• 한국전기전자재료학회논문지
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• 제16권6호
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• pp.490-495
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• 2003

The electromagnetic properties and thermal behavior of Mn-Zn ferrite cores for the blocking filter of Power Line Communication(PLC) application were investigated as a function of additives. The highest density and permeability were 4.98 g/$\textrm{cm}^2$ and 8,221, respectively and were obtained to the specimen with composition of MnO 24 mol%, ZnO 25 mol% and Fe$_2$O$_3$ mol%, added MoO$_3$ of 400 ppm, SiO$_2$ of 100 ppm, and CaO of 200 ppm. The uniform grains were organized, and the microstructures were densified due to reduction of pores in the specimen. The permeability was increased up to 13,904 as the temperature of specimen increased to 110$^{\circ}C$. However, it was decreased precipitously under 100 over 110$^{\circ}C$. The exothermic behavior was observed in the frequency range from 1 kHz to 1 MHz, and the maximum temperature of specimen was 102$^{\circ}C$ at 1 MHz. In the consequence, the Mn-Zn ferrite core developed in this research will maintain the stable electromagnetic properties since the temperature of ferrite core rose to 93$^{\circ}C$ in the range of 100 kHz to 450 kHz bandwidth qualified for PLC. The blocking filters were designed for single phase and three phases using the in-line and non-contact core. The best attenuation ratios of -46.46 dB and -73.9 dB were measured in the range of 100 kHz to 450 kHz bandwidth, respectively.

• KEPCO Journal on Electric Power and Energy
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• 제2권3호
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• pp.383-389
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• 2016

국내 154 kV 복도체 가공송전선로를 대상으로 전자력에 의한 소도체간 접촉현상을 실증적으로 재현하고 대처 방안을 제시하였다. 도체에 흐르는 전류의 크기가 클수록, 스페이서의 간격이 클수록 소도체간에 작용하는 전자력은 크게 측정되었다. 스페이서 간격이 68 m일 경우 전류 크기가 2,000 A 일 때부터 소도체는 불안정한 상태가 되어 소도체간 간격이 변화하는 횡방향 진동이 시작되었다. 스페이서 간격이 136 m일 경우 전류 크기가 증가할수록 소도체간 간격은 좁아지다가 2,250 A 일 때 두 소도체는 완전히 접촉하였다. 스페이서 간격에 따른 전자력의 크기를 도식화하고 안전한 스페이서 간격을 제시하였다. 시험선로와 실선로 간에는 접촉현상이 발생하는 조건이 상이한 것으로 나타났으며, 이는 송전선로 가선 과정에서 도체에 가해진 여러 형태의 잔류 응력, 바람 조건 등의 차이 때문으로 판단되었다.

• 한국운동역학회지
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• 제27권4호
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• pp.239-245
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• 2017

Objective: The bobsleigh shoes used in the start section are one of the most important equipment for improving the competition. Despite the importance of the start section, there are no shoes that are specific for bobsleigh athletes in Korea and Korean athletes have to wear sprint spike shoes and practice the start instead of wearing bobsleigh shoes. The objective of the present study was to provide data for improving the performance of Korean bobsleigh athletes by investigating the differences in their split time, plantar pressure, and forefoot bending angle based on skill levels at the start of a run under the same conditions as training conditions. Method: Six Korean bobsleigh athletes were divided into two groups, superior (n=3) and non-superior (n=3). A digital speedometer measured the split time at the start; the Pedar-X system (Novel, Germany) measured plantar pressure. Plantar pressures and split times were measured as the athletes pushed a bobsleigh and sprinted at full speed from the start line to the 10-m mark on the bobsleigh track. An ultra-high-speed camera was used to measure the forefoot bending angle during the start phase. Results: Significant between-group differences were found in split times (p<.000; superior = 2.38 s, non-superior = 2.52 s). The superior group had a larger rearfoot (p<.05) contact area, maximum rearfoot force (p<.01), and a larger change in angles 3 and 4 (p<.05). Conclusion: At the start of a bobsleigh run, proper use of the rearfoot for achieving effective driving force and increasing frictional resistance through a wider frictional force can shorten start time.