• 한국안전학회지
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• 제19권1호
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• pp.56-59
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• 2004

In this paper, we investigated the influence of gap length and tip radius on breakdown of mineral based insulation oil. Applied voltages were DC and AC voltage. Electrode system was needle-plane structure. The tip radius of needle electrode was 5, 10, 20 and 25${\mu}m$, respectively. We measured breakdown voltage for each of tip radius with increasing electrode gap, 2mm to 12mm. Electric breakdown strength at tip was calculated using Mason's equation contained geometric figure. As gap length increased, breakdown strength increased linearly. But, as tip radius of needle increased, breakdown strength decreased exponentially. It can be explained by the phenomenon that electron is easily injected, as tip radius increases, and effective work function decreases. When appling DC voltage, breakdown strength was higher when polarity of needle was negative than positive. It is because of the space charge effect in accordance with the influence of liquid motion.

• 전기학회논문지P
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• 제60권3호
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• pp.114-119
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• 2011

Large Power transformer is a complex and critical component of power plant and consists of cellulosic paper, insulation oil, core, coil etc. Insulation materials of transformer and related equipment break down to liberate dissolved gas due to corona, partial discharge, pyrolysis or thermal decomposition. The dissolved gas kinds can be related to the type of electrical faults, and the rate of gas generation can indicate the severity of the fault. The identities of gases being generated are using very useful to decide the condition of transformation status. Therefore dissolved gas analysis is one of the best condition monitoring methods for power transformer. Also, on-line multi-gas analyzer has been developed and installed to monitor the condition of critical transformers. Rogers method, IEC method, key gas method and Duval Triangle method are used to failure diagnosis typically, and those methods are using the ratio or kinds of dissolved gas to evaluate the condition of transformer. This paper analyzes the reliability of transformer diagnostic methods considering actual dissolved gas concentration. Fault diagnosis is performed based on the dissolved gas of five transformers which experienced various fault respectively in the field, and the diagnosis result is compared with the actual off-line fault analysis. In this comparison result, Diagnostic methods using dissolved gas ratio like Rogers method, IEC method are sometimes fall outside the ratio code and no diagnosis but Duval triangle method and Key gas method is correct comparatively.

• 분석과학
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• 제18권5호
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• pp.410-418
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• 2005

PCBs는 뛰어난 물리 화학적, 열적 안전성과 전기 절연성으로 인해 윤활유, 열교환유체, 복사지 등 많은 용도로 사용되어 왔으며, 1930년대에서 1970년대까지 Aroclors, Kaneclors, Clophens, Phenaclors 등과 같은 상업적 PCBs 생산품들이 절연유로 사용되었다. 본 연구에서는 PCBs의 주된 배출원인 변압기 절연유를 채취하여 Aroclor 1242, 1248, 1254, 1260의 표준물질을 사용하여 정성분석을 하였다. 제작년도 및 제작사별로 채취 분석한 결과 절연유는 Aroclor 1242, Aroclor 1254, Aroclor 1260의 단일 제품을 함유하거나 이들이 혼합되어 함유되어 있는 것으로 조사되었다. 또한, 시판되는 스크리닝 키트(20 ppm, 50 ppm)를 이용한 절연유 시료 분석방법의 적용성을 검토하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 추계학술대회 논문집 Vol.15
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• pp.51-54
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• 2002

폴리머 애자용 Shed 재료의 전기방전에 대한 열화내성과 표면발수성은 제품의 장기성능에 있어서 가장 중요한 물성들이다. 그러나 무기보강재의 첨가량이 많아 무결점 성형성을 만족하도록 하기 위해서 Process Oil의 사용이 불가피한데 사용하는 오일의 종류와 양에 따라 옥외절연물의 장기성능에 영향을 주는 표면발수성이나 방전내성은 크게 차이가 나는 것으로 밝혀져 있다. 본 논문에서는 화학적 구조와 점도가 다른 몇 종의 hydroxy silicone oil(HS 오일)을 혼련 (kneading) 하는 과정에 첨가하여 이들 오일의 종류와 양이 고무의 기본적인 물성, 발수성, 방전열화내성， 내트래킹성 등에 어떻게 영향을 주는가를 조사하였다. 코로나 처리시간에 따라서 접촉각의 저하정도와 코로나 처리 후 경과시간에 따른 발수성의 회복특성을 조사하였다. HS 오일의 접도에 따라 초기발수성, 발수성 회복특성의 차이가 많았다. 점도가 낮을수록 초기 발수성 저하는 크며 회복속도는 빠른 반면 점도가 높을수록 초기 발수성 저하는 작은 반변은 발수성 회복속도는 다소 느리게 나타났다 내트래킹성 결과는 점도가 높을수록 우수한 특성을 보였다. 결론적으로 폴리머 애자용 실리콘고무의 컴파운딩에서 실리콘오일의 선택은 성형작업성, 발수성회복특성, 열화내성 외에 가격 등을 고려하여 최적화가 필요하다.

• 전기학회논문지
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• 제59권5호
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• pp.939-944
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• 2010

A high voltage air-cored helical strip/wire type pulse transformer has been fabricated for charging of a high voltage pulse forming line. As a primary coil, copper strip of 25mm width was wound helically around a MC nylon cylinder. For a secondary coil, copper enameled wire of 1mm diameter was wound around conical cylinder in order to provide insulation between two windings. The coupling coefficient of 0.53 was obtained when two coils were combined coaxially in the insulation oil filled chamber. Voltage gain and energy transfer efficiency were investigated by varying the parameters of primary and secondary circuit. Test results shows that the voltage gain increases up to 17 with increasing the primary capacitance up to 200nF. And highest energy transfer efficiency of 44% was obtained when the dual resonant operation condition was nearly satisfied. The pulse transformer developed in this study can be used for charging the middle conductor of a Blumlein pulse forming line.

