• Proceedings of the KIEE Conference
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• 1998.07e
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• pp.1746-1748
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• 1998

In this paper, the relation between the increment of metallic content such as copper(Cu) and iron(Fe) according to degradation of pole-transformer oil and change of electrical characteristics according to increment of metallic content was studied. As the result, electrical characteristics was decrease according to increment of metallic content, especially copper content, and the trend of T.C.G(Total Carbonic Gas) agreed with the trend of copper content.

• Proceedings of the KIEE Conference
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• 1997.07e
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• pp.1696-1701
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• 1997

본 연구에서 사용된 절연유 열화센서는 주 매질이 기공 세라믹(Porous Ceramic)으로 구성되어 있어 열화생성된 유불용성분(油不溶 成分)이 일정 크기의 기공 속을 통과할 때 절연유의 열화정도에 따라 인위적인 도전 통로가 형성되는 데, 이러한 회로를 이용하여 전기적인 분석으로 측정된 센서의 누설전류치와 기존 실시되고 있는 절연유 분석법인 전산가, 내압치와 상호 비교 분석한 결과, 지금까지 샘플링에 의한 화학적인 분석법에 앞서 전기적인 분석법으로 절연유 열화 상태를 간단하게 분석할 수 있다는 가능성을 제시하였다.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.57 no.2
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• pp.176-180
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• 2008

A field-oriented UHF system for on-line PD monitoring of transformers is designed, which has been installed inside the oil tank of transformer in a substation by two ways: on-line installing mode through the oil-valve and pre-installing mode through the man hole/hand hole cover. This system has successfully captured long intermittent discharge signals that hadn't been detected through conventional techniques, and solved the problem successfully. The results demonstrate that UHF technique has great advantages for on-line PD monitoring of transformers. By adopting the peak detection technique, it becomes easy and effective for the transplantation of the phase-resolved pattern recognition technique from conventional method to UHF method, and then to realize continuous on-line monitoring, source characterization and trending analysis.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.43 no.3
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• pp.432-436
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• 1994

The aging characteristics of amorphous FeS178TBS113TSiS19T wound cores have been investigated as a function of aging temperature and time. The core losses(1.2T/60Hz) of amorphous wound cores dipped in transformer oil decrease in comparision with initial stage of aging test due to insulation of ribbon stacks by oil penetration. It is estimated that it takes 30 years or more for 10% increase in core losses (1.2T/60Hz) of amorphous wound cores aged at normal transformer running temperature(100$^{\circ}C$). So we condlude that the amorphous core is satisfactorily applicable to transformer.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1903-1905
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• 2000

Power transformers have a tendency of ultra-high voltage capacity as power demand increases day after day KEPCO also will have plan to supply transmission power from 345KV to 765KV in the early of 2000. Therefore, the fault by insulation destruction gives rise to large area of power failure in huge capacity transformers. On-line predictive diagnostics is very important in power transformers because of economic loss and its spreading effect. This study presents the algorithm for transformer oil analysis used KEPCO code, IEC code, gas pattern method and Dornenburg & Roger Ratio method. We also describe the MMI display of expert system programmed by Element Expert Tool(Neuron Data Inc.).

• Transactions on Electrical and Electronic Materials
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• v.13 no.5
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• pp.229-232
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• 2012

DGA is one of the most recent techniques developed to diagnose the fault condition on oil filled insulation transformers. There are more than 6 known different methods of DGA fault interpretation technique and so there is the likelihood that they may vary in their interpretations. A series of combined interpretation methods that can determine the power transformer condition faults in one assessment is therefore needed. This paper presents a computer program- based system developed to combine four DGA assessment techniques; Rogers Ratio Method, IEC Basic Ratio Method, Duval Triangle method and Key Gas Method. An easy to use Graphic User Interface was designed to give a visual display of the four techniques. The result shows that this assessment method can increase the accuracy of DGA methods by up to 20% and the no prediction result had been reduced down to 0%.

• Proceedings of the KIEE Conference
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• 1999.11d
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• pp.897-899
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• 1999

In this paper, the interfacial dielectric breakdown phenomenon of interface between Epoxy/EPDM (ethylene propylene diene terpolymer) was discussed, which affects stability of insulation system of power delivery devices. Specimen structure was designed by using MAGSOFT's FLUX2D based on the finite elements method. Design concepts is to reduce the effect of charge transport from electrode in the process of breakdown and to have the tangential electrical potential with the Epoxy/EPDM interface. AC interfacial breakdown phenomenon of was investigated by variation of interfacial conditions oil and temperature which are supposed to have influence on the interfacial breakdown strength. Interfacial breakdown strength was improved by spreading oil over interfacial surface. The decreasing ratio of the AC interfacial breakdown strength in non-oiled specimens was increased by the temperature rising and its of oiled specimens was not affected by temperature.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.52 no.3
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• pp.257-262
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• 2016

Flexible two-phase thermosyphons are devices that can transfer large amounts of heat flux with boiling and condensation of working fluid resulting from small temperature differences. A flexible two-phase thermosyphon consists of a evaporator, an insulation unit, and a condenser. The working fluid inside the evaporator is evaporated by heating the evaporator in the lower part of the flexible two-phase thermosyphon and the evaporated steam rises to the condenser in the upper part to transfer heat in response to the cooling fluid outside the tube. The resultant condensed working fluid flows downward along the inside surface of the tube due to gravity. These processes form a cycle. Using R134a refrigerant as the working fluid of a loop type flexible two-phase thermosyphon heat exchanger, an experiment was conducted to analyse changes in boiling heat transfer performances according to differences in the temperature of the oil for heating of the evaporator, the temperature variations of the refrigerant, and the mass flows. According to the results of the present study, the circulation rate of the refrigerant increased and the pressure in the evaporator also increased proportionally as the temperature of the oil in the evaporator increased. In addition, the heat transfer rate of the boiler increased as the temperature of the oil in the evaporator increased.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.254-257
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• 1997

In this paper, we investigated the effects of gap length and tip radius influenced in breakdown of mineral based insulation oil Electrode system was needle-plane geometry It is to model conductive extrusions in oil filled electrical power apparatus. The tip radius of needle electrode was 5, 10, 20 and 25${\mu}{\textrm}{m}$, respectively. We measured breakdown voltage for each of tip radius with increasing electrode gap, 2mm to 12mm. It was calculated electrical breakdown strength at tip using Mason\`s equation from breakdown voltage As gap lenght increased. breakdown strength increased linearly. But, as tip radius of needle increased, breakdown strength decreased exponentially. It can be explained by tole phenomenon that electron is easily injected, as tip radius increases, and effective work function decreases. When appling DC voltage. breakdown 7tr7ilgtll was higher wheal polarity of needle was negative than positive. It is because of the space charge effect ill accordance with the influence of liquid motion.

• Journal of the Korean Society of Safety
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• v.19 no.1
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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.