• Journal of Electrical Engineering and Technology
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• v.10 no.1
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• pp.355-363
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• 2015

HVDC technology has become popular as an economic mode of bulk power transmission over very long distances. Polymeric insulators in HVDC power transmission lines are affected by surface tracking and erosion problems due to contamination deposit, which pose a greater challenge in maintaining the reliability of the HVDC system. In addition, polymeric insulators are also naturally affected by aging due to various environmental stresses, which in turn accelerates the surface tracking and erosion problems. Research works towards the improvement of tracking and erosion resistance of polymeric insulators by adding nano-sized fillers in the base material are being carried out worldwide. However, surface tracking and erosion performance of nano-filled aged polymeric insulators for HVDC applications are not well reported. Hence, in the present work, tracking and erosion resistance of the nano $Al(OH)_3$ filled silicone rubber insulation material has been evaluated under DC voltages at different filler concentrations and aged conditions, as per IEC 60587 test procedures. Leakage current and contact angle measurements were carried out to understand the surface hydrophobicity. Moving average technique was used to analyze the trend followed by leakage current. Water aged specimen shows less tracking resistance when compared with thermal aged specimen. It is observed that nano-filler concentration of 5% is even sufficient to get better tracking/erosion resistance under DC voltages.

• Membrane and Water Treatment
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• v.8 no.2
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• pp.113-123
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• 2017

This study investigated effects of physical and chemical cleaning methods on the initial flux recovery of fouled membrane in membrane distillation process. A laboratory scale direct contact membrane distillation (DCMD) experiment was performed to treat digested livestock wastewater with 3.89 mg/L suspended solids, 874.7 mg/L COD, 543.7 mg/L nitrogen, 15.6 mg/L total phosphorus, and pH of 8.6. A hydrophobic PVDF membrane with an average pore size of $0.22{\mu}m$ and a porosity of 75 % was installed inside a direct contact type membrane distillation module. The temperature difference between feed and permeate side was maintained at $40^{\circ}C$ with the feed and permeate stream velocity of 0.18 m/s. The results showed that the permeate flux decreased from $22.1L{\cdot}m^{-2}{\cdot}hr^{-1}$ to $19.0L{\cdot}m^{-2}{\cdot}hr^{-1}$ after 75 hours of distillation. The fouled membrane was cleaned first by physical flushing and consecutively by chemicals with NaOCl and citric acid. After the physical cleaning the flux was recovered to 92 % as compared with the initial clean water flux of the virgin membrane. Then 94 % of the flux was recovered after cleaning by 2,000 ppm NaOCl for 90 minutes and finally 97 % of flux recovered after 3 % citric acid for 90 minutes. SEM-EDS and FT-IR analysis results presented that the foulants on the membrane surface were removed effectively after each cleaning step. The contact angle measurement showed that the hydrophobicity of the membrane surface was also restored gradually after each cleaning step to reach nearly the same hydrophobicity level as the virgin membrane.

• Biotechnology and Bioprocess Engineering:BBE
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• v.6 no.4
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• pp.284-288
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• 2001

Lipid emulsions with saturated triacylglycerols (TAGs) with 4 to 10 carbons in each acyl chain were prepared to study how the oil component alters the stability of the lipid emul-sions when phosphatidylcholines were used as emulsifiers. The average droplet size of the emul-sions became smaller as the chain length of the TAG increased. For a given oil emulsion with smaller droplets was formed with an emulsifier having higher HLB value. The influence of HLB values on the droplet size was biggest for the tributyrin (C4) emulsion. For the tricaprylin(C8) emulsions, droplet size was identical at given emulsifier concentrations regardless of HLB values. The HLB value and the concentration of the emulsifiers also affect the droplet size of the emul-sions. The emulsions with smaller average droplet size were more stable than with bigger size for 20 days. The oil and water (o/w) interfacial tension in inversely proportional to the initial droplet size of the emulsion.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.565-569
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• 1999

In these days, the silicone insulators have been increasingly studied and applied for outdoor insulators because it has superior characteristics than porcelain and glass insulators, which have been used for outdoor insulators. First of all, The excellent performance of the silicone rubber in polluted and wet conditions is attributed to the ability of the material to maintain the hydrophobicity of the surface in the presence of severe contamination and wet conditions. This is because of the presence of low molecular weight mobile fluid in the silicone rubber which diffuses to the surface and to above the contamination layer. But, the leakage current and some surface discharge occurs on surface of the composite polymeric insulation materials when the insulator is used for a long time with severe contaminative condition and it can lead the contamination flashover. So the leakage current and the discharge current are important to estimate the condition of the silicone rubber surface. In this paper, the average leakage current, the relation of surface discharge current and phase angle were study to investigate electrical conduction of silicone rubber surface with the salt fog condition.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.06a
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• pp.25-28
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• 1998

In this study, we investigated the electrical characteristics of silicone rubber that being used outdoor insulating material, which had been immersed in salt water. After immersed the sample in salt water, we measured surface hydrophobicity, weight loss and microscopic surface appearance, and then compared with these of the original. And we tested the electrical characteristics of the aged sample by the water under salt-fog. These electrical characteristics are described by the average of leakage current, peak pulse number, which are recorded by data acquisition system The experimental results show that the resistance against tracking and erosion is decreased significantly by water penetration.

