• Journal of Electrical Engineering and Technology
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• v.11 no.6
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• pp.1735-1743
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• 2016

Insulation of valve-side windings in converter transformer withstands pulsating voltages, which will produce more serious insulation problems. In this paper, the electric breakdown experiments of oil-paper insulation specimens were executed at pulsating voltages and different temperatures. Experiment and analysis results showed that the breakdown voltage decreased with increasing temperature under pulsating voltage. The influence of temperature proves to be more significant once the temperature exceeds a limitation threshold. A fitting formula between breakdown voltage and the temperature was reported. Finally, in order to clearly understand the breakdown properties under pulsating voltage, the electric field distribution and space charge behavior under pulsating voltage at different temperature were discussed.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.8
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• pp.1416-1422
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• 2010

$SF_6$ is the most commonly used insulating gas in electrical systems. But In these days $SF_6$ mixtures and alternative gas has been studied because of global warming. so although many studies have been carried out about binary gas mixtures with $SF_6$, few studies were presented about breakdown characteristics of $SF_6/N_2$ mixtures. At present study the breakdown characteristics of $SF_6/N_2$ mixtures in Non-uniform field was performed. In this paper, The simulation value are compared with experiment values. Streamer breakdown criterion was used for predicting breakdown voltage. For accurate simulation this simulation apply utilization factor using CST(computer simulation technology) EM $studio^{tm}$ program. AC breakdown experiments in non-uniform field was performed to compare with the breakdown simulation values. The pressure range of gas mixtures was 0.4 MPa to 0.7 MPa. The rod-plane was used and mixture ratio is $SF_6$ 20% : $N_2$ 80%. The gap lengths are 10mm to 70mm. As the pressure increase, this simulation value does not correspond to the experiment value. So this simulation need surface roughness factor. As a result of applying surface roughness factor this simulation decrease a relative error (|experiment value - simulation value| /simulation value).

• Journal of the Korean Society of Tobacco Science
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• v.11 no.1
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• pp.65-69
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• 1989

This study was conducted to obtain the breeding Information for varietal difference of leaf breakdown of flue-cured tobacco at Taegu Experiment Station, Korea Ginseng & Tobacco Research Institute In 1988. The experiment was designed in randomized block with 3 replications. And data were analyzed as spilt plot design composed with varieties for main and growth stages for sub-plots. Among the 8 varieties (NC 95, SL 72, Sleight G-28, TC 518, NC82, NC 2326, NC 567 and TC 499), first half derived from NC 95, and 4 latter varieties were used for check Plants and not derived from NC 95. Plant seedlings were transplanted in 15 April. The number of breakdown leaf were investigated twice at peak growth stage, 5 June and at early harvest stage, 30 June. NC 95 and varieties derived from NC 95 had showed significantly different on the number of breakdown leaf compared to the latter 4 ones after heavy rainfall, but there were not significantly different at the two growth stages. It was suggested that NC95 and varieties derived from NC 95 had substance to induce leaf breakdown by conditional genes after water absorption to plant tissue. Among the varieties derived from NC 95 cultivar SC 72, Speight G-28 and TC 518 had appeared significantly different on the number of breakdown leaf, respectively. These results could appreciated analogically that character of leaf breakdown were governed by heteromeric genes In NC 95.

• The Korean Journal of Ecology
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• v.19 no.6
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• pp.563-573
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• 1996

Macroinvertebrate contribution to the leaf litter breakdown of Carpinus cordata was estimated at headwater streams at Mt. Jumbong (38°03'N, 128°25'E) during spring and winter spring by using two types of litter bag. Coarse-mesh bags with 10 g of leaf letter were placed in a 1st-order stream in April (the spring experiment) and December 1995 (the winter-spring experiment). Fine-mesh bags with 5 g of leaf letter were placed in a nearby 3ed-order steam. The breakdown of Carpinus in coarse-mesh bags was rapid, and, in terms of season, leaf litter processed rapidly during spring. daily mass loss rates of leaf litter (-k±1 SE) were highest for coarse-mesh bags in the spring experiment (-0.0429±0.0048), followed by coarse-mesh bags in the winter-spring (-0.0146±0.0014), fine-mesh bags in the spring (-0.0078±0.0004), fine-mesh bags in the winter-spring experiment (-0.0054±0.0005). Macroinvertebrate contribution to the litter breakdown was estimated by the difference of % leaf letter remaining between coarse -mesh bage and fine-mesh bags. Although shredders were more abundant during the winter-spring, their contribution was greater during the spring (50%) than the winter-spring (22∼33%). This result appeared to be due to the change in the chemical composition of leaf letter during processing, and to the seasonal growth patterns of major shredder taxa.

