• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• 제35권6호
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• pp.594-602
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• 2022

Cast-resin transformers are widely installed in various electrical power systems because of their low operating cost and low influence on external environmental factors. However, when they have an internal defect during the manufacturing process or operation, a partial discharge (PD) occurs, and eventually destroys the insulation. In this paper, a Rogowski-type PD sensor was studied to replace commercial PD sensors used for the insulation diagnosis of power apparatus. The proposed PD sensor was manufactured with four different types of PCB-based winding structures, and it was analyzed in terms of the detection characteristics for standard calibration pulses and the changes of the output voltage according to the distance. The output increased linearly in accordance with the applied discharge amount. It was confirmed that the hexagon structure sensor had the highest sensitivity, because the winding cross-sectional area of the sensor was larger than others. In addition, as the distance from the defect increased, the output voltage of the sensors decreased by 7.32% on average. It was also confirmed that the attenuation rate according to the distance decreased as the input discharge amount increased. For the application of this new type sensor, PD electrode system was designed to simulate the void defect. Waveforms and PRPD patterns measured by the proposed PD sensors at DIV and 120% of DIV were the same as the results measured by MPD 600 based on IEC 60270. The proposed PD sensors can be installed on the inner wall of the transformer tank by coating its surfaces with a non-conductive material; therefore, it is possible to detect internal defects more effectively at a closer distance from the defect than the conventional sensors.

• Transactions of the Korean hydrogen and new energy society
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• 제34권3호
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• pp.274-282
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• 2023

This study conducted direct numerical simulations of the natural convection phenomena of gaseous hydrogen in a physical storage container containing four circular cylinders. Rayleigh numbers (Ra) in the range of 10⁴≤Ra≤10⁶ and a Prandtl number (Pr)=0.69 (gaseous hydrogen) were considered. The main parameter is a horizontal distance of four circular cylinders and the values of ε_h=0.1, 0.2, 0.3, 0.4, and 0.5 are considered. The flow and thermal structures and corresponding heat transfer characteristics are investigated with respect to the transition of the flow regime. The time- and surface-averaged Nusselt number on the cylinder surface and the wall of physical storage container increased by about 57% and 69% according to the Ra and ε_h, respectively. Thus, the horizontal distance has an influence on the heat transfer characteristics on natural convection of gaseous hydrogen.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• 제9권1호
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• pp.37-46
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• 1995

Along with the recent trend of complexity and long distance transmission in power system, dynamic analysis of stability considering the load characteristics is an important subject. In this paper, the influence of the induction motor loads on the power system voltage is investigated. The influence of the inductive load ratio and the inertia of induction motor on the voltage response of the power system are examined, and in the case of the high percentage of the induction motor load, induction motors in the power system can lead to transient voltage instability even under the system condition such as switching operation. The application of static condenser(SC) to prevent the transient voltage instability is introduced.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 한국윤활학회 2002년도 제35회 춘계학술대회
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• pp.169-176
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• 2002

Axial crushing behavior of cylindrical shell Is utilized in the braking of the high-velocity impacting object. In this paper, truncated cone shape brake device is introduced. That is, thickness of the shell is increased gradually from the impacting end to the other end. A detailed experimental investigation on the quasi-static axial crushing behavior of truncated cone type brake devices has been performed. Specimens of various shape were tested to check the influence of design parameters such as length, radius, mean thickness, and conical angle of cylinder. Influence of the material properties were also investigated by adopting aluminum, low carbon steel, and stainless steel as constructing materials. By analyzing deformation procedures of the specimens, it is seen that conical angle influence the deformation mode and the sequence of the wrinkles generation. Braking distance and mean braking force of each specimen were predicted based on the crushing load measured from the tests.

• Journal of Korean Tunnelling and Underground Space Association
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• 제4권2호
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• pp.113-121
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• 2002

This study is focused on establishing influence zone caused by tunnelling in limestone site. Therefore, the numerical analysis using the FLAC2D was performed considering various locations and magnitudes of cavities. To reduce the stress concentration, the shape of cavities was designed to ellipse. This parametric study reveals that the cavities located at crown part and edge part of tunnel greatly have influenced on stability of tunnel. The effect of distance between tunnel and cavity which is larger than 1-0D (Tunnel diameter) dose not directly related to stability of tunnel, but the nearer a cavity location was, the larger displacement and stress of reinforcement occured within 0.25D.

• Journal of Environmental Impact Assessment
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• 제2권1호
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• pp.57-63
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• 1993

An analysis for particle settling effects via of plume centerline tilted exponentially under the influence of panicle settling velocity is carried out for particle of $30{\mu}m$ diameter with $1g/cm^3$ density and 0.02m/s settling velocity corresponding to its particle characteristic according to various wind speeds, atmospheric stabilities. Characteristic analysis of surface concentration distribution simulated by Lagrangian model also are carried out under the influence of plume centerline tilted exponentially at 10m stack height emitted 200 particles per second. This study reveals that plume centerline at the nearby source is sharply tilted exponentially under the condition of stable, weakly wind speed, therefore the lower concentration at the nearby source, the higher concentration at the downwind distance far away from source than actual one is brought out, if not apply the effect of plume centerline tilted exponentially to diffusion Model.

