h', is assumed to be of order 0(1) and the ratio a'/h'(a'=cylinder radius) of order o(1). Wave thus obtained are slightly different in magnitude and phase from usual linear solution. The resulting free wave starts advanced ahead compared to the classical result and its amount depends on Froude number. Based on the present concept wave forces are calculated. In this type of approach the body boundary condition gives more influence on wave resistance than that by the free surface in the speed range $F_h>1$.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.55 no.11
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• pp.447-452
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• 2006

This paper presents a scheme to solve the congestion problem with phase-shifting transformer(PST) controls and power generation controls using linear programming method. A good design of PST and power generation control can improve total transfer capability(TTC) in interconnected systems. This paper deals with an application of optimization technique for TTC calculation. Linear programming method is used to maximize power flow of tie line subject to security constraints such as voltage magnitude and real power flow in interconnected systems. The results are compared with that of repeat power flow(RPF) and sequential quadratic programming(SQP). The proposed method is applied to 10 machines 39 buses model systems to show its effectiveness.

• Journal of KSNVE
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• v.9 no.2
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• pp.409-417
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• 1999

A new method is proposed for the isolation of resonances from scattered waves for the isolaton of resonances from scattered waves for acoustic wave resonance scattering problems. The resonance scattering function consisting purely of resonance information is defined. Acoustic wave scattering from a variety of submerged bodies is numerically analyzed. The classical resonance scattering theory (RST) and the new method compute identical magnitudes of the resonances from each partial wave, however, the phases are significantly different. The exact $\pi$-radians phase shifts through the resonance and anti-resonance frequencies show that the proposed method properly extracts the vibrational resonance information of the scatterer. Due to the differences in phases of the resonances from each partial wave, the new method and RST generate different total resonance spectra.

• The Journal of the Acoustical Society of Korea
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• v.17 no.2E
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• pp.10-15
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• 1998

Application of the Filtered-X LMS adaptive filter to active noise cancellation requires to estimate the transfer characteristics between the output and the error signal of the adaptive canceler. In this paper, we derive an adaptive cancellation algorithm and analyze is convergence behavior when the acoustic noise is assumed to consist of multiple sinusoids. The results of the convergence analysis of the Filtered-X LMS algorithm indicate that the effects of parameter estimation inaccuracy on the convergence behavior of the algorithm are characterize by two distinct components : Phase estimation error and estimated magnitude. In particular, the convergence of the Filtered-X LMS algorithm is show to be strongly affected by the accuracy of the phase response estimate. Simulation results of the algorithm are presented which support the theoretical convergence analysis.

• Proceedings of the KIEE Conference
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• 1994.07a
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• pp.392-396
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• 1994

A method which improves the efficiency of induction motor by controlling the input voltage by the three phase AC voltage controller is studied at the sides of theory and practice. At first, the principle of decreasing the input power and improving the efficiency by adjusting the amplitude of the input voltage according to the load rate is shown. Secondarily, the mathematical model of the three phase AC voltage controller-induction motor system is drived to translate the dynamic characteristics. The validity of the dynamic model is verified by simulation. The new driving method is also proposed, which regulates the rated speed's driving by the speed estimation from the firing angle and the magnitude reverse induced-voltage information. As a result, the digital control system is constructed. Expermintal results show desirable characteristics of proposed system.