• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.11
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• pp.1571-1577
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• 2013

Electrical tree structure is one of the most important influencing factors for electrical treeing characteristics in polymers. In this paper, we focused on the structure characteristics of electrical treeing in epoxy resins (original) insulation under different high-frequency voltages (60, 500, 1000Hz). Effects of voltage frequency on the ac electrical treeing phenomena in an epoxy resins were carried out in needle-plate electrode arrangement. To measure the treeing initiation and propagation, and the breakdown rate, constant AC of 10 kV with three different voltage frequencies (60, 500 and 1,000 Hz) was applied to the specimen in needle-plate electrode specimen at $30^{\circ}C$ of insulating oil bath. At 60 Hz, the treeing initiation time was 360 min and the propagation rate was $6.85{\times}10^{-4}mm/min$, and the morphology was dense branch type. As the voltage frequency increased, the treeing initiation time decreased and the propagation rate increased. At 1,000 Hz, the treeing initiation time was 0 min and the propagation rate was $7.81{\times}10^{-2}mm/min$, and the morphology was dense bush type.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.470-474
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• 2001

IGBT inverters have switching rise times of 0.2-2 $\mu$ sec, and have been believed to cause insulation stresses and premature motor failures. Inverter driven induction motors with high speed switching and advanced PWM techniques are widely used for variable speed applications. Recently, the insulation failures of stator winding have attracted many concerns due to high dv/dt of IGBT PWM inverter output. In this paper, the detailed insulation test results of 19 low-voltage induction motors are presented. Different types of insulation techniques are applied to 19 motors. The insulation characteristics are analyzed with partial discharge, discharge inception voltage, and dissipation factor tests. Also, breakdown tests by high voltage pulses are performed, and the corresponding breakdown voltages are obtained.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.9
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• pp.1644-1651
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• 2010

VLF $tan{\delta}$ diagnosis technology is introduced in IEEE Std 400 and proposed as evaluation criterion in an effective way of detecting water tree which mainly causes the failure of XLPE insulated cables. In order to inspect the accuracy of the VLF $tan{\delta}$ method for XLPE insulated power cables in Korean distribution system, diagnosis for 41 cables which were being serviced in the fields has been carried out and they were removed for AC breakdown voltage test after. Regarding the 41 cables, it was hard to confirm any relation between the VLF $tan{\delta}$ values and AC breakdown voltages and also water tree in the insulation was not detected. However, the other cables were failed several days after the diagnosis of the 41 cables. Water trees were found and their VLF $tan{\delta}$ values were also much higher than the criterion of IEEE standard. It has been ascertained that we need to change the IEEE criteria in order to improve the accuracy of detecting water trees by additional analyzing of field examples of failure and case studies from overseas countries and therefore amended VLF $tan{\delta}$ test voltage and evaluation criteria have been proposed.

• Journal of Electrical Engineering and Technology
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• v.8 no.5
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• pp.1157-1162
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• 2013

We proposed AlGaN/GaN high-electron-mobility transistors (HEMTs) using thermal oxidation for NiOx passivation. Auger electron spectroscopy, secondary ion mass spectroscopy, and pulsed I-V were used to study oxidation features. The oxidation process diffused Ni and O into the AlGaN barrier and formed NiOx on the surface. The breakdown voltage of the proposed device was 1520 V while that of the conventional device was 300 V. The gate leakage current of the proposed device was 3.5 ${\mu}A/mm$ and that of the conventional device was 1116.7 ${\mu}A/mm$. The conventional device exhibited similar current in the gate-and-drain-pulsed I-V and its drain-pulsed counterpart. The gate-and-drain-pulsed current of the proposed device was about 56 % of the drain-pulsed current. This indicated that the oxidation process may form deep states having a low emission current, which then suppresses the leakage current. Our results suggest that the proposed process is suitable for achieving high breakdown voltages in the GaN-based devices.

• Journal of the Korean Vacuum Society
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• v.11 no.4
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• pp.212-217
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• 2002

A new technique for highly controllable trench corner rounding at the top and bottom of the trench using pull-back and hydrogen annealing has been developed and investigated. The pull-back process could control the trench corner rounding radius at the top comers of the trench. The silicon migration generated by hydrogen annealing at the trench coiners provided (111) and (311) crystal planes and gave a uniform gate-oxide thickness, resulting in high reliable trench DMOSFETs with highly breakdown voltages and low leakage currents. The breakdown voltage of a trench DMOSFET fabricated using hydrogen annealing was increased by 25% compared with a conventional DMOSFET. The reasonable drain current of 45.3 A was obtained when a gate voltage of 10 V was supplied. The on-resistance of the trench gate DMOSFET fabricated using the trench cell of 45,000 was about 55 m(at a gate voltage of 10 V under a drain current of 5 A.

