• 대한기계학회논문집B
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• 제31권9호
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• pp.807-813
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• 2007

Recent research on nanofluids under forced convection experiment shows that there is little relationship between convective heat transfer and thermal conductivity increase of nanofluids. This kind of new findings are totally different from the traditional theory of nanofluids, which says that the higher thermal conductivity is a prerequisite for convective heat transfer enhancement. To elucidate this controversial issue in a very comprehensible manner, simple natural convection experiment has been carried out for the water- and oil-based nanofluids. ($water-Al_2O_3$, transformer $oil-Al_2O_3$) Present research shows that there exists strong dependence between natural convection performance and thermal conductivity increase of nanofluids.

• 전기학회논문지P
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• 제58권4호
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• pp.499-504
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• 2009

The analysis for furan compound has provided a complementary technique to dissolved gas analysis(DGA) for monitoring transformers when total concentration of CO and $CO_2$ dissolved in oil only has been evaluated the aging of insulating paper. But, the analysis of furanic compounds by high performance liquid chromatography(HPLC) has been important more than DGA recently. Because it has been known that furanic components in transformer oil have come only from the decomposition of insulating paper. Therefore we have manufactured accelerating aging cell which was aged during 60 hours at 100, 150, 180 and $200^{\circ}C$, respectively, for investigating the characteristics of cellulose paper by thermal using analysis for CO, $CO_2$ and furan compound.

• 전기학회논문지
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• 제63권2호
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• pp.297-305
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• 2014

Nowadays new water supply projects have been on the decline as the water-power constructions have saturated, which means that the existing power equipment have slowly aged and they require more efforts to maintain the system performance. An effective asset management method of power equipment has become a great necessity from both economical and technical aspects. To be balanced, the asset management should look into all three parts: management, engineering, and information. The purpose of this paper is to study a Risk-Based Maintenance (RBM) matrix method through the deterioration evaluation algorithm for an efficient reliability assessment of oil-immersed power transformers by considering both asset management and technical evaluation. Make use of this result, the equipment will be decided to be replace or repair otherwise on service.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 학술대회 논문집 전문대학교육위원
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• pp.48-51
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• 2000

The purpose of this study is to find the way to reduce the electrostatics by interface activation substances added in the insulating oil with concentration[ppm]. As results, The streaming current, surface tension and viscosity of the samples added nonionic and hermaphrodic substances are decreased but the conductivity is increased at higher point than the 1[ppm](c.m.c.), the other side the same phenomena of the samples added cationic and anionic substances are discovered at the 10[ppm].

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1993년도 춘계학술대회 논문집
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• pp.35-38
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• 1993

Pressboard is used for insulation oil-immersed equipment such as transformer. It's low cost, good electrical properties when immersed in oil, ease of storage and installation, and general reliability have made it virtually a universal choice. This study has examined fabricating specimen and specimen characteristics of pressboard.

• 전기학회논문지P
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• 제65권1호
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• pp.41-46
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• 2016

It has been proven that the dissolved gas analysis (DGA) is the most effective and convenient method to diagnose the transformers. The DGA is a simple, inexpensive, and non intrusive technique. Among the various diagnosis methods, IEC 60599 has been widely used in transformer in service. But this method cannot offer accurate diagnosis for all the faults. This paper proposes a fault diagnosis method of oil-filled power transformers using IEC code based neuro-fuzzy model. The proposed method proceeds two steps. First, IEC 60599 method is applied to diagnosis. If IEC code can't determine the fault type, neuro-fuzzy model is applied to effectively classify the fault type. To demonstrate the validity of the proposed method, experiment is performed and its results are illustrated.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 C
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• pp.1478-1480
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• 1997

We investigated the breakdown characteristic of mineral oil according to applied voltage and tip radius. In this experiment, electrode system was point-plane geometry. The tip radius of needle was 5, 10, 20 and $25{\mu}m$, respectively. Applied voltage was AC and DC. We measured breakdown voltage for each tip radius with increasing electrode gap, 2mm to 10mm. Under nonuniform electric field, breakdown strength was higher when needle was negative than when needle was positive. Because it is polarity effects due to space charge. And the more sharp tip radius, whether we applied AC or DC, the higher breakdown strength. As tip radius increase, breakdown strength decreases exponentially.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 추계학술대회 논문집 전기물성,응용부문
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• pp.183-186
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• 2002

It is well known that a discharge in oil is the source of various physical and chemical phenomena. One of them is ultra-sonic wave, and its detection is a useful method to the diagnosis of the transformer insulation condition. Conventionally, ultra-sonic waves are detected by Piezo-electric trans-ducer(PZT), and we use optical method that has many advantages. In this paper, we constructed a Mach-Zehnder interferometer with optical fiber and investigated the principle of operation. Test of the ultrasonic-detecting ability was performed for both of PZT and fiber-optic sensor. Discharge test arrangement is based on the needle-plane electrode system in oil and applied AC high voltage. Ultrasonic waves were detected and showed time-delay characteristics. We analyzed the data with frequency domain and wavelet transform.

• 대한화학회지
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• 제43권3호
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• pp.286-293
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• 1999

변압기 오일에 함유되어 있는 폴리염화바이페닐(PCB)의 제거를 위해서 화학적 처리와 제어된 산화반응에 의한 열적처리를 상호 결합시킨 한 포괄적인 공정이 이루어 졌다. 화학시약을 이용한 화학처리에서 완전히 처분할 수 없었던 폴리염화바이페닐은 오일의 순환중 에 적절한 흡착제로 걸러진 후 열처리되었다. 열처리에 의해서 폴리염화바이페닐은 99.99% 이상 파괴 되었으며 독성 부산물인 PCDDs나 PCDFs는 처리과정 중에 형성되지 않았다. 변압기에 있는 오일이나 무기지지체는 공정 후에 재회복 되었다. 화학 및 열적처리를 결합시킨 이 공정은 환경적으로 유익하며, 다른 유용한 기술보다도 사용하기 쉽고 효과적이며 경제적 이었다.

• 한국조명전기설비학회지:조명전기설비
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• 제11권2호
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• pp.110-118
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• 1997

본 논문은 DSP를 이용한 주상변압기 유전정접($tan\;delta$) 활선 측정기법을 제안하였다. 변압기 내부에 콘덴서를 삽입한 후 센서에 전압을 인가하고, 인가된 전압과 콘덴서에 흐르는 전류를 측정하여 본 논문에서 제안한 상호 상관 함수 기법을 이용하여 유전정접을 구하였다. 측정의 성능 향상을 위해 TMS320C31 DSP 보드를 사용하였으며 상호 상관 함수 기법을 사용하였다. 또한 노이즈 영향을 검토하기 위해 컴퓨터 시뮬레이션을 수행하였다. 본 연구의 검증을 위해 본 논문에서 구현한 측정장치와 Schering bridge을 사용하여 비고 실험을 하였다. 실험 결과 주상 변압기 절연진단에 충분히 활용할 수 있음을 알 수 있었다.