• Journal of Korean Public Health Nursing
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• 제35권3호
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• pp.401-414
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• 2021

Purpose: The purpose of this study was to compare the practice of quarantine guidelines and psychological influence between the young (aged under 64 years) and the elderly (aged over 65 years) groups during the coronavirus disease 19 (COVID-19) pandemic. Method: The data of this study were obtained from the Community Health Survey, 2020, Korean Disease Control and Prevention Agency. A total of 229,296 (young group: 156,314, elderly group: 72,812) participants were included in this study. Independent t-test, chi-square test and descriptive analysis were used for analyzing the data. Result: Elderly group showed lower adherence to wearing face-mask, maintaining social distance when outgoing and practicing handwashing rules than the young group. The elderly group showed a higher level of psychological influence than the young group. In addition, the elderly group had fewer supporters when they were isolated than the young group. Also, the elderly had difficulties in following the quarantine guidelines related to COVID-19. Conclusion: To prevent infection and death from COVID-19 in the elderly, proper education and support programs are needed. Also, support groups should be prepared and applied to relieve their psychological impact related to COVID-19.

• Journal of Korean Tunnelling and Underground Space Association
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• 제14권3호
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• pp.231-246
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• 2012

Recently, the construction of tunnel frequently involves neighboring weak ground conditions. In this case, the stabilized ground could be relaxed by the excavation of tunnel. This will create issues in terms of stability of tunnel. Major factors determining the stability of tunnel can be the direction (angle) of weak zone, the distance between tunnel and boundary of weak zone and so on. In this study, by quantifying the displacement and crack propagation during the excavation of tunnel constructed neighboring weak zone, the influence of the direction of weak zone and the distance between tunnel and boundary of weak zone on the mechanical behavior of tunnel is investigated. A series of experimental scaled model tests by changing the direction of weak zone and the distance between tunnel and boundary of weak zone, are performed and analyzed under the condition of homogeneous material. The results show that as the angle between ground surface and boundary of weak zone moves from horizontal to perpendicular plane, displacement near tunnel increases. An increased distance between tunnel and boundary of weak zone induces displacements near tunnel to decrease and stabilizes beyond a certain level of distance. These findings verify and extend the earlier studies quantitatively. Finally, an appropriate distance between tunnel and boundary of weak zone according to the angle of weak zone is justified. This fundamental insight provides the basis for a more rational design of tunnel neighboring weak ground conditions.

• KSCE Journal of Civil and Environmental Engineering Research
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• 제39권2호
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• pp.273-279
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• 2019

Development of mountain area is increasing due to the demand for improvement of traffic convenience and development of underdeveloped area. Therefore, there frequently are sections where tunnels and interchanges are located close to each other. These sections do not only affect tunnel planning, types and length of interchanges, but also affect more on route selection. In Korea, several design criteria present each reference value but these values are very similar. In the situation, the minimum value among them is usually applied when planning roads and it could cause traffic safety problems in different site conditions. In this study, the problems of design speed, illuminance adaptation distance, and lane change intervals are analyzed by simulating the cases that the problem could occur when calculating the separation distance between tunnel and interchange. The results obtained from this study can be summarized as following: the driving speed should be applied in case that the site has a big gap between design speed and driving speed because the uniform application of the design speed is not safe; the illuminance adaptation distance should include the influence distance in the section affected by the direct light; in addition, the lane change distance should include the time to perceive the situation of the next lane after the lane change in the section required for successive lane change.

• Journal of the Korean GEO-environmental Society
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• 제12권6호
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• pp.25-34
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• 2011

Dredged and reclaimed ground in progress at the West Coast has a high content of coarse particles. There will be different behaviors depending on the location of outlet and engineering properties of soil when its ground is dredged by a pump. Therefore, the experiments were conducted that were manufactured about the chamber equipment of length 2,650mm, width 770mm, height 735mm, experimented step filling method and water content about 300%, 500% and 700% respectively with SM and ML samples in order to realize segregating sediment characteristics of dredged ground with changing much fine. With results of analysis, ML sample by higher initial water content was reached to the period of complete sedimentation and coefficient of sedimentation consolidation increased with increases of diffusion distance. SM samples showed behavior of coarse soil with diffusion distance 120cm, diffusion distance of more than 120cm showed a similar tendency with ML sample under the influence of fines. In ML sample, it could be also found that lower depth and the more increasing diffusion distance increase in percentage of sieve #200 but water content decreases. In SM sample, it could be also found that coarse soil was piled at near the diffusion distance zone but fine soil was piled at the far diffusion distance zone and prominent difference showed between percentage of sieve #200 and water content(%) by boundary point 120cm~160cm of both samples. Also, shear strength was expressed ML-maximum 2.97kPa, SM-maximum 10.2kPa with diffusion distance.