• Journal of Electrical Engineering and Technology
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• v.11 no.3
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• pp.690-698
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• 2016

In this paper, a study is carried out to investigate the dielectric, physical and chemical properties of Palm Oil (PO) and Coconut Oil (CO) under open thermal ageing condition. The type of PO used in this study is Refined Bleached and Deodorized Palm Oil (RBDPO) Olein. The ageing experiment was carried out at 85 ℃ and 115 ℃ for 1, 3, 5, 7 and 14 days. Several parameters were measured such as AC breakdown voltage, dielectric dissipation factor, relative permittivity, resistivity, viscosity, moisture and acidity throughout the ageing duration. Based on the study, it is found that there are no significant changes on the AC breakdown voltages and relative permittivities for both RBDPO and CO. At ageing temperature of 115℃, there are clear reduction trends of dielectric dissipation factor for CO and resistivities for most of RBDPO. On the other hand, no clear trends are observed for viscosities, moisture and acidities of RBDPO and CO throughout the ageing duration.

• Applied Science and Convergence Technology
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• v.25 no.1
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• pp.15-18
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• 2016

Study investigated the optimal anodizing conditions for fabricating an oxide film that produces less contamination in a corrosive plasma environment, using oxalic acid and tartaric acid. Oxide films were produced using sulfuric acid, oxalic acid, and tartaric acid electrolyte mixtures with various mole ratios. The oxide film made by adding 0.05M tartaric acid to 0.3M oxalic acid showed higher breakdown voltage and lower leakage current. Additionally, contamination particles were reduced during plasma etching, thus demonstrates that this mixture presented optimal conditions. However, higher tartaric acid content (0.1 M, 0.15 M) led to lower breakdown voltages and higher leakage currents. Also, it resulted in more cracking during thermal shock tests as well as the generation of more contamination particles during plasma processing.

• Korean Journal of Materials Research
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• v.1 no.3
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• pp.132-138
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• 1991

A comparision was made on the influence of BPSG flow temperatures on the electrical properties in submicron CMOS DRAMs containing two BPSG layers. Three different combinations of BPSG flow temperature such as $850^{\circ}C/850^{\circ}C,\;850^{\circ}C/900^{\circ}C,\;and\;900^{\circ}C/900^{\circ}C$ were employed and analyzed in terms of threshold, breakdown and isolation voltage along with sheet resistance and contact resistance. In case of $900^{\circ}C/900^{\circ}C$ flow, the threshold voltage of NMOS was decreased rapidly in channel length less than $0.8\mu\textrm{m}$ with no noticeable change in PMOS and a drastic decrease in breakdown voltages of NMOS and PMOS was observed in channel length less than and equal to $0.7\mu\textrm{m}$ and $0.8\mu\textrm{m}$, respectively. Little changes in threshold and breakdown voltages of NMOS and PMOS, however, were shown down to channel length of $0.6\mu\textrm{m}$ in case of $850^{\circ}C/850^{\circ}C$ flow. The isolation voltage was increased with decreasing BPSG flow temperature. A significant increase in the sheet resistance and contact resistance was noticeable with decreasing BPSG flow temperature from $900^{\circ}C$ to $850^{\circ}C$. All these observations were rationalized in terms of dopant diffusion and activation upon BPSG flow temperature. Some suggestions for improving contact resistance were made.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.16 no.1
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• pp.27-34
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• 2002

In this paper, characteristics of the ac and dc flashover voltage in the horizontal air gap of a needle-needle electrode system were investigated when the combustion flame was present near the high-voltage electrode. In order to examine the flashover phenomena and the corona inception voltages caused by flame we measured the voltage and current waveforms when the corona and the flashover was occurred. We also observed, as increasing the applied voltages, the deflection or fluctuation phenomena in the shape of flames caused by the corona wind and the coulomb's force. As the results of an experimental investigation, we found that the reduction of flashover voltages, in comparison with the no-flame case, are 62.7[%] for k=1.0, 34.2[%] for h=5[cm], 27.3[%] for h=7[cm] and 21.4[%] for h=9[cm] when ac voltage is applied.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.5
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• pp.257-262
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• 2006

To evaluate the change in protective levels of zinc oxide (ZnO) varistors after the surge absorption, this paper investigated the effects of the number of injection and amplitude of lightning surges on the life of ZnO varistors for low voltages. Leakage currents flowing through ZnO varistors subjected to the $8/20{\mu}s$ impulse currents under 60 Hz AC voltages were measured. The surge simulator system ECAT that can generate $8/20{\mu}s$ impulse currents with a peak short-circuit of 5 $[kA_p]$ was used. The ZnO varistor leakage current increases with exposure to impulse current, and the number of injection of $8/20{\mu}s$ impulse currents to breakdown was inversely proportional to the amplitude of the test current. Behaviors of ZnO varistor leakage currents were strongly dependent on the number of injection and amplitude of $8/20{\mu}s$ impulse currents. ZnO varistors degrade gradually when subjected to impulse current, and the resistive leakage current flowing through ZnO varistors subjected to the $8/20{\mu}s$ impulse currents under 60 Hz AC voltages was significantly increased after a certain number of injection that is dependent on the amplitude of the test impulse current. As a result, the life of ZnO varistors mainly depends on the amplitude and occurrence frequency of lightning surges.