• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.48 no.7
• /
• pp.550-555
• /
• 1999

This paper deals with the effect of lightning impulse current on electrical characteristics of ZnO blocks used in distribution lightning arrester. The electrical characteristics of ZnO blocks are degraded by overtime impulse current, and the degraded ZnO block is brought to a thermal runaway and finally destroyed. It is therefore important to estimate the change of electrical characteristics of ZnO blocks. In this study, an impulse current generator which can produce 8/20$[\mus]$, 3[㎄] and 4/10$[\mus]$, 5[㎄] waveform is designed and fabricated to simulate the lightning impulse current of power systems. Total energy applied to the ZnO blocks at each time is 739[J] in 8/20$[\mus]$, and 523[J] in 4/10$[\mus]$, impulse current, respectively. From the experimental results, the 3rd harmonic of the leakage current increases continuously with the number of applied impulse current, but no significant changes in residual voltage and in reference voltage are observed until the ZnO block is destroyed. Also, it is confirmed that the main factor on degradation of ZnO blocks is rather the total energy applied to ZnO blocks than the peak value of the impulse current.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.5 no.3
• /
• pp.226-233
• /
• 1993

Thermosyphons are simple devices that can passively transport thermal energy over relatively large distance with little temperature degradation. Especially, the thermosyphon system requires no costly energy input and is completely maintenance free. These attributes permit the use of low grade thermal energy for thermal control of structures including the stabilization of highway foundations. This paper presents the experimental results of the snow melting system in which thermosyphon was utilized to ransfer the earth energy to the pavement to remove snow and ice. The test facility, three earth heated and one unheated test panels, is designed to investigate the variables associated with removing snow and ice from pavement surfaces. The results of these test show that the earth heated panel surface temperature is higher $2{\sim}6^{\circ}C$ than unheated panel when the ambient air temperature is $-7^{\circ}C$. The thermal performance of this earth source thermosyphon system for road heating showed that there was no snow on the heated test panels when the snowfall was 5cm average for the region.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.38 no.1
• /
• pp.79-88
• /
• 2002

13%Cr martensitic stainless steel has been used mainly with a material for fish pre-processing machinery. However, it has not very nice cutting section because of little of the carbon content. Therefore, SUS420J2 steel that contents 0.3%C with high-strength in spite of the rust is used with a material for fish pre-processing machinery. However, studies on the corrosion characteristics of SUS420J2 steel are relatively rare. Especially, the corrosion phenomenon may cause serious degradation because the fish pre-processing machinery is exposed always to seawater environment. In this paper, the immersion corrosion test was carried out at seawater environment (pH=7.52) on SUS420J2 steel specimens that have various post-treatment conditions and its corrosion characteristics were evaluated. From test results, the specimens such as base metal, vacuum heat treatment, electrolytic polishing and tempering after quenching tend somewhat sensitive from the corrosion. In the case of vacuum heat treatment specimen of continuous immersion during 360 days, the weight loss ratio was high about seven times when compared with the different specimens. On the contrary, SUS420J2 steel specimen that has the heat treatment of tempering after quenching and the electrolytic polishing was less sensitive from the corrosion, and the weight loss ratio was very low.

• Asian-Australasian Journal of Animal Sciences
• /
• v.14 no.3
• /
• pp.321-325
• /
• 2001

Two experiments were conducted to examine the degradation rates of 4 tropical legume forages in rumen and intestine of Kedah-Kelantan (KK) cattle. Three KK cattle, averaging $173{\pm}17.15kg$ each fitted with a permanent ruminal and a T-shaped duodenal cannulae were used. The cattle were fed a maintenance diet (1% DM of their body weight) composing of 60% oil palm frond (OPF) pellet and 40% of a legume mixture of Arachis pintoi (AP) and Leucaena throughout the study. The overall DM and CP degradabilities in the rumen for Gliricidia sepium (GS) and AP were significantly higher than those for Leucaena leucocephala-Bahru (LB) and Leucaena leucocephala-Rendang (LR). This implies that LB and LR would have higher dietary protein flows into the intestine for the more efficient enzymatic digestion. However, the results of the present study suggested only limited proportions of the ruminal undegraded protein in the Leucaenas were digested in the intestine.

• Transactions on Electrical and Electronic Materials
• /
• v.8 no.3
• /
• pp.115-120
• /
• 2007

Reliability between passivated and unpassivated process with the base-exposed InGaP/GaAs HBTs was studied. A passivation of HBT was attempted by $SiO_2$ thin film deposition at $300^{\circ}C$ by means of PECVD. Base-exposed InGaP/GaAs HBTs before and after passivation were investigated and compared in terms of DC and RF performance. Over a total period of 30 days, passivated HBTs show only 2% degradation of DC current gain for the high current density of $40KA/cm^2$. The measured thermal resistance of $2{\times}30{\mu}m^2$ single emitter InGaP/GaAs HBT passivated with PECVD $SiO_2$ devices can be extracted and was founded to be 1430 K/W. The estimated MTTF was $2{\times}10^7hr\;at\;T_j=125^{\circ}C$ with an activation energy $(E_a)$ of 1.37 eV.

