• 비파괴검사학회지
• /
• 제16권3호
• /
• pp.155-161
• /
• 1996

회전 기계의 저어널 베어링 상태를 음향 방출(AE) 기술을 활용하여 감시하기 위한 진단 시스템을 개발하였다. AE 기술은 베어링 시스템에 있어서 비정상 상태를 탐지하기 위하여 이용된다 모의 저어널 베어링시스템을 이용한 실험과 실제 발전 설비에 대한 적용 시험의 결과로부터 AE 신호 파라메타 중에서 rms voltage가 가장 유효한 것으로 판명되었으며, 이러한 연구 결과를 토대로 하여 진단 시스템의 알고리즘과 판단 기준들이 설정되었다. 베어링 진단 시스템은 AE 센서 및 전치앰프로 구성된 신호 감지부, AE rms voltage를 측정하기 위한 rms-to-DC 변환 회로부로 구성된 신호 처리부, A/D 변환기를 이용하여 rms voltage 신호를 PC에 연결해 주는 인터페이스부, 베어링 상태 보기와 진단 프로그램을 포함하는 그래픽 디스플레이 및 소프트웨어부의 4부분으로 구성된다.

• Journal of Biosystems Engineering
• /
• 제38권2호
• /
• pp.113-120
• /
• 2013

Purpose: Stem cells provide new opportunities in the regenerative medicine for human or animal tissue regeneration. In this study, we report an efficient method for the modulating behaviors of electro-active stem cells by micro-electric current stimulation (mES) without using chemical agents, such as serum or induction chemicals. Methods: Dental pulp stem cells (DPSCs) were cultured on the tissue culture dish in the mES system. To find a suitable mES condition to promote the DPSC functions, the response surface analysis was used. Results: We found that a working micro-current of 38 ${\mu}A$ showed higher DPSC proliferation compared with other working conditions. The mES altered the expressions of intracellular and extracellular proteins compared to those in unstimulated cells. The mES with 38 ${\mu}A$ significantly increased osteogenesis of DPSCs compared with ones without mES. Conclusions: Our findings indicate that mES may induce DPSC proliferation and differentiation, resulting in applying to DPSCs-based human or animal tissue regeneration.

• 전력전자학회논문지
• /
• 제3권1호
• /
• pp.1-7
• /
• 1998

발전설비의 대형화로 인하여 전력절감 문제가 크게 대두되었고, 팬이나 펌프를 부하 변화에 따라 속도제어하므로써 전기 에너지를 절약 할 수 있다. 1MVA급 단위 인버터 2대를 병렬 운전하여 대용량 2MVA GTO 인버터를 구현하였으며, 단위 인버터의 병렬 운전은 2대의 출력변압기 2차측 결선을 직렬 연결하여 구현하였다. 개발된 시스템은 제어반, 정류기반, 2대의 인버터반으로 구성되어 있으며, 이 시스템은 한국전력공사 성인천복합화력발전처 해수펌프 구동 유도전동기(6.6KV 1500KW)에 적용되어 전력절감에 기여하고 있다. 또 단위 인버터가 상호 180$^{\circ}$위상차를 갖도록 병렬 운전하므로써 고조파 성분을 저감시키면서 대용량을 구현하였다.

• 폴리머
• /
• 제36권4호
• /
• pp.494-499
• /
• 2012

본 연구에서는 다중벽 탄소나노튜브(MWCNT)의 함량을 1에서 10 wt%까지 달리하여 MWCNT 강화 폴리프로필렌(PP) 나노복합재료의 전자파 차폐효과 및 기계적 특성에 미치는 영향에 대해서 살펴보았다. 전기전도도는 4단자법으로 측정하였고, 전자파 차폐효과는 흡수와 반사방법으로 분석하였다. 기계적 특성은 임계응력세기인자($K_{IC}$) 측정을 통하여 고찰하였으며, 모폴로지는 주사전자현미경(SEM)으로 관찰하였다. 실험결과, MWCNT의 함량이 증가함에 따라 차폐효과가 향상됨을 확인할 수 있었으며, MWCNT의 함량이 전자파 차폐효과를 결정하는 중요한 요소임을 알 수 있었다. $K_{IC}$값도 MWCNT의 함량이 증가할수록 큰 값을 가지는 것을 확인할 수 있었으나 5 wt% 이상에서는 오히려 감소하였다. 이는 과량의 MWCNT가 PP 내에서 서로 뭉침으로 인하여 $K_{IC}$값을 감소시킨 것으로 판단된다.

