• Journal of Electrical Engineering and Technology
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• 제9권1호
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• pp.280-285
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• 2014

In order to evaluate the insulation deterioration in the stator windings of five gas turbine generators(137 MVA, 13.8 kV) which has been operated for more than 13 years, diagnostic test and AC dielectric breakdown test were performed at phases A, B and C. These tests included measurements of AC current, dissipation factor, partial discharge (PD) magnitude and capacitance. ${\Delta}I$ and ${\Delta}tan{\delta}$ in all three phases (A, B and C) of No. 1 generator stator windings showed that they were in good condition but PD magnitude indicated marginally serviceable and bad level to the insulation condition. Overall analysis of the results suggested that the generator stator windings were indicated serious insulation deterioration and patterns of the PD in all three phases were analyzed to be internal, slot and spark discharges. After the diagnostic test, an AC overvoltage test was performed by gradually increasing the voltage applied to the generator stator windings until electrical insulation failure occurred, in order to determine the breakdown voltage. The breakdown voltage at phases A, B and C of No. 1 generator stator windings failed at 28.0 kV, 17.9 kV, and 21.3 kV, respectively. The breakdown voltage was lower than that expected for good-quality windings (28.6 kV) in a 13.8kV class generator. In the AC dielectric breakdown and diagnostic tests, there was a strong correlation between the breakdown voltage and the voltage at which charging current increases abruptly ($P_{i1}$, $P_{i2}$).

• Journal of the Korean Wood Science and Technology
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• 제49권3호
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• pp.234-253
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• 2021

신갈나무는 국내 전역에 두루 분포되어 있는 경제, 산업적으로 활용 가치가 큰 수종이지만, 변색, 부후 등의 열화에 의한 피해가 심각하다. 이러한 이유로 신갈나무의 부후는 목재로써의 활용에 걸림돌이 되나, 부후 요인에 대한 연구는 미비한 실정이다. 본 연구에서는 신갈나무 부후에 영향하는 요인으로 곰팡이에 주목하였으며, 신갈나무의 부후 부위로부터 곰팡이를 분리, 동정하였다. 또한, 동정 된 곰팡이가 실제로 목재 열화에 영향을 미치는지 확인하기 위해 효소 활성을 평가하고, 곰팡이를 처리한 신갈나무 목재의 질량 손실을 목재 부후 실험을 통해 측정하였다. 신갈나무에서 분리된 곰팡이 5종의 genomic DNA의 ITS region을 이용한 염기서열 분석을 통해, Mucoromycota phylum에 속하는 Mucor circinelloides, Cunninghamella elegans, 그리고 Umbelopsis isabellina 3종과 Ascomycota phylum에 속하는 Ophiostoma piceae와 Aureobasidium melanogenum 2종의 곰팡이가 동정되었다. 이러한 5종의 곰팡이는 목재의 부후와 관련된 cellulase나 laccase와 같은 효소 활성이 있으며, 실제로 신갈나무의 심재와 변재의 중량을 감소시켰다. 특히, cellulase와 laccase 활성을 모두 보유한 O. piceae와 A. melanogenum는 신갈나무의 중량을 각각 6.9%와 1.5% 감소시켰다. 이러한 결과들은 본 연구에서 동정된 5종의 곰팡이가 신갈나무의 열화에 영향한다는 것을 의미하며, 신갈나무에 대한 목재 부후균으로써의 가능성을 시사한다.

• 전기학회논문지
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• 제56권12호
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• pp.2150-2156
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• 2007

According as level of industry develops day after day, electricity load system of industry requires high level control, effectiveness and high efficiency. Among supply and control unit of suitable power supply in these load characteristic, inverter systems of constant current regulate is used widely control of lighting and electric heating system. But, problems that power factor deterioration and fast response of control, efficiency, harmonics and etc are still remain. Therefore, in this paper proposed an inverter systems with constant current regulation and power factor correction (PFC) circuit for lighting and beaconing of aerodromes. The effectiveness of the proposed system confirmed through experimental results of 10[kW] power supply system.

• 대한전기학회논문지
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• 제45권4호
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• pp.553-557
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• 1996

Heat cycle aging of insulating materials in large generator stator winding has been investigated using both on-line and off-line test methods. On this study, principally, off-line test against actual generator in service was carried out to acquire information about polarization index(PI) and dissipation factor, dissipation factor tip-up, maximum partial discharge for the purpose of remnant breakdown voltage and life assessment. It was found from the tests that both dissipation factor and maximum partial discharge decreased with the increase of operating hours and starting numbers. It was found from off-line tests that the remnant breakdown voltage had a strong relationship with both dissipation factor and maximum partial discharge the remnant breakdown voltage as a results of both operating hours and starting number and the nondestructive tests were proposed as parameters which can predict the remnant lifetime of insulating materials in large generator stator windings. (author). 8 refs., 8 figs., 2 tabs.