• Nuclear Engineering and Technology
• /
• v.49 no.8
• /
• pp.1740-1747
• /
• 2017

To investigate allowable peak cladding temperature and hoop stress for maintenance of cladding integrity during interim-dry storage and subsequent transport, zirconium alloy cladding tubes were hydrogen-charged to generate 250 ppm and 500 ppm hydrogen contents, simulating spent nuclear fuel degradation. The hydrogen-charged specimens were heated to four peak temperatures of $250^{\circ}C$, $300^{\circ}C$, $350^{\circ}C$, and $400^{\circ}C$, and then cooled to room temperature at cooling rates of $0.3^{\circ}C/min$ under three tensile hoop stresses of 80 MPa, 100 MPa, and 120 MPa. The cool-down specimens showed that high peak heat-up temperature led to lower hydrogen content and that larger tensile hoop stress generated larger radial hydride fraction and consequently lower plastic elongation. Based on these out-of-pile cladding tube test results only, it may be said that peak cladding temperature should be limited to a level < $250^{\circ}C$, regardless of the cladding hoop stress, to ensure cladding integrity during interim-dry storage and subsequent transport.

• Asian-Australasian Journal of Animal Sciences
• /
• v.14 no.7
• /
• pp.941-946
• /
• 2001

The effects of various concentrations of saturated fatty acids (SFA; caprylic, capric and stearic acids) on the growth of the anaerobic fungus, Neocallimastix frontalis C5-1 isolated from the rumen of a Korean native goat were investigated. At higher concentrations of fatty acids (0.1%, w/v), the addition of SFA strongly decreased filter paper (FP) cellulose digestion and polysaccharide-degrading enzyme activity. The sensitivity of the rumen anaerobic fungus to the added fatty acids increased in the following order: caprylic ($C_{8:0}$)>capric($C_{10:0}$)>stearic($C_{18:0}$) acid, although stearic acid had no significant (p<0.05) inhibitory effects at any of the concentrations tested. However, the addition of SFA at lower concentrations (0.01 and 0.001% levels), did not inhibit FP cellulose degradation and enzyme activity. Furthermore, although these parameters were slightly stimulated by the addition of SFA, they were not statistically different from control values. This is the first report examining the effects of fatty acids on anaerobic gut fungi. We found that the lower levels of fatty acids used in this experiment were able to stimulate the growth and specific enzyme activities of rumen anaerobic fungi, whereas the higher levels of fatty acids were inhibitory with respect to fungal cellulolysis.

• Proceedings of the KIEE Conference
• /
• 1995.07c
• /
• pp.1058-1060
• /
• 1995

In this paper, we studied the tracking characteristics of silicone rubbers that differed in the degree of crosslinking. As the tracking method, we adopted ASTM D 2303 and Merry-Go-Round(MGR) test method. It was found that the higher the degree of crosslinking, the better tracking characteristics. In these two test methods, specimens showed similar tendency of performance variation according to the degree of crosslinking. However the degradation phenomena were very different. As for MGR method, only the color of specimens' surface changed without any erosion or tracking path on them. On the contrary, the specimens subjected to ASTM D 2303 test method showed severe erosion.

• Proceedings of the KSME Conference
• /
• 2001.06d
• /
• pp.903-908
• /
• 2001

A web-based client/server program, MOVIDIK(Motor-Operated-Valve Integrated Database Information of KEPCO) has been developed to perform a design basis safety evaluation for a motor-operated-valve(MOV) in the nuclear power plant. The MOVIDIK consists of seven analysis modules and one administrative module. The analysis module calculates a differential pressure on the valve disk, thrust/torque acting at a valve stem, maximum allowable stress, thermal-overload-relay selection, voltage degradation, actuator output and margin. In addition, the administrative module manages user information, approval system and code information. MOVIDIK controls a huge amount of evaluation data and piles up the safety information of safety-related MOV. The MOVIDIK will improve the efficiency of safety evaluation work and standardize the analysis process for the MOV.

• Journal of Information Display
• /
• v.12 no.1
• /
• pp.47-50
• /
• 2011

Highly stable amorphous indium.gallium.zinc-oxide (a-IGZO) thin-film transistors (TFTs) were fabricated with an etchstopper and via-hole structure. The TFTs exhibited 40 $cm^2$/V s field-effect mobility and a 0.21 V/dec gate voltage swing. Gate-bias stress induced a negligible threshold voltage shift (${\Delta}V_{th}$) at room temperature. The excellent stability is attribute to the via-hole and etch-stopper structure, in which, the source/drain metal contacts the active a-IGZO layer through two via holes (one on each side), resulting in minimized damage to the a-IGZO layer during the plasma etching of the source/drain metal. The comparison of the effects of the DC and AC stress on the performance of the TFTs at $60^{\circ}C$ showed that there was a smaller ${\Delta}V_{th}$ in the AC stress compared with the DC stress for the same effective stress time, indicating that the trappin of the carriers at the active layer-gate insulator interface was the dominant degradation mechanism.