• 조명전기설비학회논문지
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• 제23권11호
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• pp.52-60
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• 2009

High reliability is essential for power transformers, and their fault causes are reportedly more related to mechanical causes than electrical ones. The transformer soundness judgment currently depends only on the electrical insulation characteristic and the chemical test of the insulation oil, so that there are few fundamental measures against the frequent mechanical damages and failures in transformers. The mechanical soundness judgment techniques are conducted through processes that include structural analysis and vibration resistance treatment during the manufacturing process of each manufacturer, but the vibration is not tested during the design, manufacturing, and operating processes since there are no detailed technical standards and procedures on the vibration problem, which are important in terms of maintenance. Therefore, in this study, vibration phenomena were measured from the 32 power transformers in operation in the substations under the Daejeon Power Transmission District Office of the Korean Electric Power Corporation (KEPCO). The vibration was measured at 24 sections ($6{\times}4$) on one side, and only the maximum values were selected from the measured vibration values. This was because the maximum vibration values more significantly affect the soundness of the transformer than the average vibration values. The vibration classes were given considering the maximum vibration based on ISO 10016-1 (2001).

• Transactions on Electrical and Electronic Materials
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• 제8권6호
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• pp.278-282
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• 2007

In the complex insulation system that is used in extra high voltage(EHV) devices, according to the trend for electric power equipment of high capacity and reduction of its size, macro interfaces between two different bulk materials which affect the stability of insulation system exist inevitably. In this paper, the dielectric strength decrease of the macro interfaces between epoxy and ethylene propylene diene terpolymer(EPDM) was estimated by using the applied voltage to breakdown time characteristics. Firstly, the AC short time dielectric strength of specimens was measured at room temperature. Then, the breakdown time was measured under the applied constant voltage which is 70% of short time breakdown voltage. With these processes, the life exponent n was determined by inverse power law, and the long time breakdown voltage can be evaluated. The best condition of the interface was LOS(low viscosity(350 cSt) silicone oil spread specimen). When 30 years last on the specimens, the breakdown voltage was estimated 44% of the short time breakdown voltage.

• 한국안전학회지
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• 제32권6호
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• pp.22-28
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• 2017

According to the National Fire Data System (NFDS), more than 5,000 vehicle fires have occurred every year for the last 10 years. Vehicle fires are primarily caused by mechanical (breaking system and engine), electrical (wiring and battery), and chemical (oil and fuel gas leakage) problems. The electrical factor has increased with the installation of driver convenience equipment. For example, today, the black box is widely used to provide video data recording of motor vehicle accidents. The black box consists of a front camera, rear camera, and wires. The black box wires are directly connected to the junction box or fuse box from the start battery that operates to provide normal on power supplying for engine stop. It is extremely dangerous when the wires short circuit due to insulation aging, mechanical and electrical stress, etc. In this study, the black box wiring fire risk have been analyzed and investigated when the steady state and abnormal operations, and under the following conditions: wiring arrangements with a high temperature condition, insulation aging, poor contact, and short circuits. The results showed that black box wiring short circuits had a higher fire risk than the other fire hazard elements. To prevent fire hazards caused by black box wiring, the black boxes must be installed by qualified service personnel. Do not modify the wiring, remove the fuse and secure the wiring using cable ties or insulation tape.

• 조명전기설비학회논문지
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• 제21권1호
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• pp.104-110
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• 2007

본 논문은 권선내부에 온도계가 설치된 지상변압기를 제작하여 부하운전에 따른 배전용 변압기의 온도상승 특성과 절연유의 유전특성 변화를 관찰하였다. 관찰결과 배전용변압기의 경우 과열점은 세 권선 중 두개의 권선이 접하고 권선의 약 2/3 높이에 위치하고 있으며, 과열점과 절연유 상부 간에 약 $17[^{\circ}C]$의 일정한 온도차를 확인할 수 있었다. 또한 절연유의 정전용량특성은 온도와 선형적인 관계로 감소하는 특성을 보이며, 그 기울기는 열화율과 무관하게 -0.0106의 일정한 값을 관찰할 수 있었다. 이 결과는 수명손실의 정확한 계산과 열화진단을 위한 기구로 활용할 수 있을 것이다.

• Journal of Advanced Marine Engineering and Technology
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• 제39권4호
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• pp.449-455
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• 2015

전력용 변압기 용량의 증대와 고효율화에 따른 권선의 단위체적당 열발생량의 증가 및 이에 따른 절연성능의 저하는 전력용 변압기의 수명과 신뢰성에 큰 영향을 준다. 이러한 문제점은 방열기의 냉각성능을 증가시킴으로써 해결이 가능하다. 본 연구는 ONAF(Oil Natural Air Forced) 형식의 변압기의 방열기에 대해 공기의 강제대류를 일으키는 팬의 위치에 따른 냉각성능 평가를 통하여 냉각효과가 가장 큰 팬의 위치를 찾기 위한 것이다. 해석에는 유동해석 상용소프트웨어를 사용하였으며, 해석시간의 단축을 위하여 오일의 냉각유로를 단순화시켰고 팬의 지름을 일정하게 두고 팬의 위치를 다양하게 변화시켜가며 해석을 실행하였다. 해석 결과 팬의 수직적인 위치 변화는 냉각성능에 크게 영향을 주지 않았으나 팬이 변압기의 전방영역에 위치할 경우 후방영역의 배치보다 온도강하가 큰 것을 확인할 수 있었다.