Jin-Woong Hong

Partial Discharge Detection of High Voltage Switchgear Using a Ultra High Frequency Sensor

Partial discharge diagnosis techniques using ultra high frequencies do not affect load movement, because there is no interruption of power. Consequently, these techniques are popular among the prevention diagnosis methods. For the first time, this measurement technique has been applied to the GIS, and has been tested by applying an extra high voltage switchboard. This particular technique makes it easy to measure in the live state, and is not affected by the noise generated by analyzing the causes of faults ? thereby making risk analysis possible. It is reported that the analysis data and the evaluation of the risk level are improved, especially for poor location, and that the measurement of Ultra high frequency (UHF) partial discharge of the real live wire in industrial switchgear is spectacular. Partial discharge diagnosis techniques by using the Ultra High Frequency sensor have been recently highlighted, and it is verified by applying them to the GIS. This has become one of the new and various power equipment techniques. Diagnosis using a UHF sensor is easy to measure, and waveform analysis is already standardized, due to numerous past case experiments. This technique is currently active in research and development, and commercialization is becoming a reality. Another aspect of this technique is that it can determine the occurrences and types of partial discharge, by the application diagnosis for live wire of ultra high voltage switchgear. Measured data by using the UHF partial discharge techniques for ultra high voltage switchgear was obtained from 200 places in Gumi, Yeosu, Taiwan and China`s semiconductor plants, and also the partial discharge signals at 15 other places were found. It was confirmed that the partial discharge signal was destroyed by improving the work of junction bolt tightening check, and the cable head reinforcement insulation at 8 places with a possibility for preventing the interruption of service. Also, it was confirmed that the UHF partial discharge measurement techniques are also a prevention diagnosis method in actual industrial sites. The measured field data and the usage of the research for risk assessment techniques of the live wire status of power equipment make a valuable database for future improvements.

Temperature dependent electrical properties in ITO/TPD/Alq3/Al organic light-emitting diodes

Temperature dependence of current-voltage-luminance characteristics in organic light-emitting diodes are studied in a device structure of ITO/TPD/Alq 3 /Al to understand an electrical conduction mechanism. The current-voltage-luminance characteristics are measured in the temperature range of 8K∼300K, and analyzed them using a hopping model with exponential trap distribution and Fowler-Nordheim tunneling. At low temperatures below 150K, the Fowler-Nordheim tunneling conduction mechanism is dominant. And we have obtained a zero field barrier height to be about 0.6∼0.8eV.

The electrical properties of silicone gel due to curing condition

In order to investigated the electrical properties of silicone gel due to the curing condition, volume resistivity and dielectric strength are investigated. Some samples made under several different curing conditions are experimented. The relationship between dielectric strength and electrode distance is investigated as well in this paper. The external 60 Hz; 3 kV/sec AC voltage is applied to the specimen until the dielectric breakdown occurs. It is proved that the electrical properties of specimen cured at 170/spl deg/C, 60 minutes and 120 minutes are superior to the others in the experimental result.

Electrical Insulation Properties of Nanocomposites with SiO 2 and MgO Filler

In this paper, we attempt to improve the electrical characteristics of epoxy resin at high temperature (above ) by adding magnesium oxide (MgO), which has high thermal conductivity. Scanning electron microscopy (SEM) of the dispersion of specimens with added MgO reveals that they are evenly dispersed without concentration. The dielectric breakdown characteristics of and MgO nanocomposites are tested by measurements at different temperatures to investigate the filler`s effect on the dielectric breakdown characteristics. The dielectric breakdown strength of specimens with added decreases slowly below (low temperature) but decreases rapidly above (high temperature). However, the gradient of the dielectric breakdown strength of specimens with added MgO is slow at both low and high temperatures. The dielectric breakdown strength of specimens with 0.4 wt% is the best among the specimens with added , and that of specimens with 3.0 wt% and 5.0 wt% MgO is the best among those with added MgO. Moreover, the dielectric strength of specimens with 3.0 wt% MgO at high temperatures is approximately 53.3% higher than that of specimens with added at , and that of specimens with 5.0 wt% of MgO is approximately 59.34% higher under the same conditions. The dielectric strength of MgO is believed to be superior to that of owing to enhanced thermal radiation because the thermal conductivity rate of MgO (approximately 42 ) is approximately 32 times higher than that of (approximately 1.3 ). We also confirmed that the allowable breakdown strength of specimens with added MgO at is within the error range when the breakdown probability of all specimens is 40%. A breakdown probability of up to 40% represents a stable dielectric strength in machinery and apparatus design.

Dielectric characteristics on insulation oil due to the aging by electron beam irradiation

The electron beam is used to change a nature of polymers in these days. When the transformer oils is irradiated with electron beam in order to investigate the dielectric characteristics, there is a morphological change. It has already confirmed that the high dose of electron beam is caused to increase the magnitude of dielectric dissipation factor, tan/spl delta/, which can be estimated to the insulation of specimen. So, in this experiment, a low dose of electron beam such as 0.5[Mrad], 1[Mrad], 2[Mrad] is irradiated. Tan/spl delta/ is measured by Video Bridge 2150 in the applying voltage range 300[mV]/spl sim/1500[mV], in the temperature range 20[/spl deg/C]/spl sim/120[/spl deg/C], and in the frequency range 30[Hz]/spl sim/1/spl times/10/sup 5/[Hz]. In addition to investigating the electrical properties of each specimen, the physical properties of each specimen is analyzed by using the FT-IR spectrum and the /sup 1/H-NMR spectrum.