• Tribology and Lubricants
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• v.37 no.3
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• pp.106-111
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• 2021

There are several studies on reducing the friction that occurs on the relative sliding contact surface of moving parts under extreme environments. In particular, a solid lubricated bearing is studied to solve the tribological problem with friction reduction and durability parts using solid lubricants (lead or silver) in a vacuum atmosphere. Galinstan is mainly used as a liquid metal lubricant, but it is inevitable to have limited tribological applications owing to its high coefficient of friction. Many researchers work on surface texturing for surface modification and precision processing methods. To increase durability and low friction, DLC coating with hydrophobicity is applied on the contact surface texture. Therefore, using an untextured specimen, a dimple specimen, and a DLC-coated dimple specimen under liquid metal lubrication, this paper presents the following experimental sliding friction characteristics in the sliding friction test. 1) The average coefficient of friction of the DLC-coated dimple specimen and dimple specimen are lower compared to that of a non-patterned specimen. 2) In the DLC-coated dimple specimens, the average coefficient of friction changes according to the change in the dimple density. 3) DLC-coated dimple specimens with a density of 12.5 have the lowest average coefficient of friction under 41.6 N of normal load and 143.3 RPM.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1621-1623
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• 1999

Recently, high voltage outdoor ploymer insulators have been widely used commercially owing to their excellent electrical and mechanical properties, superior comtamination flashover performance, light weight, easy installation or handing, no maintenance during service, competitive price and so on. compared to porcelaain and glass insulators. For instance, silicone rubber(SR) for polymeric insulators specially has much superior insulating and anti-pollution performance due to its specific hydrophobicity even in severe contaminated environments. We have investigated surface discharge current characteristics of silicone rubbers(SR) for HV outdoor composite insulation specimen under accelerated aging codition using a computer measuring system. The relations of average leakage current and surface discharge current repetition rates and discharge current amplitude, the distribution of discharge current amplitude were studied to investigate electrical conduction of silicone rubber surface with the salt fog condition.

• Bulletin of the Korean Chemical Society
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• v.31 no.2
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• pp.291-297
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• 2010

This article introduces a facile nanoparticle self-assembly/annealing method for the preparation of nanoisland films. First, nanoparticle-polymer multilayer films are prepared with layer-by-layer assembly. Nanoparticle multilayer films are then annealed at $~500^{\circ}C$ in air to evaporate organic matters from the films. During the annealing process, the nanoparticles on the solid surface undergo nucleation and coalescence, resulting in the formation of nanostructured gold island arrays. By controlling the overall thickness (number of layers) of nanoparticle multilayer films, nanoisland films with various island density and different average sizes are obtained. The surface property of gold nanoisland films is further controlled by the self-assembly of alkanethiols, which results in an increased surface hydrophobicity of the films. The structure and characteristics of these nanoisland film arrays are found to be quite comparable to those of nanoisland films prepared by vacuum evaporation method. However, this self-assembly/annealing protocol is simple and requires only common laboratory supplies and equipment for the entire preparation process.

• Bulletin of the Korean Chemical Society
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• v.34 no.12
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• pp.3805-3810
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• 2013

The surface modification of silica particles (SPs) was systemically conducted by the treatment of 0.1-10 wt % phenylsilanetriol (PST) on the basis of SPs used through two step processes: 1) the PST coating of SPs via evaporation under reduced pressure and 2) their thermal condensation leading to Si-O-Si bond formation via heating at $130^{\circ}C$. The evaluation of the modified SPs was conducted by the simple floating test on water and the measurement of the contact angle (CA) of water droplet on the 2-dimensional layer of modified SPs on slide glass. When PST was used about 2 wt % or above on the basis of SPs (about average size: 50 nm) used, the modified SPs were fully floated on the water and all dispersed into upper organic solvent layer after a shaking with the mixture of the water and benzene, indicating that the modified SPs have hydrophobic properties. The modified SPs were characterized by $^{29}Si$ MAS NMR and physicochemical properties including SEM, TEM, BET, adsorption/desorption isotherms, etc. were measured and compared each other in details. This research demonstrates that the organosilanetriol is a good modifier applicable for the surface modification of inorganic oxide particles using a low amount of modifier on the basis of oxide particles used.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.509-512
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• 1999

The main problem in porcelain as a high voltage insulator is that the water film is felled on the insulator surface due to rain, flog, and dew. In the presence of contamination. leakage current increases which may lead to flashover that could be followed by an outage of the power system. These days, high voltage polymer outdoer insulators have been studied and widely used, because they have excellent electrical and mechanical properties, superior performance of flashover for contamination. light weight, easy installation or handling. no maintenance during service, competitive price, and so on. First of a1l the excellent performance of the silicone rubber in polluted and wet conditions is attributed to the ability of the material to maintain the hydrophobicity of the surface in the presence of severe contaminants and wet conditions. This is due to a low surface energy of the silicone rubber. But the leakage current and some surface discharge occurs on the surface of insulator when the insulator is used for a long time. So the leakage current and the surface discharge current are important lo estimate the condition of the silicone rubber surface. In this paper, the average leakage current the surface discharge current the surface rubber surface with the salt fog condition for the first stage.