• The Transactions of the Korean Institute of Electrical Engineers A
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• v.51 no.11
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• pp.559-567
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• 2002

This paper presents the general recommendations for the overload criterions of mineral-oil-immersed distribution transformers rated 100kVA and less. For this purpose, we analyze the characteristics of top-oil temperature rising for mineral-oil-immersed power distribution transformer rated 100kVA and less, manufactured in Korea, In order to analyze the characteristics of top-oil temperature rising due to the distribution transformer loading, we performed experiments at KERI (Korea Electrical Research Institute) from December 2000 to May 2001. The restraint of ambient temperatures for the experiment results is solved using the results of foreign standards. Finally, we present the overload criterions of distribution transformer for summer and winter season, respectively.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.12
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• pp.1745-1750
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• 2017

Starting from the distribution transformer, the insulation oil for the oil immersed power transformer is being used to convert the vegetable oil from the existing mineral oil. Vegetable oil is better in temperature characteristics and insulation performance, is not toxic, and has better biodegradable characteristic than that of mineral oil. In order to investigate the corona inception voltage and dieclectic charateristics of the two insulating oils, three oil immersed transformers using mineral oil and vegetable oil were made and thermal cyclic aged. In this paper, the changes in the corona discharge inception voltage, chemical and electrical properties of the two sampled insulating oils from the transformers had been studied.

• Proceedings of the KIEE Conference
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• 2001.11b
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• pp.6-8
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• 2001

This paper covers general recommendations for top-oil temperature rising of mineral-oil-immersed power distribution transformer rated 100kVA and less, manufactured in Korea. In order to analyze the top-oil temperature rising due to the distribution transformer loading we performed experiments for oil-immersed distribution transformer, manufactured in domestic at KERI(Korea Electrical Research Institute) from December 2000 to May 2001. The magnitude of loading were changed, and the top-oil temperatures for each time were measured. Finally, we present the overload criteria of distribution transformer for summer and winter season in domestic. respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11a
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• pp.605-608
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• 2001

With the intention of investigating the breakdown properties of oil-immersed transformer oils in temperature range of 20∼100[$^{\circ}C$], we are made researches AC breakdown in the gap of 500∼2,500[$\mu\textrm{m}$]. The classification for the physical properties of oil for oil-immersed transformer by FTH and $^1$H-NMR experiments was confirmed to type of mineral oils. As the dependance of breakdown properties due to electrode gap length variation, breakdown voltage was found increasing according to the increase of gap, while dielectric strength was decreasing. As a result the characteristics for AC breakdown, It goes to prove that the breakdown voltage was increased to 90[$^{\circ}C$] but decreased over 90[$^{\circ}C$] in the temperature range. Also, breakdown voltage was found increasing in the increase of gap and the rising of temperature according to Weibull distribution.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11b
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• pp.605-608
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• 2001

With the intention of investigating the breakdown properties of oil-immersed transformer oils in temperature range of $20\sim100[^{\circ}C]$, we are made researches AC breakdown in the gap of $500\sim2500[{\mu}m]$. The classification for the physical properties of oil for oil-immersed transformer by FTIR and H-NMR experiments was confirmed to type of mineral oils. As the dependance of breakdown properties due to electrode gap length variation, breakdown voltage was found increasing according to the increase of gap, while dielectric strength was decreasing. As a result the characteristics for AC breakdown, It goes to prove that the breakdown voltage was increased to $90[^{\circ}C]$ but decreased over $90[^{\circ}C]$ in the temperature range. Also, breakdown voltage was found increasing in the increase of gap and the rising of temperature according to Weibull distribution.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05c
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• pp.203-207
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• 2002

In order to evaluate the aging of mineral oil immersed distribution transformers, it gathered some insulation oil in over loaded and long time(exceed their service life, 13yrs.) aged transformers in the field, we measured moisture content, acid number, dielectric strength of the oil as defined in KS C 2101 standard. And also, it had been measured dielectric constant, specific resistant, $tan{\delta}$ on aged transformer oil at from $10^{\circ}C$ to $130^{\circ}C$. These results are compared with a new mineral oil. From this study, it can be considered that the analysis of mineral oil may be suitable for evaluation of life expectancy in distribution transformers

• Proceedings of the KIEE Conference
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• 2004.11d
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• pp.97-99
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• 2004

Liquid-immersed pole transformers have utilized an insulation system consisting of natural cellulose-based materials and mineral oil for many years. If the transformers are installed with the abruptly changing load over limitation, its insulation materials are apt to unexpected aging with high temperature. Therefore we have been conscious of developing a transformer that is more thermally stable then conventional types. To measure temperature distribution in the winding of conventional and newly designed transformers, temperature sensors were installed fordirect reading of oil and conductor temperatures at transformers. And we conducted accelerating aging test for these transformers. The measuring data had made use of the design to hybrid insulation system. Also we could find the possibility of this insulation system to apply in pole mounted transformers.

• Proceedings of the KIEE Conference
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• 2002.07c
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• pp.1896-1898
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• 2002

In this paper, to developing thermally and mechanically upgraded ones, we dismounted pole transformers used in the fields for over 13 years and conducted aged oil analysis. Also, when the cellulose and aramid papers in test cell were aging with oil at $130^{\circ}C$ for 3000 hours, with the testing period cellulose paper deteriorated more rapidly than the others. For example dielectric strength and dissipation factor of papers deteriorated with aging time. For evaluation of thermal aging characteristics, a mineral oil-immersed transformer was constructed with hybrid insulation system comprised of aramid paper and cellulose insulation. A Hybrid system has economic advantages. Cellulose materials are confined to cooler regions of the transformer winding. And aramid papers are served to insulate contact parts of hot conductors.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1558-1560
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• 2004

Liquid-immersed pole transformers have utilized an insulation system consisting of natural cellulose-based materials and mineral oil for many years. If the transformers are installed with the abruptly changing load over limitation, its insulation materials are apt to unexpected aging with high temperature. Therefore we have been conscious of developing a transformer that is more thermally stable then conventional types. To measure temperature distribution in the winding of conventional and newly designed transformers, temperature sensors were installed fordirect reading of oil and conductor temperatures at transformers. And we conducted accelerating aging test for these transformers. The measuring data had made use of the design to hybrid insulation system. Also we could find the possibility of this insulation system to apply in pole mounted transformers.