• Journal of Biosystems Engineering
• /
• 제9권2호
• /
• pp.65-73
• /
• 1984

While most of researches on the performance of high temperature grain dryer have dealt mainly with improving dryer capacity and drying speed during the last twenty years, energy efficiency, in fact, has not been emphasized. Current fuel supplies and energy cost have shifted the emphasis to reducing the energy consumption for grain drying while maintaining dryer capacity and grain quality. Since the energy input for drying is relatively large, the recovery and reuse of at least part of the exhaust energy can significantly reduce the total energy consumption in existing drying systems. Unilization of exhaust heat in grain dryer either through direct recycling or by a thermal coupling in heat exchanger have been subject of a number of investigators. However, very seldom research in Korea has been done in this area. Three drying tests(non-recycling, 0.22 recycle ratio, and 0.76 recycle ratio)were performed to investigate the thermal efficiency and heat loss factors of continuous flow type dryer, and to analyze the effect of recycle ratio (weight of exhaust air recycled/total weight of input air) on the energy requriements for rough rice drying. The test results showed that when the exhaust air was not recycled, the energy lost from furnace was 15.3 percent of input fuel energy, and latent and sensible heat of exhaust air were 61.4 percent and 11.2 percent respectively. The heat which was required in raising grain temperature and stored in dryer was relatively small. As the recycle ratio of exhaust air was increased, the drying rate was suddenly decreased, and thermal efficiency of the kerosene burner was also decreased. Drying test with 0.76 recycle ratio resulted in 12.4% increase in fuel consumption, and 38.4% increase in electric power consumption as compared to the non-recycled drying test. Drying test of 0.22 recycle ratio resulted in 6.8% saving in total energy consumption, 8.0% reduction in fuel consumption, and 2.5% increase in electric power consumption as compared to the non-recycled drying test.

• 한국재료학회지
• /
• 제12권7호
• /
• pp.573-579
• /
• 2002

Stoichiometric mullite ($3Al_2$$O_3$. $2SiO_2$) precursor sol has been prepared by sol-gel method. The effects of the precursor pH and sintering temperature on the synthesizing behavior and morphology of mullite have been studied. Mullite precursor sol was prepared by dissolution of aluminum nitrate enneahydrate (Al($NO_3$)$_3$.9H$_2O) into the mixture of silica sol. Precursor pH of the sols was controlled to acidic condition ($PH\leq$ 1~1.5) and to basic condition ($pH\geq$8.5~9). The synthesized aluminosilicate sols were formed under 20 MPa pressure after drying at $150^{\circ}C$ for 24 hours, and then sintered for 3hours in the temperature range of $1100~1600^{\circ}C$. From TGA/DTA analysis, total weight loss in the aluminosilicate gel of the acidic sample was (equation omitted) 56% and that of the basic sample was (equation omitted) 85%, indicating that the synthesizing temperature of mullite phase for acidic and basic samples was above $1200^{\circ}C$ and $1300^{\circ}C$, respectively. The morphologies of the synthesized mullite were fine and needle-like (or rod-like) for acidic sample, and granular for basic sample that has been sintered above $1300^{\circ}C$. It was found that the morphology of mullite particle was predominantly governed by precursor pH and sintering temperature.

