• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 추계학술대회 논문집 Vol.16
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• pp.539-542
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• 2003

Recently, the polymer insulators which are being used for high voltage applications have some advantages such as light weight, small size, vandalism resistance, hydrophobicity and easy making process. During outdoor service of polymer insulators, the surface of the insulating material is frequently subjected to moisture and contamination which lead to the well known phenomenon of dry band arcing. Their tracking resistance, erosion resistance, end sealing and shed design are very important because dry band arcing causes degradation of polymer surface. The shape design of porcelain insulator is formalized but design standard for polymer insulator is no standardized up to now, much research is necessary in real condition. In this paper, the aging property of polymer insulator with shed shape(regular, alternative type) is analyzed through numerical analysis, CEA(canadian electricity association) tracking wheel test and IEC 61109 Annex C.

• Applied Science and Convergence Technology
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• 제26권4호
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• pp.66-69
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• 2017

Physically implanted surface islands of Nano Carbon Tube (NCT) and ${\alpha}-F_2O_3$ particles have been produced on Al-doped ZnO (AZO)/glass surfaces by simple and direct ND:YAG laser beam irradiation. Sheet resistance of the reconstructed surface increased by about 3.6% of over AZO. Minimal surface damage can be repaired by ND:YAG laser beam irradiation in conjunction with proper impurities. Implanted islands of NCT, which are considered to be a good conductive impurity, on AZO increased the sheet resistance by about 1.8%, while implanted islands of ${\alpha}-F_2O_3$, an insulating impurity, on AZO increased sheet resistance by about 129% compared with a laser beam treated AZO. This study provides insight regarding surface implantations of nanowires and micro-circuits, doping effects for semiconductors and optical devices, surface area and impurity effects for catalysis.

• Corrosion Science and Technology
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• 제21권6호
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• pp.487-494
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• 2022

Anodizing is a typical electrochemical surface treatment method that can improve the corrosion and insulating properties of aluminum alloys. The anodization process can obtain a dense structure. It can be used to artificially grow the thickness of an anodization film. Aluminum 3003 alloy used in this study is the most commonly used alloy for batteries due to its high strength and excellent formability as well as its weldability and corrosion resistance. Aluminum 3003 alloy was anodized at 0 ℃ with 0.3 M oxalic acid at 20 V, 40 V, or 60 V for 1 hour, 6 hours, or 12 hours. As a result of analyzing the composition of each specimen with an Energy Dispersive Spectrometer (EDS), aluminum was converted into an oxide film. The thickness of the formed anodization film increased when the applied voltage and anodization time increased. High corrosion potential values and low corrosion current density values were observed for the thickest oxide layer. The anodization film formed by anodization acted as a protective layer. The electrical resistance increased as the applied voltage and anodization time increased.

• Journal of Electrical Engineering and Technology
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• 제10권1호
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• pp.355-363
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• 2015

HVDC technology has become popular as an economic mode of bulk power transmission over very long distances. Polymeric insulators in HVDC power transmission lines are affected by surface tracking and erosion problems due to contamination deposit, which pose a greater challenge in maintaining the reliability of the HVDC system. In addition, polymeric insulators are also naturally affected by aging due to various environmental stresses, which in turn accelerates the surface tracking and erosion problems. Research works towards the improvement of tracking and erosion resistance of polymeric insulators by adding nano-sized fillers in the base material are being carried out worldwide. However, surface tracking and erosion performance of nano-filled aged polymeric insulators for HVDC applications are not well reported. Hence, in the present work, tracking and erosion resistance of the nano $Al(OH)_3$ filled silicone rubber insulation material has been evaluated under DC voltages at different filler concentrations and aged conditions, as per IEC 60587 test procedures. Leakage current and contact angle measurements were carried out to understand the surface hydrophobicity. Moving average technique was used to analyze the trend followed by leakage current. Water aged specimen shows less tracking resistance when compared with thermal aged specimen. It is observed that nano-filler concentration of 5% is even sufficient to get better tracking/erosion resistance under DC voltages.

