• Journal of Electrical Engineering and Technology
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• 제7권3호
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• pp.312-319
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• 2012

The life of a power transformer is dependent on the life of the cellulose paper, which influenced by the hot spot temperature. Thus, the determination of the cellulose paper's life requires identifying the hot spot temperature of the transformer. Currently, however, the power transformer uses a heat run test is used in the factory test to measure top liquid temperature rise and average winding temperature rise, which is specified in its specification. The hot spot temperature is calculated by the winding resistance detected during the heat run test. This paper measures the hot spot temperature in the single-phase, 154kV, 15/20MVA power transformer by the optical fiber sensors and compares the value with the hot spot temperature calculated by the conventional heat run test in the factory test. To measure the hot spot temperature, ten optical fiber sensors were installed on both the high and low voltage winding; and the temperature distribution during the heat run test, three thermocouples were installed. The hot spot temperature shown in the heat run test was $92.6^{\circ}C$ on the low voltage winding. However, the hot spot temperature as measured by the optical fiber sensor appeared between turn 2 and turn 3 on the upper side of the low voltage winding, recording $105.9^{\circ}C$. The hot spot temperature of the low voltage winding as measured by the optical fiber sensor was $13.3^{\circ}C$ higher than the hot spot temperature calculated by the heat run test. Therefore, the hot spot factor (H) in IEC 60076-2 appeared to be 2.0.

• 대한화학회지
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• 제8권2호
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• pp.85-87
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• 1964

Alloxan에 의한 Amino acids의 spot test에 있어서, alloxan수용액에 lactose를 가해주면, alloxan 자신의 착색을 막을 수 있다. lactose를 포함하는 alloxan수용액은 매우 안정하여서, 실온에서 수 개월 동안 두어도 착색되지 않으며, lactose의 존재로 말미암아, alloxan과 amino acids와의 색반응은 조금도 영향을 받지 않았다. 이시약에 의한 amino acids의 spot test법은 ninhydrin에 의한 spot test보다 예민하고, 또 alloxan 또는 dimethylalloxan을 발색약으로 사용하는 paper chromatography법에 비해, proline (1 ${\gamma}$), hydroxyprolin (5 ${\gamma}$)를 확인할 수 있다는 장점을 가지고 있다.

• Journal of Electrical Engineering and Technology
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• 제8권1호
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• pp.156-162
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• 2013

This paper measures the hot spot temperatures in a single-phase, 154 kV, 15/20 MVA power transformer filled with natural ester fluid using optical fiber sensors and compares them with those calculated by conventional heat run tests. A total of 14 optical fiber sensors were installed on the high-voltage and low-voltage windings to measure the hot spot temperatures. In addition, three thermocouples were installed in the transformer to measure the temperature distribution during the heat run tests. In the low-voltage winding, the hot spot temperature was $108.4^{\circ}C$, calculated by the conventional heat run test. However, the hot spot temperature measured using the optical fiber sensor was $129.4^{\circ}C$ between turns 2 and 3 on the upper side of the low-voltage winding. Therefore, the hot spot temperature of the low-voltage winding measured using the optical fiber sensor was $21.0^{\circ}C$ higher than that calculated by the conventional heat run test.

• Journal of Welding and Joining
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• 제15권4호
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• pp.143-153
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• 1997

In this study, bending test was performed on the real-scale, built-up beam test model fabricated by the $CO_2$ arc spot welding to evaluate the applicability of the welding method to the production of the stiffened plate in car-carrying ship. The built-up beam models which were fixed at both ends in longitudinal direction or simply supported to the rigid foundation, depending on the restraint condition of the corresponding car decks considered, were subjected to simulated design vehicle loads or concentrated point loads. During the test, the central deflection and the longitudinal bending stresses were measured from several points on the longitudinal flange face to predict the section properties of the built-up beams. The longitudinal bending stress on each spot weld were also measured to calculate the average horizontal shear force subjected to spot welds. Test results revealed that the shear strength of spot welds with their current weld nugget size and welding pitch was adequate enough to withstand the horizontal shear forces under the design vehicle loads. Although the built-up beam fabricated by the arc spot welding was a discontinuous beam, its mechanical behavior was well explained by the continuous beam theory using the effective breadth of plate. Based on test results, the criterion for the size of spot weld of which the average shear stress might meet the allowable stress requirement of AWS Code could be established.

• Journal of Welding and Joining
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• 제28권2호
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• pp.66-73
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• 2010

Conventional fracture test of resistance spot weld had been performed without consideration of paint baking process in automobile manufacturing line. This study was aim to investigate the effect of paint baking on fracture mode and load carrying capacity in fracture test for resistance spot welded 780TRIP steels. With paint baking cycle after resistance spot welds, peel tests and microhardness were conducted on the as-welded and baked samples. Resistance spot welds in AHSS (Advanced High Strength Steels) are prone to display partial interfacial fractures during fracture test or vehicle crash. Baking cycle increased the load-carrying capacity of the resistance spot welded samples and improved the fracture appearance from partial to full button fracture for the L-type peel tests. Specially, the differences in fracture appearance are apparent when the nugget size of spot welds is small enough to produce the partial interfacial fracture. The comparison of macrohardness and microstructure between as-welded and baked samples showed that there are no large difference in change the fracture mode. However, the results of the instrumented indentation test suggested that fusion zone and HAZ of baked sample have less tensile and yield strength and proves that the tempering effects are applied and enhanced the resistance to fracture on welds with application of baking cycle.

