• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.6
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• pp.1274-1279
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• 2011

The purpose of this paper is to present the manufacturing defect and damage pattern of a 3 phase 22.9/3.3kV oil immersed transformer, as well as to present an objective basis for the prevention of a similar accident and to secure data for the settlement of PL related disputes. It was found that in order to prevent the occurrence of accidents to transformers, insulating oil analysis, thermal image measurement, and corona discharge diagnosis, etc., were performed by establishing relevant regulation. The result of analysis performed on the external appearance of a transformer to which an accident occurred, the internal insulation resistance and protection system, etc., showed that most of the analysis items were judged to be acceptable. However, it was found that the insulation characteristics between the primary winding and the enclosure, those between the ground and the secondary winding, and those between the primary and secondary windings were inappropriate due to an insulating oil leak caused by damage to the pressure relief valve. From the analysis of the acidity values measured over the past 5 years, it is thought that an increase in carbon dioxide (CO2) caused an increase in the temperature inside the transformer and the increase in the ethylene gas increased the possibility of ignition. Even though 17 years have passed since the transformer was installed, it was found that the system's design, manufacture, maintenance and management have been performed well and the insulating paper was in good condition, and that there was no trace of public access or vandalism. However, in the case of transformers to which accidents have occurred, a melted area between the upper and the intermediate bobbins of the W-phase secondary winding as well as between its intermediate and lower bobbins. It can be seen that a V-pattern was formed at the carbonized area of the transformer and that the depth of the carbonization is deeper at the upper side than the lower side. In addition, it was found that physical bending and deformation occurred inside the secondary winding due to non-uniform pressure while performing transformer winding work. Therefore, since it is obvious that the accident occurred due to a manufacturing defect (winding work defect), it is thought that the manufacturer of the transformer is responsible for the accident and that it is lawful for the manufacture to investigate and prove the concrete cause of the accident according to the Product Liability Law (PLL).

• Journal of Sensor Science and Technology
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• v.10 no.6
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• pp.295-303
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• 2001

White emission thin film electroluminecent device was fabricated with ZnS for phosphor layers and BST ferroelectric thin film for insulating layers. The ZnS:Mn and $ZnS:SmF_3$ layers were used for emission of red color. Also the $ZnS:TbF_3$ and $ZnS:AgF_3$ layers were used to emission of green and blue color, respectively. And the fabrication conditions of the BST insulating layers were followings, that is, the composition ratio of target, substrate temperature, working pressure and operating gas ratio were $Ba_{0.5}Sr_{0.5}Ti_{0.3}$, $400^{\circ}C$, 30 mTorr and 9:1, respectively. The thickness of phosphor were 150 nm for each layers and the insulating layers of upper and bottom were 400 nm and 200 nm, respectively. The luminesence threshold voltage was $75\;V_{rms}$ and the maximum brightness of the thin film electroluminecent device was $3200\;cd/m^2$ at $100\;V_{rms}$.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.9
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• pp.1561-1565
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• 2007

According to thermal degradation on power transformers, it is known that electrical, mechanical and chemical characteristics for power transformer's oil-paper are changed. In the chemical property, especially, when the kraft paper is aged, the cellulose polymer chains break down into shorter lengths. It causes decrease in both tensile strength and degree of polymerization of paper insulation. Also the paper 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 furanic degradation 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. Recently, the analysis of furanic compounds by high performance liquid chromatography(HPLC) using IEC 61198 method for estimating degradation of paper insulation in power transformers has been used more conveniently for assessment of oil-paper. It is know that the main products which is produced by aging are 2-furfuryl alcohol, 2-furaldehyde(furfural), 2-furoic acid, 2-acetylfuran, 5-methyl-2-furaldehyde, and 5-hydroxymethyl-2-furaldehyde. For investigating the accelerated aging process of oil-paper samples we manufactured accelerating aging equipment and we estimated variation of insulations at $140^{\circ}C$ temp. during 500 hours. Typical transformer proportions of copper, silicon steel and iron have been added to oil-paper insulation during the aging process. The oil-paper insulation samples have been measured at intervals of 100 hours. Finally we have analyzed that 2-furoic acid and 2-acetylfuran products of furanic compounds were detected by HPLC, and their concentrations were increased with accelerated aging time.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.1 no.2
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• pp.74-81
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• 1987