Effect of the Addition of Benzotriazole on the Streaming Electrification Properties in Transformer Oil

Accidents can occur as a result of streaming electrification when transformer oil is used as an insulating oil in large ultra-high voltage transformers. Methods for adding a streaming electrification inhibitor to reduce the streaming electrification has been studied extensively. In this paper, in order to develop a method for reducing streaming electrification effectively, 4 different specimens were prepared by the addition of benzotriazole (BTA) to a virgin specimen with constant stirring. The specimens were examined to determine the appropriate amount of BTA addition that would suppress the streaming electrification most effectively. The results showed that the streaming electrification characteristics of the specimen in the streaming transformer oil were best when the amount of BTA addition was about 10 ppm. The streaming electrification current was reduced by adding 30 ppm BTA until the temperature reached 65°C. The polarity of the streaming electrification current was negative when the temperature exceeded 65°C. Therefore, the streaming electrification current, which can be a cause of transformer accidents, can be suppressed in large ultra high voltage transformer oil. This paper reports on the optimal amount of BTA addition and the best conditions for controlling the streaming velocity of transformer oil.

Conduction mechanism and stability of organic light-emitting diodes depending on the Al-based cathodes

We have studied a conduction mechanism and stability of organic light-emitting diodes with a variation of cathode materials; Al, LiAl, and LiF/Al. The organic light-emitting diodes emit a light by an injection and transport of charge carriers such as holes and electrons. Thus, the charge transport is affected by the injection barrier at the interface and hopping process in the bulk. To have an efficient organic light-emitting diodes, understanding of the electrical conduction mechanism is important. By varying the cathode materials, the electron injection at the interface could be controlled because of the work function change at the cathode. We have performed the temperature-dependent electrical properties and stability of the organic light-emitting diodes in the temperature range from 10 K to 300 K. And the devices of LiAl and LiF/AI cathode, in the lifetime and luminous efficiency, are superior to those of pure-Al.

Electrical insulating properties of nano-composites according to additive

The use of a filler material in epoxy composite materials is an essential condition for reducing the unit cost of production and reinforcing the mechanical strength. However, the dielectric strength of insulators decreases rapidly due to interactions between the epoxy resin and filler particles. In contrast to existing composite materials, nano-composite materials have superior dielectric strength, mechanical strength and enduring chemical properties due to an increase in bond strength of the polymer and nano material. It has been reported that nano-fillers provide new characteristics different from properties of the polymer material. In this study, to improve the insulation capability of epoxy resin used in the insulation of a power transformer apparatus and many devices mold. To accomplish this, the addition amount of nano-SiO2 to epoxy resin was changed and the epoxy/SiO2 nano composite materials were made, and the fundamental electrical properties of them were investigated using a physical properties and analysis breakdown test. Using allowable breakdown probability, the optimum breakdown strength for designing electrical apparatus was determined. As the result, it was found out that the electrical characteristics of the nano-SiO2 content specimens were superior to the virgin specimens. The 0.4 [wt%] specimens showed the highest electrical properties among the specimens examined with an allowable breakdown probability of 20 %, which indicates stable breakdown strength in insulating machinery design.

Dependence of the Partial Discharge Characteristics of Ultra-high Voltage Cable Insulators on the Measuring Temperature

Cross linked polyethylene (XLPE) insulators are used as insulation in ultra-high voltage electric power cables. This study investigated the electrical properties of XLPE at different temperatures. The electrical properties of the changing tree phenomenon was examined as a function of temperature applied to the electrical conductors by measuring the partial discharge at to and applied voltages to the electrodes ranging from 1 kV to 40 kV. The activity of the partial discharge was examined at various temperatures using the K-means distribution. The results revealed the specimen at to have the lowest inception voltage and breakdown voltage. In addition, the core of clusters was moved and at the positive region and and in the negative region in the K-means. The distribution of clusters was concentrated on the inception condition and spread out widely at the breakdown voltage.

Efficiency Improvement of OLEDs depending on the Hole-size of Crucible Boat

In the device structure of ITO/tris(8-hydroxyquinoline) aluminum ()/Al device, we investigated the efficiency improvement of organic light-emitting diodes (OLEDs) depending on the hole-size of crucible boat. The device was manufactured using a thermal evaporation under the base pressure of . The organics were evaporated to be 100 nm thick at a deposition rate of , and in order to investigate the optimal surface roughness of , the was thermally evaporated to be 0.8 mm, 1.0 mm, and 1.5 mm as a hole-size of the boat, respectively. We found that luminance and external quantum efficiency are superior when the hole-size of the boat is 1.0 mm. The external quantum efficiency of the device made with the hole-size of 1.0 mm boat were improved by a factor of ten compared to the devices made with the hole-size of non boat.