• Journal of Welding and Joining
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• 제20권1호
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• pp.55-61
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• 2002

The automobile is made up of about twenty thousand parts. Some parts are formed by pressing and combined by spot welding. Among them, steel palate of fuel tank is formed in the metal mold and bending parts are jointed by spot and seam welding. To find weldability conditions of spot welding, clearance between two welding steel plates was made and after spot welding, weldability is evaluated by means of tensile shear load, nugget size and shape. Specimen used in this study was a mild steel of 1.2mm thickness and electrode was Cu-Cr alloy of 6mm diameter. When spot welding started, the clearance of two steel plates was changed 0mm, 3mm and 5mm step by step. The fractured surface of specimen after this test was observed by Optical Microscope to measure microstructure and nugget shape. When clearance of two specimen was 3mm and 5mm, strength and nugget size was decreased and nugget shape was not clear.

• 약학회지
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• 제11권1_2호
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• pp.4-6
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• 1967

Cation exchange resin particles amberlite IRC-50 were used as a medium for a identific test of alkaloids with dragendorff reagent. The procedures were as follows; A few particles of amberlite IRC-50 were added to the small portion of sample solutions on a spot plate or in a test tube. After 20 minutes-an hour, a drop of dragendorff reagent were added to particles of resin that were adsorbed. When alkaloid was present, the original color of the resin particles changed instantly to red or reddish orange depending on the amount and kind of alkaloid, while in the absence of alkaloid the original color of the resin particles changed light yellow. These methods were more sensitive than the ordinary spot test or paper spot test for alkaloid. The limits of identifications of nine alkaloids were tested by these methods and compared with the paper spot test method.

• 수산경영론집
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• 제37권1호
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• pp.95-110
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• 2006

Japan's frozen shrimp future market is the only fisheries future commodity market in the world. This empirical study examines the lead and lag relationship between Japan frozen shrimp spot and future markets using the daily prices from August 1, 2002 to December 31, 2005. Frozen shrimp future contract is listed on Japan Kansai Commodities Exchange. Japan imports approximately 250,000 tons of frozen shrimp annually, of which just under 70,000 tons, nearly 30%, are black tiger shrimp. Approximately 90% of black tiger shrimp are caught in Indonesia, India, Thailand and Vietnam, and the two largest consumers of these shrimp are Japan and the U.S.A. Kansai Commodities Exchange adopts the India black tiger shrimp as standard future commodity. We use unit root test, Johansen cointegration test, Granger causality test, Vector autoregressive analysis and Impulse response analysis. However, considering the long - term relationships between the level variables of frozen shrimp spot and futures, we introduced Vector Error Correction Model. We find that the price change of frozen shrimp futures with next 1, 2, 3, 4, 5 month maturity have a strong predictive power to the change of frozen shrimp spot and the change of frozen shrimp spot also have a predictive power to the change of frozen shrimp with next 1, 2, 3 month maturity. But, the explanatory power of the frozen shrimp futures is relatively greater than that of frozen shrimp spot.

• Journal of Welding and Joining
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• 제16권2호
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• pp.84-92
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• 1998

On this study, the variations of hardness and microstructure were observed at he spot-welded part of 5182 alminum alloy sheets with thickness of 1.2 mm. The hardness of spot-welded part of aluminum alloy indicated the lowest value at nugget center. Also, the position where fatigue crack exists was investigated by surveying microstructure of the spot-welded sections. Mean load-deformation diagrams were obtained from static tensile test. Fracture was occurred completely within 5 mm after transforming elastic into plastic area. Fatigue test was stopped when the specimens of fatigue test had the final displacement of 0.2mm and measured fatigue bending angle and crack length. This study utilized them, investigated the relations between fatigue bending angle and fatigue crack length and made a estimation of the fatigue fracture life of resistance spot welded part of 5182 aluminum alloy sheet. The relative equation o fatigue crack length and fatigue failure life can be represented by {TEX}$L_{C}${/TEX}=α{TEX}$N_{f}^ {β}${/TEX}.

• 한국산학기술학회:학술대회논문집
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• 한국산학기술학회 2011년도 추계학술논문집 2부
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• pp.604-606
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• 2011

Purpose This study analyzes resistance spot weldability of DP60 steels. Methodology To compare the resistance spot weldability of DP60 steels, tensile strength test and macro-section test were conducted for the resistance spot welds. Acceptable welding conditions were determined as a function of the resistance spot welding process parameters such as electrode force, welding time, and welding current. The lower limit of the welding lobe was the minimum shear tension strength for 590MPa-grade steel while the upper limit was determined whether or not expulsion was detected. Findings Welding force is 200kgf more appropriate in terms of 300kgf the larger the width of the welding zone. Acceptable welding current condition and welding lobe were changed depending on welding force. Research limitations This study is forced on inverter DC resistance spot weldability of 590Mpa-grade steels for automotive application. Practical implications This study confirms the weldability of DP60 steel by comparing resistance spot weldability depending on welding force. Originality This study analysed resistance spot weldability depending on welding force. wedability of DP60 steel were determined by welding lobes.