The reduction in dielectric strength of insulating polymer material when applying electric field is known to be substantial due to the trapped carrier effect. In this study, the carrier property of Biaxially-Drawn polypropylene, which has superior heat-resistance compared to ordinary one, is examined to improve electrical characteristics by measuring TSC spectra as a function of electric field applied to a sample of ($50{\mu}m$) thickness film. The TSC spectra in the temperature range of 303-413(K) and electric field of 2-80(MV/m) have shown no observable effect below 12(MV 1m) but TSC currents of Hetero-and Homo-peaks formed from trapped space charger and space charger injected from electrode have been observed above that point, which seems eventually lead to dielectric breakdown. Finally, this study has shown the superior dielectric proporty of Biaxially-Drawn polypropylene film compared to the non-oriented one for electrical insulation.

• Journal of Powder Materials
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• v.13 no.4 s.57
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• pp.256-262
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• 2006

The amorphous $Fe_{73}Si_{16}B_7Nb_3Cu_1$ alloy strip was pulverized to get a flake-shaped powder after annealing at $425^{\circ}C$ for 90 min and subsequently ground to obtain finer flake-shaped powder by using a ball mill. The powder was mixed with polyimide-based binder of $0.5{\sim}3wt%$, and then the mixture was cold compacted to make a toroidal powder core. After crystallization treatment for 1 hour at $380{\sim}600^{\circ}C$, the powder was transformed from amorphous to nanocrystalline with the grain size of $10{\sim}15nm$. Soft magnetic characteristics of the powder core was optimized at $550{\sim}600^{\circ}C$ with the insulating binder of 3wt%. As a result, the powder core showed the outstanding magnetic properties in terms of core loss and permeability, which were originated from the optimization of the grain size and distribution of the insulating binder.

• Journal of the Semiconductor & Display Technology
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• v.5 no.1 s.14
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• pp.39-43
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• 2006

The polyvinyl series organic films as gate insulators of thin film transistor(TFT) have been processed and characterized on the polyether sulphone (PES) substrates . The poly-4-vinyl phenol(PVP) and polyvinyl toluene (PVT) were used as solutes and propylene glycol monomethyl ether acetate(PGMEA) as a solvent in the formation of organic insulators. The cross-linking of organic insulators was also attempted by adding the thermosetting material, poly (melamine-co-formaldehyde) as a hardener in the compound. The electrical characteristics measured in the metal-insulator-metal (MIM) structures showed that insulating properties of PVP layers were generally superior to those of PVT layers. Among the layers of PVP series; copolymer PVP(10 wt%), 5wt% cross-linked PVP(10 wt%), copolymer PVP(20 wt%), 5 wt% cross-linked PVP(20 wt%) and 10 wt% cross-linked PVP(20 wt%), the 10 wt% cross-linked PVP(20 wt%) layer showed the lowest leakage current of 1.2 pA at ${\pm}10V$. The ms value of surface roughness and the capcitance per unit area are 2.41 and $1.76nF/cm^2$ in the case of 10 wt% cross-linked PVP(20 wt%) layer, respectively.

• Journal of the Korean Vacuum Society
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• v.6 no.3
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• pp.249-254
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• 1997

We investigated characteristics of Fe-doped semi-insulating InP by means of photoreflectance(PR) measurement. The band gap energy($E_0$) and broadening parameter($\Gamma$) from PR signals at 300K are 1.336 eV and 11.2 meV, respectively. As the temperature is decreased from 300 to 80 K, PR signals are varied from an overlapped shape of exciton and 2-dimensional band gap transitions(300 K) to that of exciton transition(80 K). We calculated Varshni coefficient($\alpha=0.94\pm$0.07 meV/K, $\beta=587\pm$35.2 K) and Bose-Einstein coefficient ($a_B=33.6{\pm}2.02meV$ , $\theta=165\pm$33K). After annealing of isothermal and isochronism crystallinity of InP is found to be excellent when annealed at $300^{\circ}C$ for 10~20 min, qualitatively.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.1202-1203
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• 2015

