• Fire Science and Engineering
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• v.15 no.4
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• pp.78-85
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• 2001

This dissertation is research on the fireproof characteristic of molded transformer and the extinguishable characteristics of the NAF S-III. As the research method, a theoretical examination has been made for the combustion process of epoxy resin, which was the main material of molded transformer, and extinguishing process of NAF S-III, which has recently been used in the clean extinguishable chemicals. Furthermore, for its proof, the experiments on combustion and extin-guishment on molded transformer has been performed. By installing the actual molded transformer in and artificial the horizontal heating furnace which has similar conditions with the electrical substation, and after subsequently ignited, the extinguishing process has been observed by classifying it into the natural extinguishment of the ignited transformer, and extinguishable chemical in NAF S-III has been injected. The volume of injected extinguishable chemical was the economical amount which was equipped with the extinguishable capability on the molded transformer under combustion, and it was calculated with the Announcement of the Ministry of Government Administration and Home Affairs as the basis. With the injection of the calculated extinguishable chemicals, the ignited transformer has completely extinguished within one minute.

• Journal of Ceramic Processing Research
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• v.13 no.spc2
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• pp.332-335
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• 2012

A molded transformer is maintenance-free, which makes it unnecessary to replace the insulating material, like in an oil-filled transformer, because the epoxy, which is a molded insulating resin, does not suffer variations in its insulating performance for heat cycles over a long time, as compared to insulating oil. In spite of these advantages, a molded transformer may still be accessed by the user, which is not good in regards to reliability or noise compared to the oil transformers. In particular, a distrust exists regarding reliability due to the long-term insulating performance. These properties have been studied in regards to the improvement of epoxy composites and molded transformer insulation. There have nevertheless been insufficient investigations into the insulation properties of epoxy composites. In this study, it is a researching of the epoxy for insulating material. In order to prepare the specimens, a main resin, a hardener, an accelerator, and a nano/micro filler were used. Varying amounts of TiO2 and ZnO nano fillers were added to the epoxy mixture along with a fixed amount of micro silica. This paper presents the DC insulation breakdown test, thermal expansion coefficient, and thermal conductivity results for the manufactured specimens. From these results, it has been found that the insulating performance of nano/micro epoxy composites is improved as compared to plain molded transformer insulation, and that nano/micro epoxy composites contribute to the reliability and compactness of molded transformers.

• KIEE International Transactions on Electrophysics and Applications
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• v.5C no.5
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• pp.191-195
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• 2005

This paper presents an assessment method in integrity of the windings in cast resin molded transformers by using vertical analysis of thermal distribution. The proposed method is to compare the temperature distribution in a sound specimen with that in the faulted specimen with a layer to layer short circuit. Temperature distribution was acquired by an infrared thermography system, and the Arrhenius equation was adopted to the accelerated test. The proposed method can be used to detect the failures in the transformers.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.05a
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• pp.23-28
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• 2000

Insulator systems using resin casting apparatus are useful to realize the high capacity, small size, and combined electric power equipments, and are expected to bring various advantages. In Korea, epoxy resin molded apparatus have been restricted to indoor uses till now. On the other hand, in Europe, molded insulators and transformers and so forth have been practically used since the former half of 1960's. Recently, investigation on epoxy resin materials and molded apparatus for outdoor use have ben intensively carried out. Probably, this is because electric power outdoor apparatus such as distribution transformer can be given multi-functions by using outdoor epoxy resin compound This study describes the trend on the development of epoxy mold transformers, and important technologies applied for outdoor use.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.11B no.4
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• pp.180-184
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• 2001

The high operation frequency mainly reduces transformer volume in the power supply. A high frequency and high voltage pulse transformer is designed, fabricated, and tested. Switching frequency of the transformer is 100 kHz. Input and output voltages of the transformer are 250 V and 4 kV, respectively. Normal operation power of the transformer is 3 kW. Maximum volume of the transformer is 400 $cm^3$. The power density is thus 7.5 W/$cm^3$. The transformer will be installed in a metal box that has nominal operation temperature of 85 degree centigrade. The transformer and other high voltage components in the box will be molded with Silicon RTV(Room Temperature Vulcaniza) that has a very low thermal conductivity. Procedure of design and test results are discussed. Analytical as well as experimental results of varous paramters such as transformer loss, leakage inductance, distributed capacitance are also discussed. In addition, thermal analysis results from ANSYS code for three different operation conditions are discussed.

• Journal of Electrical Engineering and Technology
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• v.1 no.3
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• pp.376-380
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• 2006

Temperature distribution measured to estimate the condition of an electrical apparatus is an absolute reference for the apparatus conditions and the difference between the reference temperature and the current temperature. Because of passive thermography, without the external thermal stimulation, the difference in surface temperature between the region of interest and back ground shows that the results can apply only to the estimation or the monitoring for the condition of loose terminal and the overload pertaining to the rise in temperature. However, a thermal diffusion in the active thermography is differently generated by the structure and condition of the surface and subsurface. This paper presents a nondestructive test using this behavior and deals with the results by heat injection and cooling to the apparatus. The buried discontinuity of subsurface could be detected by these techniques.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.3
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• pp.209-214
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• 2017

Most of the present potential transformers of train vehicles are of the oil-type filled with insulating oil and are susceptible to problems such as explosion due to the increase in the internal pressure during train operation and poor reliability near the end of their life cycle. As a solution to this problem, it is necessary to develop a molded dry-type potential transformer with excellent pressure-resistance performance using insulating resin. In order to localize the product, the Korea Railroad Research Institute has been developing a molded dry-type potential transformer. As part of this research, it is necessary to analyze the vibration characteristics of the developed product and to check the transformer performance in a vibration environment. In this study, a resonance test and simulated long-term life test of the developed product were conducted according to the KS R 9144 and IEC 61373 standards, respectively, which are vibration test methods for railway vehicle parts. Their natural frequencies were analyzed by comparing the results of the numerical modal analysis and resonance test, in order to confirm their adherence to the standards. Also, the performance test after the simulated long-term life test confirmed that the operation of the developed transformer was not problematic even in a long-time vibration environment.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.10
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• pp.1688-1693
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• 2016

In this study shall investigate the influence upon the electrical property of transformer oil due to the heat among accelerated heat degradation experiment for a constant hour in the typical insulation oils of mineral base oil, silicon base oil and vegetable oil. In addition, the electric insulation performance of insulation materials in transformer shall be evaluated through the electric property analysis according to the heat degradation of epoxy insulation material, which has been used for electric facilities such as a molded transformer.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2106-2108
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• 2005

This paper describes a method of lifetime expectation for the dry-type molded transformer which is widely used in the domestic distribution system. And the result of the temperature accelerated aging test for the winding insulation and the analyzed report on the reliability are included in this study.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.105-105
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• 2010

Voltage circuit breakers are widely used in power distribution systems to interrupt fault current rapidly and to assure the reliability of the power supply. Power distribution system requires the transformer with higher capacity than ever, but this ever, but this may be the cause. of the increasing of short circuit current in contrast to conventional one when short-circuit accident is occurred. Therefore molded case circuit breaker improved in aspects of interrupting capacity of short circuit current in this system is needed. By using the proposed methods in this paper, such as new arc quenching structure of grid would contribute to minimizing the MCCB, realization of high interrupting performance and reducing the design time and development cost.