• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.441-444
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• 2000

In this paper, dielectric properties of XLPE sheets of 22kV cable with semiconducting and water were investigated. The breakdown strength of XLPE under rod/needle electrode were measured at without oil. It is found that the dielectric properties such tan$\delta$ of XLPE sheet dependence on semiconducting and water layer and are decreased much lower increase with temperature. The breakdown strength and the electrode effect are obtained as a function of thickness, and a equation for the sheet thickness dependent breakdown strength is also discussion.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2256-2261
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• 2008

The electric snow melting and deicing system by electric heating cable which is adopted in this study is a part of road facilities to keep surface temperature of the road higher than freezing point of water for melting the snow or ice accumulated on it. The electric heating cables are buried under paved road at a certain depth and a certain pitch and operated automatically and manually. Design theory, amount of heating, and installation standard vary according to economic situation, weather condition, and installation place. A main purpose of this study is figuring out the appropriate range of required heat capacity and installation depth and pitches for solving snowdrifts and freezing problems with minimum electric power consumption. This study was performed under the ambient air temperature($-2^{\circ}C$, $-5^{\circ}C$), the pitches of the electric heating cables (200 mm, 300 mm), heating value ($250\;W/m^2$, $300\;W/m^2$, $350\;W/m^2$).

• Fire Science and Engineering
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• v.16 no.1
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• pp.66-76
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• 2002

This paper includes new nozzle design, basic design factors of water mist system that minimize a thermal damage of cable causing business interruption and applying underground utility tunnel. A underground concrete structure (2.5 m(H)$\times$2.5 m(W)$\times$25 m(D)) is constructed in order to test a nozzle performance. Under the designing fire scenario, critical thermal damage of cable sheath ($400^{\circ}c$) reached within a 2 minutes with unsuppressed fire, but type 1 nozzle (SMD 470 $\mu{m}$) and type 2 nozzle (SMD 650 $\mu{m}$) control cable temperature below $400^{\circ}c$. A system performance and fundamental design factors; K factor, flow rate, spray angle, size distribution, nozzle pressure, spray density are analyzed and proposed for system optimization.

• Smart Structures and Systems
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• v.20 no.2
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• pp.231-246
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• 2017

A recent work by the authors has demonstrated the feasibility of scour evaluation for Kao-Ping-Hsi Cable-Stayed Bridge simply based on ambient vibration measurements. To further attain the goal of scour monitoring, a key challenge comes from the interference of several environmental factors that may also significantly alter the pier frequencies without the change of scour depth. Consequently, this study attempts to investigate the variation in certain modal frequencies of this bridge induced by several environmental factors. Four sets of pier vibration measurements were taken either during the season of plum rains, under regular summer days without rain, or in a period of typhoon. These signals are analyzed with the stochastic subspace identification and empirical mode decomposition techniques. The variations of the identified modal frequencies are then compared with those of the corresponding traffic load, air temperature, and water level. Comparison of the analyzed results elucidates that both the traffic load and the environmental temperature are negatively correlated with the bridge frequencies. However, the traffic load is clearly a more dominant factor to alternate the identified bridge deck frequency than the environmental temperature. The pier modes are also influenced by the passing traffic on the bridge deck, even though with a weaker correlation. In addition, the variation of air temperature follows a similar tendency as that of the passing traffic, but its effect on changing the bridge frequencies is obviously not as significant. As for the effect from the alternation of water level, it is observed that the frequency baselines of the pier modes may positively correlate with the water level during the seasons of plum rains and typhoon.

• Macromolecular Research
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• v.12 no.6
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• pp.545-552
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• 2004

The long-term stability of sulfonic acid-containing polyimides has been investigated. The hydrolytic degradation of homopolyimide and the block copolyimide comprising $27\;mol\%$ of 2,2'-bis(trifluoromethyl)benzidine and $9\;mol\%$ of m-phenylenediamine (BTFMB27mPl0[7/(3+1)]), was quantified through viscosity measurements and FT-IR spectroscopic analyses. The viscosity decrease with respect to time and the degradation rate were similar. The degrees of degradation with respect to time under ambient conditions and at elevated temperature in water were monitored by FT-IR spectroscopy. A new absorption peak was observed at $1786\;cm^{-1},$ which we corresponds to the presence of anhydride end groups formed by hydrolytic scission of the imide rings.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.9
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• pp.1192-1198
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• 2014

With an increase in the penetration of offshore wind farm, the need of an accurate economic evaluation of offshore wind farm has become crucial. This paper presents an economic evaluation method of offshore wind farm in Korea reflecting the cost of offshore wind farm infrastructure (offshore substation, submarine cable and foundation) in its cost model. Each cost of offshore substation, submarine cable, and foundation is represented as a function of installed capacity, distance to shore, and water level, respectively. We have applied the method to the case study of offshore in Jeju Island and analyzed the economics under various conditions. The results show that the distance to shore is of importance in economics of offshore wind farm.