• 한국인터넷방송통신학회논문지
• /
• 제18권6호
• /
• pp.187-193
• /
• 2018

국내에서의 전력에 대한 수요는 점진적으로 증가하고 있는 추세이다. 수요에 대응하기 위한 발전소는 기능이 다양해지고 효율이 점차 커져야 한다. 발전소 내의 전력 기기에서 사고가 발생하면 막대한 경제적 손실 및 장애를 초래하게 된다. 사고 발생의 원인 중의 하나로서 절연 성능이 저하 된 케이블이 있다. 케이블 사고를 미연에 방지하기 위하여 절연의 상태를 감시하고 확인하여야 한다. 케이블 사고는 연결 부위인 접속에서 발생하는 사고가 대부분을 차지한다. 본 연구와 관련하여 우리는 접속부 상태를 판별하기 위한 장비를 개발하였고, 한국서부발전(주)의 현장에 설치하여 운용 중이다. 본 논문에서는 현장에서 설치 운용 중인 장비에 대한 설명과 더불어 설치 운용된 결과를 통해 케이블의 수명을 예측할 수 있는 고전압 케이블 접속재의 안정적 사용을 위한 온라인 감시진단기법 중에서 사고가 가장 빈번하게 발생하는 접속부에 대해 안정적인 사용을 위한 진단의 정확성과 신뢰성을 향상시키기 위한 연구를 하였다. 이 논문에서 하드웨어 구성을 위주로 우리가 개발한 장비를 소개한다.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2002년도 하계학술대회 논문집 B
• /
• pp.1361-1363
• /
• 2002

Micro-SMES(Superconducting Magnetic Energy Storage) has been studied as an impulsive high power supply for industrial applications. Recently, electric power reliability of our country has been improved. However, there are still remaining problems which are short-duration variations like instantaneous and momentary interruption and voltage sag by nature calamity ; typhoon, lightning, snow, etc. Besides, power quality ; harmonics, goes down because of using power electronics equipments. Malfunction of controller and stop machinery, and losing important data are caused by poor power quality at a couple of second in accuracy controllers. Due to those, battery based UPS has been used, but there are several disadvantages ; long charge and discharge time, environmental problem by acid and heavy metal, and short life time. Micro-SMES is an alternative to settle problems mentioned above. However, there need huge system apparatuses in order to verify the effect of system efficiency and stability considering the size of micro-SMES, the sort of converter type, and various conditions. This paper presents a cost effective simulation method of micro-SMES and power converter, and design for micro-SMES based system using PSCAD/EMTDC.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1995년도 하계학술대회 논문집 C
• /
• pp.1394-1397
• /
• 1995

In the hazardous areas where explosive gases, vapor or mists exist, electrical apparatus and installations must be of explosion-proof construction to prevent or limit the danger of the ignition of potentially explosive atmosphere. In Korea, nine types of protection have been specified in the government regulations at present: flameproof enclosure, pressurization, oil immersion, increased safety, intrinsic safety, non-incendive, sand filling, encapsulation, and special types. Among these types, the intrinsic safety has the construction which limit or by-pass igniting the electric energy using electronic devices. This type has lots of merits but at the same time requires a high-degree of technology. In this paper, we investigated several dominating factors which affect the minimum ignition energy: this energy plays a very important role in design and evaluation of the intrinsic safety type electrical apparatus. Eletrode material, which is one of the most important factors, was intensively studied for the five sorts of material(Al, Cd, Mg, Sn, and Zn) with performing experiment in a low-voltage inductive circuit using IEC-type spark apparatus. The experimental results show that the minimum ignition energy of electrode material is varied: highest in Cd and lowest in Sn. We also confirmed the effect of eletrode make-and-break speed and magnetic field magnitude.

• Journal of Biosystems Engineering
• /
• 제30권1호
• /
• pp.32-37
• /
• 2005

This study was conducted the slurry pig manure treatment by condensation drying of liquid from the slurry manure with a heat-pump and electric heater combined with air flow channel system. The system was designed as liquid and solid matters separation of slurry manure, and it can doing continuous input of slurry manure from a pig house, and it can operated year round use for pig farms. The separation of liquid and solid matters from slurry manure needed the prevention of solid accumulation in the system. The system was designed as closed space from outside air space for maximized evaporation of liquid and the condensation of liquid from slurry manure. The system can be operated the pig slurry manure treatment regardless of seasons in a yew. The separated evaporation water from the pig slurry manure by the heat-pump was satisfactorily pure water that can be used as washing water in livestock farms. The system can applicate to about 100 heads of pig, and the proper area of evaporation plate system was considered around $10\;m^2$. The input electrical energy of about 15 kWh which the cost equal to 250,000 won per month.