• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1552-1553
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• 2011

The HVDC transformer which is one of the main equipments for HVDC(High Voltage Direct Current) electric power transmission systems is exposed to not only AC voltage but also the inflowing DC voltage which comes from the DC-AC converter systems. Therefore, the HVDC transformer insulation system is required to withstand the electric field stress under AC, DC and DC polarity reversal conditions. However the electric field distributions under those conditions are different because the AC electric field and DC electric field are governed by permittivity and conductivity, respectively. In this study, the changes of electric potential and electric field of conventional AC transformer insulation system under DC polarity reversal test condition were analyzed by FEM(Finite Element Method). The DC electric field stress was concentrated in the solid insulators while the AC electric field stress was concentrated in the mineral oil. In addition, the electric stress under that condition which is affected by the surface charge accumulation at the interfaces between insulators was evaluated. The stress in some parts could be higher than that of AC and DC condition, during polarity reversal test. The result of this study would be helpful for the HVDC transformer insulation system design.

• Proceedings of the KIEE Conference
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• 2004.05b
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• pp.35-38
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• 2004

본 연구는 국내에서 사용되고 있는 유입식변압기의 유중가스분포 특성에 대해서 설명하고 있다. 정상적으로 국내에서 운전중에 있는 변전용변압기와 발전기승압용 변압기, 산업체에서 사용되고 있는 배전용변압기의 유중가스분석결과로부터 데이터를 얻었다. 분석가스종류는 H2와 C2H2, C2H4, C2H6, CO, CO2, TCG 이며, 분포특성과 각 유중가스진단규격에서 제시하고 있는 진단기준치와의 비교 검토를 수행하였다.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.6
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• pp.136-144
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• 2004

Dissolved gas in oil analysis has been used for fault diagnosis of oil immersed insulation. In this paper to improve the reliability in deciding the degradation causes of the oil immersed insulation, we carried out electrical and thermal degradations for the insulations, and analyzed the characteristics of dissolved gases distribution on each situation. As a result more reliable faults discrimination is possible if we use the interrelation of factors like key gases and gas compositions of hydrocarbon gases and ratios of CO/$CO_2$.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.2
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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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1993.05a
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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.

• Journal of Electrical Engineering and Technology
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• v.9 no.1
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• pp.114-120
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• 2014

In this paper, a method for multi-physics analysis of the temperature-dependent properties of an oil-immersed transformer is discussed. To couple thermal fields with electromagnetic and fluid fields, an algorithm employing a user defined function (UDF) is proposed. Using electromagnetic analysis, electric power loss dependent on temperature rise is calculated; these are used as input data for multi-physics analysis in order to predict the temperature rise. A heat transfer coefficient is applied only at the outermost boundary between transformer and the atmosphere in order to reduce the analysis region. To verify the validity of the proposed method, the predicted temperature rises in high-voltage (HV) and low-voltage (LV) windings and radiators were compared with the experimental values.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.1
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• pp.53-60
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• 2010

This paper dealt with the acoustic detection of partial discharge (PD) in insulation oil for insulation diagnostics of oil immersed transformers. Electrode systems such as needle to plane, plane to plane, and floating were fabricated to simulate some defects in transformers. A wide band acoustic emission(AE) sensor with the frequency ranges of 100 kHz~1 MHz and a narrow band AE sensor with the resonant frequency of 140 kHz were used in the experiment. Also, a decoupler and an amplifier were designed to detect and amplify the acoustic signal only. The decoupler separates acoustic signal from DC source without any distortion, and the amplifier has the gain of 40 dB in frequency ranges of 11 kHz~4 MHz. In the experiment, frequency components and propagation characteristics of acoustic signal were analyzed, and an algorithm of positioning of PD occurrence by the time difference of arrival was proposed. From the results, the frequency components of the acoustic signal exist from 50 kHz to 200 kHz and the positioning error of PD calculated by three AE sensors was within 1%.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.2
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• pp.55-62
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• 2004

In this paper, the diagnostic expert system for silicone oil-filled transformer is developed using dissolved gas analysis(DGA). There are many diagnostic methods for diagnostic oil-immersed transformer. But DGA is used to the proposed expert system since it has been verified that DGA is very efficient diagnostic method for transformer. In addition, it is resonable that fuzzy rule, degree of inclusion and fuzzy measure must be considered to handle the uncertainty nature of gas boundary and rules. The proposed expert system consists of knowledge base module, inference engine module and human-machine interface(HMI) module. The knowledge base module consists of the knowledge using the rule. The inference engine module is used to the fuzzy rule. The history of the transformer gas data is managed by the database. the effect of the proposed expert system is verified by case studies.

• Proceedings of the KIEE Conference
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• 1991.07a
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• pp.292-295
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• 1991

The life of the transformers is significantly dependent upon the rate of thermal deterioration in the employed insulating materials. Therefore, the study should be based on hot-spot temperature considerations for the life expectancy and possible overload of transformer. We have measured directly temperature of the winding using thermocouples and these test results are compared with those obtained from computer simulation. In this work, our fundamental investigations are well described for the analysis in the thermal distribution of the oil-immersed transformer with the rating of 30kVA.

• Proceedings of the KIEE Conference
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• 2001.11b
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• pp.374-376
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• 2001

In this paper, we developed the fault diagnostic expert system of silicone-immersed transformer using dissolved gas analysis. The knowledge base module consists of the knowledge using the rule: if Then . The inference engine uses the fuzzy rule for the management of uncertainty of the boundary and rule and derivate the Belief and Plausibility of the normality and fault using Dempster-Shafer theory. The expert system is connected to the database and it can manages the history of gas-data of the transformer.