• International journal of steel structures
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• v.18 no.4
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• pp.1252-1264
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• 2018

Long span bridges such as steel cable stayed and suspension bridges are usually more flexible than short to medium span bridges and expected to have large deformations. Deflections due to live load for long span bridges are important since it controls the overall heights of the bridge for securing the clearance under the bridge and serviceability for securing the comfort of passengers or pedestrians. In case of sea-crossing bridges, the clearance of bridges is determined considering the height of the ship master from the surface of the water, the trim of the ship, the psychological free space, the tide height, and live load deflection. In the design of bridges, live load deflection is limited to a certain value to minimize the vibrations. However, there are not much studies that consider the live load deflection and its effects for long span bridges. The purpose of this study is to investigate the suitability of live load deflection limit and its actual effects on serviceability of bridges for steel cable-stayed and suspension bridges. Analytical study is performed to calculate the natural frequencies and deflections by design live load. Results are compared with various design limits and related studies by Barker et al. (2011) and Saadeghvaziri et al. (2012). Two long span bridges are selected for the case study, Yi Sun-Sin grand bridge (suspension bridge, main span length = 1545 m) and Young-Hung grand bridge (cable stayed bridge, main span length = 240 m). Long-term measured deflection data by GNSS system are collected from Yi Sun-Sin grand bridge and compared with the theoretical values. Probability of exceedance against various deflection limits are calculated from probability distribution of 10-min maximum deflection. The results of the study on the limitation of live load deflection are expected to be useful reference for the design, the proper planning and deflection review of the long span bridges around the world.

• 한국정보통신설비학회:학술대회논문집
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• 2006.08a
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• pp.105-110
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• 2006

The most sensitive part of the installed optical cable is the optical loss variation of the splicing point according to the environmental changes. This paper presents the details of the experimental results of the external environmental changes on optical loss, such as bending, temperature variation, temperature variation after water osmosis and variation. Through the bending test of optical fiber, rapid increase of optical loss was measured within the diameter of 30mm. The result of optical loss variation within the temperature range of $-30^{\circ}C{\sim}60^{\circ}C$ is less than 0.02dB. It was confirmed that the maximum optical loss increased up to 0.2dB in case of water osmosis within the temperature range of $-40^{\circ}C{\sim}80^{\circ}C$. There is small optical loss variation of 0.01dB under the 1mm vibration test. The experimental results of this paper can be used as the reference data for the design of the optical fiber cable splicing enclosure to protect the optical loss variation due to environmental changes.

• Journal of the Korean Geotechnical Society
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• v.33 no.2
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• pp.35-47
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• 2017

Thermal behavior of soils is mainly focused on thermal conduction, and the study of natural convection is very limited. Increase of soil temperature causes natural convection due to buoyancy from density change of pore water. The limitations of the analysis using fluid dynamics for natural convection in the porous media is discussed and a new numerical analysis is presented for natural convection in porous media using THM governing equations fully coupled in the macroscopic view. Numerical experiments for thermal probe show increase in the uncertainty of thermal conductivity estimated without considering natural convection, and suggest appropriate experimental procedures to minimize errors between analytical model and numerical results. Burial of submarine power cable should not exceed the temperature changes of $2^{\circ}C$ at the depth of 0.2 m under the seabed, but numerical analysis for high permeable ground exceeds this criterion. Temperature and THM properties of the seafloor are important design factors for the burial of power cable, and in this case effects of natural convection should be considered. Especially, in the presence of heat sources in soils with high permeability, natural convection due to the variation of density of pore water should be considered as an important heat transfer mechanism.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.6
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• pp.104-108
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• 2009

The insulation aging characteristics and structural analysis test were performed to analyze the correlations among the insulation deterioration, diagnostic results and the breakdown strength for the underground power cables. From the results of the degree of crosslinking test, hot-oil test etc., it could be confirmed that there were no manufacturing defects in the power cables under test. From the results of the water tree test and chemical structural analysis, it could be confirmed that the aging status of cable under test were very poor, especially for B-Phase and the degree of aging was increased in the orders of A, C and B-phase. From the above results, it could be concluded that the insulation aging characteristic analysis results were well consistent with the diagnostic and breakdown test results, and also confirmed that the diagnostic system under consideration was successful to discriminate the bad cables which is likely to cause cable system failure.