This paper describes the development of HVDC ${\pm}500kV$ polypropylene laminated paper (PPLP) mass-impregnated (MI) type cable system for HVDC transmission lines. As you know, mass-impregnated type cable generally has only insulating layer with the Kraft paper impregnated with a high-viscosity insulating compound. But polypropylene laminated paper is made of a layer of extruded polypropylene (PP) film sandwiched between two layers of Kraft paper. Thanks to PP film and its combination with Kraft paper, PPLP has higher AC, Impulse (Imp.) and DC breakdown (BD) strengths as well as lower dielectric loss than conventional Kraft paper insulation. In addition, Kraft MI cable has a limitation for the maximum conductor temperature as $55^{\circ}C$ But this PPLP MI cable has higher maximum conductor temperature than that of Kraft MI cable due to advantage of oil drainage characteristics. It is the most economic type of cable for HVDC transmission. Also HVDC ${\pm}500kV$ PPLP MI cable system was developed including land joints and outdoor-terminations. In order to prove the mechanical and electrical performances, the type test was carried out according to CIGRE recommendations. A full scale cable system has been tested successfully. And additional load cycle and polarity reversal tests on the cable system showed a higher performance compared with a similar mass impregnated paper cable.

• Journal of Sensor Science and Technology
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• v.9 no.1
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• pp.83-89
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• 2000

BST thin films were deposited on the ITO coated glass for using TFELD insulating layer by rf magnetron sputtering method. $O_2/(Ar+O_2)$ mixing ratio was 10%, substrate temperature was changed from R.T. to $500^{\circ}C$, and working pressure was changed from 5 mTorr to 30 mTorr. BST thin films deposited with various conditions were investigated electrical, optical, structural properties, and stoichiometry. The result of investigation was achieved good fabrication condition that substrate temperature of $400^{\circ}C$, and working pressure of 30 mTorr. Relative dielectric constant of 254 at 1 kHz, leakage current density was below $3.3{\times}10^{-7\;}A/cm^2$ at 5\;MV/cm applied electric field, and transmittance was over 82% at visible range.

• Journal of the Korean Ceramic Society
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• v.32 no.7
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• pp.761-768
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• 1995

Double layered BaTiO3 thin films with high dielectric constant as well as good insulating property were prepared for the application to low voltage driving thin film electroluminescent (TFEL) device. BaTiO3 thin films were formed by rf-magnetron sputtering technique. Amorphous and polycrystalline BaTiO3 thin films were deposited at the substrate temperatures of room temperature and 55$0^{\circ}C$, respectively. Two kinds of films prepared under these conditions showed high resistivity and high dielectric constant. The figure of merit (=$\varepsilon$r$\times$Eb.d) of polycrystalline BaTiO3 thin film was very high (8.43$\mu$C/$\textrm{cm}^2$). The polycrystalline BaTiO3 showed a substantial amount of leakage current (I), under the high electric field above 0.5 MV/cm. The double layered BaTiO3 thin film, i.e., amorphous BaTiO3 layer coated polycrystalline BaTiO3 thin film, was prepared by the new stacking method and showed very good dielectric and insulating properties. It showed a high dielectric constant fo 95 and leakage current density of 25 nA/$\textrm{cm}^2$ (0.3MV/cm) with the figure of merit of 20$\mu$C/$\textrm{cm}^2$. The leakage current density in the double layered BaTiO3 was much smaller than that in polycrystalline BaTiO3 under the high electric field. The saturated brightness of the devices using double layered BaTiO3 was about 220cd/$m^2$. Threshold voltage of TFEL devices fabricated on double layered BaTiO3 decreased by 50V compared to the EL devices fabricated on amorphous BaTiO3.