We have developed shell type 765kV transformers for generator step-up. Our research and development for shell type 765kV transformers have been continued since 1990. The shell type 765kV transformers of single phase 3MVA for step-up and 500MVA for power transmission were developed in Dec. 1992 and Oct. 1996, respectively. 204MVA 765kV transformer for generator step-up was also developed with the basis of technique and experience to the present. Total 12 phases of 204MVA 765kV transformers will be delivered at Tangjin thermal power plant by 2006. This paper describes electrical and structural features of the shell type 204MVA 765kV transformer.

Demands for the noise reduction of a transformer has been becoming an common issue because it has been used mainly at the residence area such as an apartment complex. This paper shows 2 trouble shooting examples that high noise sources were found out structural resonance of a transformer by 120Hz exciting frequency caused from magnetostrictive vibration of core. This paper presents that vibration data are very important to find noise source and how to avoid natural frequency of core and tank wall

Because of increasing demand for safety of the power transformer, the seismic qualification process in accordance with the standard of IEEE Std 693-1997 is essentially required by customer. Dynamic analysis method and static analysis method were used to qualify the seismic withstanding of the power transformer at high seismic level. Maximum stress was detected at the connection between the main structure and appendages, and maximum displacement was detected at the point of appendage's end tip. Load path and substructure system can be considered as important elements to prevent over stress and over displacement.

The demand of Gas Insulated Transformer(GIT) using $SF_6$ gas as insulating and cooling medium is being increased dramatically in the underground substation of urban area because it has the advantages of non-flammable and non-explosive, etc. This paper describes the structural features and advantages of the gas insulated transformer compare to an oil immersed transformer, and presents a brief overview of the consideration and technology which apply to $SF_6$ gas insulated transformer.

The transformer tank is pressurized by atmosphere at the time of vacuum oiling and, plastic deformation occurs at the section of stress concentration on transformer tank at this time. It is important to predict where the sections of stress are in order to prevent deformation and to add reinforcement. This paper presents prediction results where the sections of stress are occurred and whether plastic deformation occur or not, using structure analysis program(ANSYS-design program).

In this paper, a present condition with gas-in-oil diagnosis which used to condition analysis for oil insulated transformer is investigated and reason why hydrogen used to basic diagnosis for the transformer is described. This paper gives an overview of background knowledge that should to consider as moisture detecting of oil immersed paper and how could we approach to life expectancy of oil insulated transformer through detecting furfural compound.

This paper describes the application results of an ultrasonic detection system for the power transformer. The ultrasonic detection system with 6 sensors was applied to detect partial discharge in a 154kV transformer with a dangerous levels of $C_{2}H_{2},\;C_{2}H_4$ and $CH_{4}$ gases. The ultrasonic detection tests were carried out 2 times, respectively, to confirm the existence and location of the partial discharge in the transformer. As a result of internal inspection, the arc trace between the pressure ring and core due to the partial discharge was found at the estimated position based on the amplitude and arriving time of the ultrasonic signals. Therefore, it was verified that the ultrasonic detection system is effective as a preventive diagnosis method for the power transformer. Also, the reliability of the ultrasonic detection system in detecting partial discharges in the transformer was also confirmed. It is expected, therefore, that the ultrasonic detection system will have beneficial effects on applications and verifications in detecting partial discharges for the power transformer.

The carbon film was deposited by the electrolysis of methanol solution. Carbon films have been grown on silicon substrates using the method of chemical process. From investigations of the Raman spectroscopy and the FTIR spectroscopy, the carbon film deposited by the electrolysis was identified the hydrogenated carbon film with the porous structure. The carbon film deposited by elctrolysis of methanol was identified as the hydrogenated carbon film with porous structure. Deposition parameters for the growth of the carbon films were current density, methanol liquid temperature. We electrical resistance and surface morphology of carbon films formed various conditions specified by deposition parameters. It was clarified that the high electrical resistance carbon films with smooth surface morphology are grown when a distance between the electrodes is relatively wider. We found that the electrical resistance in the films independent of both current density and methanol liquid temperature. The temperature dependence of the electrical resistance in the low resistance carbon films is different from one obtained in graphite..

This paper describes electrical resistivity, dielectric strength, thermal conductivity, thermal stability and tensile strength of mica sheet impregnated with silicone rubber resin or silicone rubber resin containing alumina powder. The mica sheet impregnated with silicone rubber resin had higher electrical resistivity, dielectric strength and tensile strength than those of virgin mica sheet. Electrical resistivity of mica sheet impregnated with silicone rubber resin containing alumina increased with increasing the amount of alumina. However, dielectric strength and tensile strength of mica sheet impregnated with silicone rubber resin containing alumina decreased with increasing the amount of alumina. The mica sheet impregnated with silicone rubber resin had lower thermal conductivity than that of virgin mica sheet. However, thermal conductivity of mica sheet impregnated with silicone rubber resin conatining alumina increased with increasing the amount of alumina. In the case of thermal stability, thermal degradation of virgin mica sheet and impregnated mica sheet with silicone rubber resin did not occur up to $1100^{\circ}C$ and $400^{\circ}C$, respectively.

Recently, application area of the thyristor is extends to power conversion systems, such as HVDC, BTB, SVC and FACTS. Therefore, reliability diagnostic technique on thyristor is needed to obtain stability and maintenance of power conversion systems. To measure the characteristics of the thyristor, test equipments which based on IEC 747-6 and KS C 7023 standard are needed. In this paper, we presents the design and manufacture of the test equipments for 6.5kV/4.2kA thyristor which used in thyristor valve of HVDC conversion systems by using test standard. Voltage, current, dv/dt and turn-off time test equipments were designed and manufactured. Each systems were made separately, but unity operation can possible.

[$TiO_2$] sol and $SiO_2$ sol were prepared using sol-gel method. As $H_{2}O$/Alkoxide ratios increased, sol had cluster structure and as $H_{2}O$/Alkoxide ratios decreased, sol had linear structure. Gelation time of $TiO_2$ sol was faster than that of $SiO_2$ sol according to the time. In comparison with initial viscosity between $TiO_2$ sol and $SiO_2$ sol, $TiO_2$ sol was highest at $H_{2}O/Ti(OC_{3}H_{7})_{4}=5$, $SiO_2$ sol was almost constant according to $H_{2}O/Si(OC_{2}H_{5})_{4}$ ratios.

This paper describes development of management software for transformers based on artificial intelligent analysis technology of dissolved gases in oil. Fault interpretation using the artificial intelligent analysis is performed by the artificial neural network and a rule based on the analysis of dissolved gases. The used gases are acetylene($C_{2}H_{2}$), hydrogen($H_2$), ethylene($C_{2}H_{4}$), methane($CH_4$), ethane($C_{2}H_{6}$), carbon monoxide(CO) and carbon dioxide($CO_2$). This software is mainly composed of gases input, fault's causes, expected fault's phenomena in detail, the decision on maintenance as well as report and gas trend windows. It is indicated that this is very powerful software for the efficient management of oil-immersed transformers using data analysis of gas components.

In this paper, We studied two methods to measure optical characteristics of an electrodeless light source using the integrating sphere(diameter 1.5m). One is to use a center measurement method and the other is to use a side measurement method. As a result of analysis, a side measurement methode without auxiliary lamp is almost similar against a center measurement with auxiliary lamp to reduce a measurement of an error for luminous flux, luminous efficacy and spectral distribution etc. Therefore, Sample which cannot measured by reason of big size and heavy weight can be measured by a side measurement method.