• Journal of the Korean Society of Tobacco Science
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• v.10 no.2
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• pp.93-98
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• 1988

This study was conducted to obtain basic information for varietal difference of leaf breakdown in field of flue-cured tobacco at Taegu Experiment Station, Korea Ginseng & Tobacco Research Institute in 1987. The experiment was designed in randomized block with 3 replications, data ware analysed as Split split-plot design. Main plots were varieties, sub-plots were leaf positions, 4, 5 and 6th from bottom, and each sub-plot was divided into 3 parts with distance of midrib, 7 10 and 13em from stalk. Four varieties, NC 95, NC 2326, NC 82 and BY 4 were transplanted in 15 April, and measured the weight of leaf breakdown by artificially weighted in 5 June. The results obtained are as follows : 1. Weights of leaf breakdown according to leaf position, NC 95 were lower as 358-5799 than those of other varieties as 555-597g, were not significantly different regardless of varieties. 2. Weights of leaf breakdown in relation to distance of midrib from stack, NC 95 were lower as 309-419g than those of other varieties as 472-710g. 3. Weights of leaf breakdown were significantly different according to distance of midrib from stalk, and not significantly different according to leaf position under the same distance of midrib from stalk regardless of varieties.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.11a
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• pp.329-333
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• 1996

In this Paper, the streaming electrification of transformer oils generated at the interface of transformer oils and the AC breakdown with impurity is studied. The electrification current is measured by the electrometer connected the faraday cage. And a oil velocity is maintained equally. In case of the AC breakdown test, the temperature are 30[$^{\circ}C$], 50[$^{\circ}C$], 80[$^{\circ}C$] and 90[$^{\circ}C$], repetitively. As a result of breakdown experiment, the dielectric breakdown strength is decreased in low temperature region and is increased in high temperature region according to increase of contained sodium. In case of streaming electrification experiment, the streaming current is more increased with the specimen contained sodium than the original specimen.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.03b
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• pp.37-37
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• 2010

In these days $SF_6$ mixtures and alternative gas has been studied because of global warming. so although many studies have been carried out about binary gas mixtures with $SF_6$, few studies were presented about breakdown characteristics of $SF_6/N_2$ mixtures. In this paper, breakdown experiment values and breakdown simulation value are compared. Streamer theory was used for predicting breakdown voltage. For accurate simulation, this simulation apply utilization factor using CST program. AC breakdown experiments in non-uniform field was performed to compare with the breakdown simulation values. But with gap lengths increasing, the breakdown voltage is saturated. So simulation need surface roughness factor.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1901-1903
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• 1996

In This paper, to understand statistical properties of breakdown voltage, the experiment is performed on four gaps of different electrode area, ranging from $17.44[cm^2]$ to $1809.5[cm^2]$, in $SF_6$ gas. Statictcial property of breakdown is confirmed Weibull distribution and as area of electrode is increased, breakdown voltage is decreased and converged constant value $E_0$.

• Proceedings of the KIEE Conference
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• 1995.11a
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• pp.430-432
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• 1995

In this paper, the electron beam with 1[Mrad], 2[Mrad], 4[Mrad], 8[Mrad] and 24[Mrad] is irradiated for specimen experiments on physical properties which is investigated by FTIR, and dielectric breakdown among the electrical characteristics of specimen are carried out. For the dielectric breakdown experiment, external 60 [Hz] AC voltage is applied to specimen with the rising voltage of 3[kV/cm] until dielectric breakdown occured. We made a breakdown experiment under the temperature condition of 50[$^{\circ}C$], 100[$^{\circ}C$], 150[$^{\circ}C$] in the silicone oils of dynamic viscosity of 100[cSt].

• Proceedings of the KIEE Conference
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• 1997.07d
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• pp.1478-1480
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• 1997

We investigated the breakdown characteristic of mineral oil according to applied voltage and tip radius. In this experiment, electrode system was point-plane geometry. The tip radius of needle was 5, 10, 20 and $25{\mu}m$, respectively. Applied voltage was AC and DC. We measured breakdown voltage for each tip radius with increasing electrode gap, 2mm to 10mm. Under nonuniform electric field, breakdown strength was higher when needle was negative than when needle was positive. Because it is polarity effects due to space charge. And the more sharp tip radius, whether we applied AC or DC, the higher breakdown strength. As tip radius increase, breakdown strength decreases exponentially.