• Geomechanics and Engineering
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• 제37권6호
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• pp.599-614
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• 2024

To evaluate the safety status of deteriorated segments in a submarine shield tunnel during its service life, a seepage model was established based on a cross-sea shield tunnel project. This model was used to study the migration patterns of erosive ions within the shield segments. Based on these laws, the degree of deterioration of the segments was determined. Using the derived analytical solution, the internal forces within the segments were calculated. Lastly, by applying the formula for calculating safety factors, the variation trends in the safety factors of segments with different degrees of deterioration were obtained. The findings demonstrate that corrosive seawater presents the evolution characteristics of continuous seepage from the outside to the inside of the tunnel. The nearby seepage field shows locally concentrated characteristics when there is leakage at the joint, which causes the seepage field's depth and scope to significantly increase. The chlorine ion content decreases gradually with the increase of the distance from the outer surface of the tunnel. The penetration of erosion ions in the segment is facilitated by the presence of water pressure. The ion content of the entire ring segment lining structure is related in the following order: vault < haunch < springing. The difference in the segment's rate of increase in chlorine ion content decreases as service time increases. Based on the analytical solution calculation, the segment's safety factor drops more when the joint leaks than when its intact, and the change rate between the two states exhibits a general downward trend. The safety factor shows a similar change rule at different water depths and continuously decreases at the same segment position as the water depth increases. The three phases of "sudden drop-rise-stability" are represented by a "spoon-shaped" change rule on the safety factor's change curve. The issue of the poor applicability of indicators in earlier studies is resolved by the analytical solution, which only requires determining the loss degree of the segment lining's effective bearing thickness to calculate the safety factor of any cross-section of the shield tunnel. The analytical solution's computation results, however, have some safety margins and are cautious. The process of establishing the evaluation model indicates that the secondary lining made of molded concrete can also have its safety status assessed using the analytical solution. It is very important for the safe operation of the tunnel and the safety of people's property and has a wide range of applications.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2002년도 학술.기술논문발표회
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• pp.7-10
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• 2002

Concrete used up to date semipermanent architecture material but now day concrete early deterioration emboss social issue because of construction structure and environmental factor. so, many study of deterioration concrete construction improve durability used impregnation alkalization agent. In These to Study of derelop reoairmeat material in reduce carbonation. xoncrete Building use Alkalinity Recovery Agent which is Realkalinity and strength surface. Alkalinity Recovery Agent undisposed application volume and cure the concrete period. To study Alkalinity Recovery Ahent spray and cure the concrete propriery in field.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.184-187
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• 2004

There are many factors that generate the early deterioration of the concrete structure. As the one of the representative factors, we can think an invasion of the water, air and so on. The water and air invade in inside void along the capillarity and they become the cause that the durability like corrosion of layer department due to freezing and thawing, inside steel frame corrosion, and so on blacks. Therefore with covering permeability covering waterproofing material of fluid condition in outer wall, intercepting the deterioration factor due to the infiltration of water from outside and for salt damage of concrete layer department, freezing damage and neutralization, it needs to improve durability of structure. This study separately examined physical and chemical specific of quality liguid siliceous of waterproofing material. Therefore as this applys the construction site, it improves the durability of concrete structure. Further this presents the application plan from the construction market against the new material.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.782-785
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• 2004

Salt attack is one of the serious deterioration factor with respect to the durability of concrete structure. Especially, in case of exposed rebar concrete structure in marine environment, corrosion of rebar is accelerated by penetration of $Cl^-$ from exterior. Through this path, volume of corroded rebar is increased about two and half times due to increased inner pressure originated from rust. As a consequence, the overall deterioration of concrete structure, namely, cracks, reduction of adhesive strength and pop-out is followed. In this paper, the effect of structure treatment of concrete on chloride resistance has been investigated. At the same time, the relationship among several characteristics, such as resistance to chloride, water absorption coefficient and surface hardness of concrete has been investigated. It is believed that surface performance improvement by the application of penetrative hardening agent influences on positively water absorption coefficient, surface hardness of concrete and resistance to chloride ion penetration.

• 한국철도학회논문집
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• 제2권3호
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• pp.61-69
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• 1999

The durability of ballast plays an important role in track behaviour. To estimate the deterioration characteristics of ballast, several tests have been carried out by several scholars. The deterioration characteristics is very important factor in the behaviour of track and its life. In this paper, abrasion/breakage characteristics of ballast is studied to see the effect of physical ballast characteristics on ballast life. To reveal breakage characteristics of ballast, the ballast box test and the MTT field test were carried out. The breakage characteristics studied in this paper is applied to the ballast life prediction in various conditions, such as LA abrasion, annual tonnage, tamping number per year, etc

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2009년도 춘계 학술대회 제21권1호
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• pp.495-496
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• 2009

콘크리트는 항온에서보다 온도의 편차가 클수록 열화가 빠르게 진행되기 때문에 열화된 콘크리트의 물성을 복구하기 위하여 사용되는 단면복구재는 외부 온도 변화에 의한 단면복구재의 품질 변화가 적거나 단면복구재에 의해 복구된 열화 콘크리트의 안정화를 유지할 수 있는 품질을 확보해야 할 필요가 있다. 본 연구에서는 일반적인 단면복구 mortar에 단열성능을 부여하여 열화 콘크리트 보수용 재료로서의 내구성능 변화에 대해 연구하였다.