• 한국자기학회지
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• 제11권5호
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• pp.189-195
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• 2001

ICP 마그네트론 스퍼터를 이용하여 2.5$\times$2.5 $\textrm{cm}^2$ 넓이의 열산화막이 형성된 실리콘 기판에 총 14개의 동일한 간격으로 NiFe(170 )/CoFe(48 )/Al(13 )-O/CoFe(500 )/Ta(50 ) 구조의 junction을 형성하여 자기저항비의 균일성을 알아보았다. 각 층은 ICP 마그네트론 스퍼터를 이용하여 만들고 특히 절연층은 플라즈마 산화법으로 제작하여 TMR 소자를 만들었다. 완성된 각 소자를 외부자기장을 변화시키면서 4단자 측정법으로 기준저항, 자기저항비, 자화반전자장을 측정하였다. 균일한 박막형성에 적합한 ICP스퍼터라도 같은 공정하에서 자기저항비의 표준편차가 2.72 정도의 분포가 있었으며, 위치에 따른 각 기준저항, 자기저항비, 자화반전자장의 유의차는 없었다. 또한 기준저항이 증가함에따라 자기저항비와 자화반전자장이 증가하는 경향이 있었으며, 이러한 현상은 균일하지 못한 절연막의 형성에 기인하는 것으로 판단되었다. 균일한 성막이 가능한 ICP 스퍼터로도 위치별로 절연막층 상태의 국부적 분산에 따라 표준편차가 기준저항의 경우 64.19, 자기저항비의 경우 2.72의 변화가 발생하여 실제적인 소자의 양산을 위해서는 산화막 형성공정의 개선이나 후열처리 등에 의한 균일화 공정이 필요할 것으로 생각되었다.

• Nuclear Engineering and Technology
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• 제44권5호
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• pp.523-534
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• 2012

The objective of this study was to experimentally investigate the effect of heat curing methods on the temperature history and strength development of slab concrete exposed to $-10^{\circ}C$. The goal was to determine proper heat curing methods for the protection of nuclear power plant structures against early-age frost damage under adverse (cold) conditions. Two types of methods were studied: heat insulation alone and in combination with a heating cable. For heat curing with heat insulation alone, either sawdust or a double layer bubble sheet (2-BS) was applied. For curing with a combination of heat insulation and a heating cable, an embedded heating cable was used with either a sawdust cover, a 2-BS cover, or a quadruple layer bubble sheet (4-BS) cover. Seven different slab specimens with dimensions of $1200{\times}600{\times}200$ mm and a design strength of 27 MPa were fabricated and cured at $-10^{\circ}C$ for 7 d. The application of sawdust and 2-BS allowed the concrete temperature to fall below $0^{\circ}C$ within 40 h after exposure to $-10^{\circ}C$, and then, the temperature dropped to $-10^{\circ}C$ and remained there for 7 d owing to insufficient thermal resistance. However, the combination of a heating cable plus sawdust or 2-BS maintained the concrete temperature around $5^{\circ}C$ for 7 d. Moreover, the combination of the heating cable and 4-BS maintained the concrete temperature around $10^{\circ}C$ for 7 d. This was due to the continuous heat supply from the heating cable and the prevention of heat loss by the 4-BS. For maturity development, which is an index of early-age frost damage, the application of heat insulation materials alone did not allow the concrete to meet the minimum maturity required to protect against early-age frost damage after 7 d, owing to poor thermal resistance. However, the combination of the heating cable and the heat insulating materials allowed the concrete to attain the minimum maturity level after just 3 d. In the case of strength development, the heat insulation materials alone were insufficient to achieve the minimum 7-d strength required to prevent early-age frost damage. However, the combination of a heating cable and heat insulating materials met both the minimum 7-d strength and the 28-d design strength owing to the heat supply and thermal resistance. Therefore, it is believed that by combining a heating cable and 4-BS, concrete exposed to $-10^{\circ}C$ can be effectively protected from early-age frost damage and can attain the required 28-d compressive strength.

