• Proceedings of the KIEE Conference
• /
• 2005.07c
• /
• pp.1909-1911
• /
• 2005

The electrical and chemical characteristics in transformer insulations are changed due to thermal stress. In the chemical property, as the Kraft paper ages, the cellulose polymer chains breakdown into shorter lengths with a corresponding decrease in both tensile strength and degree of polymerization(DP). Furthermore, cellulous chains breakdown is accompanied by an increase in the content of various furanic compounds within the dielectric liquid. It is known that furanic components in transformer oil come only from the decomposition of insulating paper rather than from the oil itself. Therefore the analysis of furan products provides a complementary technique to dissolved gas analysis for monitoring transformers when we evaluate the aging of insulating paper by the total concentration of carbon monoxide and carbon dioxide dissolved in oil only. In this paper the accelerated aging process of oil--paper samples have been investigated at a temperature up to $140^{\circ}C$ for 500 hours. The oil-paper insulation samples have been measured at intervals of 100 hours. For analysis we used high performance liquid chromatography(HPLC) in accordance with IEC 61198 method.

• Journal of the Korean Institute of Intelligent Systems
• /
• v.7 no.1
• /
• pp.45-53
• /
• 1997

This paper presents hybrid expert system for diagnosis of electric power transformer faults. The expert system diagnose and detect faults in oil-filled power transformers based on dissolved gas analysis. As the preprocessing stage, fuzzy information theory is used to manage the uncertainty in transformer fault diagnosis using dissolved gas analysis. The Kohonen neural network takes the interim results by applying fuzzy informations theory as inputs, and performs the transformer fault diagnosis. The Proposed system tested gas records of power transformers from Korea Electric Power Corporation to verify the diagnosis performance of transformer faults.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.21 no.9
• /
• pp.87-94
• /
• 2007

This paper presents new criteria for DGA(Dissolved Gases Analysis) using CDF(Cumulative Distribution Function) obtained from the data from the diagnosis of transformers operated in KEPCO over a period of 16 years. Because of differences in operating environments, construction type, oil volume, and other factors, the interpretative criteria of DGA at KEPCO differs from other standards such as IEC-60599, or Rogers and Doernenburg. To suggest the most appropriate criteria, the DGA data from transformers under normal conditions as well as from developing fault transformers were collected. Using these data, this study suggests the limitative gas level of transformers under normal operating conditions and verifies the suitability of the criteria. Because the application of this new criterion to transformers at KEPCO increases the detectable ratio of incipient faults and reduces unnecessary follow-up sampling and analysis, the new criteria yields a more reliable prediction of transformer condition.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.59 no.2
• /
• pp.212-217
• /
• 2010

When paper which was applied as insulation in oil-filled transformer was aged by thermal, its electrical, mechanical and chemical characteristics were changed and deteriorated. Therefore operating temperature was more higher, damage of paper was more quicker. Insulating paper which was generally made with cellulose was degraded, polymer of long length chain was decomposed as a monomer and CO, $CO_2$ gas and/or by-product such as furfural was produced from paper at the same time. In according with detection these gas and furfural by dissolved gas analysis(DGA) and high performance liquid chromatography(HPLC), we have investigated effects of CO, $CO_2$ gas and furfural on insulation of paper. Also we have analyzed for correlation between furfural and CO, $CO_2$ gas using linear regression method that was known as useful, credible statistical analysis.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.58 no.4
• /
• pp.499-504
• /
• 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.

• Journal of Electrical Engineering and Technology
• /
• v.9 no.6
• /
• pp.2058-2064
• /
• 2014

In transformer fault diagnosis, dissolved gas analysis (DGA) is been widely employed for a long period and numerous methods have been innovated to interpret its results. Still in some cases it fails to identify the corresponding faults. Due to the limitation of training data and non-linearity, the estimation of key-gas ratio in the transformer oil becomes more complicated. This paper presents Intuitionistic Fuzzy expert System (IFS) to diagnose several faults in a transformer. This revised approach is well suitable to diagnosis the transformer faults and the corresponding action to be taken. The proposed method is applied to an independent data of different power transformers and various case studies of historic trends of transformer units. It has been proved to be a very advantageous tool for transformer diagnosis and upkeep planning. This method has been successfully used to identify the type of fault developing within a transformer even if there is conflict in the results of AI technique applied to DGA data.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.11 no.1
• /
• pp.99-105
• /
• 1997

In the paper, aging of insulating oil in pole transformer has been studied by performing accelerated thermal aging test. Dissolved gases were extracted by air bubbling method. Concentration of dissolved gases were modified by extraction ratio of each gases in insulating oil. Aging of insulating materials were proceeded by thermal degradation and oxidation reaction. Both of the reactions followed zeroch order kinetics. Formation rate equations for hydrocarbons, carbon oxides, and hydrogen were derived. It was conformed by gas analysis and UV-Visible spectrophotometric method that iron core and copper coil in pole transformer act as catalyst during the aging process.

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

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.18 no.2
• /
• pp.55-62
• /
• 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
• /
• 2006.11a
• /
• pp.141-143
• /
• 2006

Dissolved gas analysis (DGA) is widely used to detect incipient faults in oil-filled electrical equipment. KEPCO make a rule of DGA in 1985. They have been diagnosing power transformer using their DGA criteria. In this paper, we analysis the result of DGA data about transformer in the substation. We try to find out what is cause of an error in DGA diagnosis considering accuracy in extracting gases from mineral oil in transformer. The carbon-monoxide was primary reason of warning in DGA data. We specially consider that aging is a cause of generating of carbon-monoxide in power transformer.