• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.12
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• pp.1079-1084
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• 2002

Because complex insulation method is used in EHV(extra high voltage) insulation systems, macro Interfaces between two different bulk materials which affect the stability of insulation system exist inevitably. Interface between toughened epoxy and silicone rubber was selected as a interface in EHV insulation systems and tested AC interfacial breakdown properties with variation of many conditions to influence on electrical Properties, such as interfacial pressure, roughness and oil. Specimen was designed to reduce the effect of charge transport from electrode in the process of breakdown and to have the tangential electrical potential with the direction of the interface between epoxy and silicone rubber by using FEM(finite elements method). It could control the interfacial pressure, roughness and viscosity of oil. From the result of this study, it was shown that the interfacial breakdown voltage is improved by increasing interfacial Pressure and oil. In particular, the dielectric strength saturates at certain interracial Pressure level. The decreasing ratio of the interfacial breakdown voltage in non-oiled specimen was increased by the temperature rising, while oiled specimen was not affected by temperature.

• Proceedings of the KIEE Conference
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• 2000.11c
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• pp.488-490
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• 2000

폴리에틸렌은 우수한 특성으로 절연재료분야에 광범위하게 사용되지만, 공간전하축적과 트리진전의 단점을 가지고 있으므로 이를 개선하기 위해 첨가제, 촉매법, 혼합법 등 다양한 방법들이 시도되어왔다. 메탈로센과 같은 촉매법과 첨가제법 등은 고분자의 전기적 특성은 개선되지만 가공성이 어려워지는 둥의 개선점들이 많이 존재한다. 하지만, 혼합법은 고분자 종류의 다양성과 시료 제작의 용이성으로 인하여 성질 개선법으로 자주 연구되고 있다. 혼합으로 인하여 재료의 특성에 따라 원 고분자의 고차구조가 변화되며 이는 원시료의 절연성능에 큰 영향을 미친다. 본 연구실에서는 선형저밀도 폴리에틸렌과 에틸렌비닐아세테이트를 중량비에 따라 혼합한 필름의 전기적 특성 고찰을 위하여 이미 전기 전도 특성과 유전특성에 대해 연구하여 혼합비 70 : 30인 시료와 혼합비 50 : 50인 시료의 전기적 특성이 우수함을 확인한 바가 있다. 따라서, 본 논문에서는 절연재료의 수명을 결정짓는 전원인가법에 따른 절연파괴 특성에 대해 물성분석을 통한 고차구조의 변화와의 상관성을 조사하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.11a
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• pp.530-533
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• 2002

Blending effects for generating a pretilt angle in nematic liquid crystal (NLC) with negative dielectric anisotropy on the blended polyimide (PI) of homeotropic and homogeneous alignment surface were studied. Also, we investigated the EO performances for the advanced VA-$\pi$ cell using this homeotropic blended PI surface. A many decrease of tilt angle on the polymer surface to blend homeotropic PI and homogeneous PI with side chain type was measured, and the tilt angle decreased as blended ratio and rubbing strength increase. The blended effects for generating a pretilt angle were clearly observed, and the many decrease of tilt angle can be achieved by using the blended PI surface. The electro-optical (EO) characteristics using the advanced VA-$\pi$ cell using the homeotropic blended PI surface than that of conventional VA cell can be improved. We suggest that the developed advanced VA-$\pi$ cell on a homeotropic blended PI surface is a promising technique for the achievement of a fast response time, and a high contrast ratio.

• Journal of Magnetics
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• v.19 no.2
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• pp.155-160
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• 2014

The heating produced by the absorption of radiofrequency (RF) has been considered a secondary undesirable effect during MRI procedures. In this work, we have measured the power absorbed by distilled water, glycerol and egg-albumin during NMR and non-NMR experiments. The samples are dielectric and examples of different biological materials. The samples were irradiated using the same RF pulse sequence, whilst the magnetic field strength was the variable to be changed in the experiments. The measurements show a smooth increase of the thermal power as the magnetic field grows due to the magnetoresistive effect in the copper antenna, a coil around the probe, which is directly heating the sample. However, in the cases when the magnetic field was the adequate for the NMR to take place, some anomalies in the expected thermal powers were observed: the thermal power was higher in the cases of water and glycerol, and lower in the case of albumin. An ANOVA test demonstrated that the observed differences between the measured power and the expected power are significant.

• Journal of Magnetics
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• v.4 no.2
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• pp.52-54
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• 1999

Injection molding is one of the methods to prepare dielectromagnets-permanent magnets made from hard magnetic powder (or from mixture of powders) bonded by dielectric materials. Magnetic properties of dielectromagnets are worse than those of sintered magnets made from the same hard magnetic powders, but this type of the permanent magnet has many advantages. One of them is simpler technology-easier in comparison to the technology of sintered magnets. The injection molded dielectromagnets do not need any final treatment. This technology permits to control magnetic, thermal and mechanical properties of dielectromagnets. The main chracteristics of dielectormagnets are magnetic properties, however mechanical properties have serious influence onto a range of their applications. The main factors shaping mechanical properties have serious influence onto a range of their applications. The main factors shaping mechanical properties of dielectromagnets are the kind and quantity of resin and the technology. The purpose of this investigateion was to find the correlation between infection conditions and the mechanical properties of dielectromagnets. Influence of two parameters of injection, temperature and pressure on mechanical and magnetic properties of dielectromagnets were not significantly changed. Increasing of pressure of injection also does not influence on mechanical properties of analysed samples, however increasing of temperature of injection significantly improved both compression and bending strength.

• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1463-1465
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• 1994

The electrical characteristics of $Al/Ta_2O_5/Si$ metal-oxide-semiconductor (MOS) capacitors were studied. $Ta_2O_5$ films on p-type silicon had been prepared by ionized cluster beam epitaxy technique (ICBE). This $Ta_2O_5$ films have low leakage current, high breakdown strength and low flat band shift. In this research, a single crystalline cpitaxial film of $Ta_2O_5$ has been grown on p-Si wafer using an ICBE technique. The native oxide layer ($SiO_2$) on the silicon substrate was removed below $500^{\circ}C$ by use of an accelerated arsenic ion beam, instead of a high temperature deposition. $Ta_2O_5$ films formed by ICBE technique can be received considerable attention for applications to coupling capacitors, gate dielectrics in MOS devices, and memory storage capacitor insulator because of their high dielectric constants above 20 and low temperature process.

• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1574-1576
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• 1994

$SF_6$ gas has become an important insulation medium in modern electric power apparatus, because of its high insulation withstand levels and good arc quenching capability. For the application of $SF_6$ gas in GIS the estimation of insulation properties is a fundamental point. Moreover the reduction of withstand levels in case of inhomogeneous fields caused by particles or fixed protrusions is of special interest. It is known that the presence of free conducting particles in GIS can significantly lower the insulating level of $SF_6$ gas at elevated pressure and also it has been recently shown that dielectric strength is greatly reduced by fast transients such as disconnector surges where metallic particles are involved. In this paper, we have disigned the particle test chamber rated 362kV for the purpose of investigating the discharge characteristics in SF6 gas where inhomogenius fields are caused by metallic particles.

• Bulletin of the Korean Chemical Society
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• v.33 no.11
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• pp.3539-3543
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• 2012

Butacaine sulfate is an ester of p-aminobenzoic acid which has been widely used as a local anaesthetic and it is a long standing agent particularly for spinal anaesthesia. For this reason, a kinetic study of oxidation of butacaine sulfate by sodium N-chlorobenzenesulfonamide (chloramine-B or CAB) has been carried out in $HClO_4$ medium at 303 K in order to explore this redox system mechanistic chemistry. The rate shows a first-order dependence on both $[CAB]_o$, and $[substrate]_o$, and a fractional-order dependence on acid concentration. Decrease of dielectric constant of the medium, by adding methanol, increases the rate of the reaction. Variation of ionic strength and addition of benzenesulfonamide or NaCl have no significant effect on the rate. The reaction was studied at different temperatures and the activation parameters have been evaluated. The stoichiometry of the reaction has been found to be 1:2 and the oxidation products have been identified by spectral analysis. The observed results have been explained by plausible mechanism and the related rate law has been deduced.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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• pp.196-201
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• 2001

Electro-Rheological(ER) fluids change their apparent viscosity according to the electric field strength. Therefore, there are many practical applications using the ER fluids. ER effect on the dispersive system of polarizable fine powder/dielectric oil has been investigated. The electrical and rheological properties of starch based ER fluid were reported. Yield stress of the fluids were measured on the couette cell type rheometer as a function of electric fields, particle concetrations, and temperatures. The electric field is applied by high voltage DC power supply, The outer cup is connected to positive electrode(+) and the bob becomes ground(-). And the temperatures the viscosity(or shear stress) versus shear rates were measured. In this experiment shear rates were increased from 0 to 200s$^{-1}$ in 2 minutes. This thesis presents Bingham properties of ER fluids subjected to temperature variations. The temperature dependence of the viscosity was determined for ER fluids consisting of 35 weight % starch particles in automatic transmission oil.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.9
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• pp.783-789
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• 2003

The winding problems of traction motor are the major determinant of motor's life. The root cause of winding failure is gradual deterioration of the insulation due to thermal, electrical, mechanical and environmental stresses. The aging of the insulation reduces the electrical and mechanical strength of the insulation. At same point, a voltage surge or mechanical shock from a traction motor start will fracture or break down the insulation. To achieve the expected life usually requires extensive laboratory evaluation of the insulation systems and the use of accelerated aging tests. There are several nondestructive test available for checking, the condition of motor insulation, the probable extent of aging, and the rate of which aging is taking place. So the insulation characteristics of stator coil were each analyzed by measurement of dielectric loss(tan$\sigma$), capacitance and partial discharge. The method of diagnosis is able to analyze the insulation condition and evaluate the life of the traction motor.