• 전기학회논문지
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• 제57권1호
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• pp.82-87
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• 2008

It is impossible to database(DB) the patterns of power cable events and cause analysis of faulted cable because the product liability(PL) law have been enforced in Korea, since 2002. In additions, simulation and pattern of power cable events are needed for DB system under accelerated deterioration. In this paper, we tested for resistance to cracking of cable below the 22.9kV class due to thermal stresses. This method of exam is following IEC 60811-3-1(Common test methods for insulating and sheathing materials of electric cables). From the results, The 22.9kV calss A power cable was discolored on the surface and significantly reduced in the longitudinal direction. As the thermal weight properties of A power cable was definitely varied, we are able to guess the problem of manufacture. If the cable was defect by the manufacture, the victims would be able to claim for damage in the PL system.

• 한국응용과학기술학회지
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• 제30권3호
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• pp.472-479
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• 2013

The conductive polymer composites recently became increasingly to many fields of industry due to their electrical properties. To understand these properties of composites, electrical properties were measured and were studied relatively. Electrical conductivity measurements showed percolation phenomena. Percolation theories are frequently applied to describe the insulator-to-conductor transitions in composites made of a conductive filler and an insulating matrix. It has been showed both experimentally and theoretically that the percolation threshold strongly depends on the aspect ratio of filler particles. The critical concentration of percolation formed is defined as the percolation threshold. This paper was to study epoxy resin filled with copper. The experiment was made with vehicle such as epoxy resin replenished with copper powder and the study about their practical use was performed in order to apply to electric and electronic industry as well as general field. The volume specific resistance of epoxy resin composites was 3.065~13.325 in using copper powder. The weight loss of conductive composites happened from $350^{\circ}C{\sim}470^{\circ}C$.

• 한국재료학회지
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• 제21권9호
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• pp.477-481
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• 2011

Composites of insulating polyethylene and carbon black are widely used in switching elements, conductive paint, and other applications due to the large gap of resistance value. This research addresses the critical exponent of dielectric breakdown strength of polymer matrix composites (PMC) made with carbon black and polyethylene below the percolation threshold (Pt) for the first time. Here, Pt means the volume fraction of carbon black of which the resistance of the PMC is transferred from its sharp decrease to gradual decrease in accordance with the increase of carbon-black-filled content. First, the Pt is determined based on the critical exponents of resistivity and relative permittivity. Although huge cohesive bodies of carbon black are formed in case of being less than the Pt, a percolation path connecting the conducting phases is not formed. The dielectric breakdown strength (Dbs) of the PMC below Pt is measured by using an impulse voltage in the range from 10 kV to 40 kV to avoid the effect of joule heating. Although the observed Dbs data seems to be well fitted to a straight line with a slope of 0.9 on a double logarithm of (Pt-$V_{CB}$) and Dbs, the least squares method gives a slope of 0.97 for the PMC. It has been found that finite carbon-black clusters play an important role in dielectric breakdown.

• Journal of Magnetics
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• 제6권4호
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• pp.132-141
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• 2001

The switching characteristics and the magnetization-flop behavior in magnetic tunnel junctions exchange biased by synthetic antiferromagnets (SyAFs) are investigated by using a computer simulations based on a single-domain multilayer model. The bias field acting on the free layer is found to be sensitive to the thickness of neighboring layers, and the thickness dependence of the bias field is greater at smaller cell dimensions due to larger magnetostatic interactions. The resistance to magnetization flop increases with decreasing cell size due to increased shape anisotropy. When the cell dimensions are small and the synthetic antiferromagnet is weakly, or not pinned, the magnetization directions of the two layers sandwiching the insulating layer are aligned antiparallel due to a strong magnetostatic interaction, resulting in an abnormal magneto resistance (MR) change from the high-MR state to zero, irrespective of the direction of the free-layer switching. The threshold field for magnetization-flop is found to increase linearly with increasing antiferromagnetic exchange coupling in the synthetic antiferromagnet. Irrespective of the magnetic parameters and cell sizes, magnetization flop does not exist near zero applied field, indicating that magnetization flop is driven by the Zeeman energy.