• Proceedings of the KIEE Conference
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• 1990.11a
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• pp.170-172
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• 1990

In a large power transformer, an insulating oil is forced to circulate for cooling the heat generated by the losses within the windings and core. When oil flows and rubs against various materials, including insulating paper and steel, electrostatic charges are separated at the interface of the oil and the solid material. This paper considers the polarity and the streaming electrification of the various materials which are used in transformer. As a result of this study, it is confirmed that the leakage current on the solid material, such as paper, is charged negative. On the other hand, the solid material, such as steel, is positively charged.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.39 no.6
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• pp.568-576
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• 1990

Recently, streaming electrification in forced oil cooled power transformer has been taken up as a serious problem. In this paper, the charging tendency of various insulation oils, such as mineral oil, polybutene and silicone oil has been measured by means of an injection type charging tendency measuring apparatus under various condition. The experimental data of the dependence of the leakage current on flow velocity and temperature of oil can be explained by considering the flow state such as laminar and turbulent flow. The effect of additives on the charging tendency of mineral oil has been investigated. BTA is regarded as the most effective retardant to electrification of oil among the additives chose for this investigation.

• Proceedings of the KIEE Conference
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• 2000.07e
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• pp.48-51
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• 2000

The purpose of this study is to find the way to reduce the electrostatics by interface activation substances added in the insulating oil with concentration[ppm]. As results, The streaming current, surface tension and viscosity of the samples added nonionic and hermaphrodic substances are decreased but the conductivity is increased at higher point than the 1[ppm](c.m.c.), the other side the same phenomena of the samples added cationic and anionic substances are discovered at the 10[ppm].

• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1410-1412
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• 1998

The purpose of this study is to find the way to prevent the electrostatics from the interface of liquid and solid by adding interface active substances to the insulating oil with concentration. As results, The streaming current, surface tension, and viscosity decreased and conductivity increased at the higher point than the c.m.c. which resulted from, the adding of the interface active substances.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1603-1608
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• 2003

The Present Study reported on the experimental and numerical results of heat transfer in the acoustic fields induced by ultrasonic waves. The strong upwards flow called as acoustic streaming was visualized by a particle image velocimetry (P.I.V). in addition, the augmentation of heat transfer was experimentally investigated in the presence of acoustic streaming and was compared with the profiles of acoustic pressure calculated by the numerical analysis. Experimental and numerical studies clearly show that acoustic pressure variations are closely related to the augmentation of heat transfer.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.655-658
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• 2002

The present paper investigated the effect of ultrasonic vibrations on the melting process of a phase-change material (PCM). Furthermore, the present study considered constant heat-flux boundary conditions unlike many of the previous researches, which had adopted constant wall-temperature conditions. Therefore in the study, modified dimensionless numbers such as Stefan and Rayleigh were adopted to represent heat transfer results. The experimental results revealed that ultrasonic vibrations accompanied the effects like agitation, acoustic streaming, cavitation, and oscillating fluid motion, accelerating the melting process as much as 2.5 times, compared with the result of natural melting (i. e., the case without ultrasonic vibration). Such effects are believed to be a prime mechanism in the overall melting process when ultrasonic vibrations were applied. Subsequently, energy could be saved by applying the ultrasonic vibrations to the natural melting In addition, various time-wise dimensionless numbers provided a conclusive evidence of the important role of the ultrasonic vibrations on the melting phenomena of the PCM.

• Proceedings of the KIEE Conference
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• 1999.07e
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• pp.2146-2148
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• 1999

The purpose of this study is to find the way to reduce the electrostatics by interface activation substances added in the insulating oil with concentration[ppm]. As results. The streaming current, surface tension and viscosity of the samples added nonionic and hermaphrodic substances are decreased but the conductivity is increased at higher point than the 1[ppm] (c.m.c.), the other side the same phenomena of the samples added cationic and anionic substances are discovered at the 10[ppm].

• Proceedings of the KIEE Conference
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• 1997.07d
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• pp.1414-1416
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• 1997

The electrical breakdown characteristics of the synthetic fluids No.2 of KS class VII used for insulating and cooling the materials for the ignition coil are studied. Also, Benzotriazole(BTA) as the streaming electrification suppressant additive is added to the oil, and the change of electrical properties due to different BTA concentration is investigated. To investigate the electrical characteristics, the breakdown strength of each specimen by an experiment for AC breakdown are analyzed. The breakdown strength of specimen by adding BTA is higher than virgin specimen in low e region, but lower than that in high region because of melting BTA. It is considered that the effective content of BTA as charge suppressant additive is about 10[ppm] from the results of AC breakdown.

• Proceedings of the KIEE Conference
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• 1997.07d
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• pp.1534-1536
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• 1997

In this paper, the streaming electrification phenomena of insulating oil by metal filters and the charge elimination method were investigated. When BTA and surfactant is molten in insulating oil, BTA appear the prevention of electrification from about 5ppm and surfactant (SP-S10, SP-S30) appear the prevention of electrification from about 20ppm. BTA increase the conductivity of insulating oil but surfactant and antioxidant(DBPC) isn't affect that.

• Knowledge Management Research
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• v.19 no.2
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• pp.91-108
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• 2018

This study mainly focused on measuring the impact of comments for a particular song on the number of streamings and downloads. We modeled multiple regression equations to perform this analysis. We chose digital music market for the object of analysis because of its inherent characteristics, such as experience goods, high bandwagon effect, and so on. We carefully utilized text mining technique in accordance with the algorithm of Naïve Bayes classifier to distinguish whether a comment for a piece of music be regarded as positive or negative. In addition, we used 'size of agency' and 'existence of hit song' as moderating variables. The reason for usage of those variables is that those are assumed to affect users' decision for selecting particular song especially when downloading or streaming via music sites. We found empirical evidences that positive comments for a particular song increase the number of both downloads and streamings. However, positive comments may decrease the number of downloads when the size of agency of the artist is big. As a result, we were able to say that a positive comment for a particular song functioned as 'word-of-mouth' effect, inducing other users' behavioral response. We also found that other features of an artist such as size of the agency that the artist belongs to functioned as an external factor along with feature of the song itself.