Fumio Sawa

Effects of nano- and micro-filler mixture on electrical insulation properties of epoxy based composites

This paper focuses on the electrical insulation properties of a newly prepared composite material by nano- and micro-filler mixture. Nano- and micro-filler mixture composites were made by dispersing nano-scale layered silicate fillers and micro-scale silica fillers in epoxy resin. To investigate the effects of nano- and micro-filler mixture, the thermal expansion coefficient and insulation breakdown properties by a needle-plate electrode method were measured for the filler mixture composite and the conventional filled epoxy. The filler mixture composite had almost the same thermal expansion coefficient as the conventional filled epoxy. In a continuous voltage rising test, the filler mixture composite had 7% higher insulation breakdown strength than the conventional filled epoxy. Moreover, under constant AC voltage (10 kV at 1 kHz), the filler mixture composite had an insulation breakdown time of more than 20,000 minutes whereas the conventional filled epoxy had a breakdown time of 830 minutes. Electron microscope observation showed that the area surrounded by dispersed micro-scale silica fillers were also filled with the nano-scale layered silicate fillers. Furthermore, the estimate of spacing between the fillers and the filler/epoxy interface area showed a more densely-packed structure of the filler mixture composite than the conventional filled epoxy. The morphological feature of the filler mixture composite seems to improve its insulation breakdown strength and time.

Influence of temperature on mechanical and insulation properties of epoxy-layered silicate nanocomposite

The aim of this study is to investigate the influence of temperature on the mechanical and insulation properties of a newly developed epoxy-layered silicate nanocomposite. This nanocomposite has a higher thermal resistance with respect to mechanical properties than a base epoxy resin (epoxy resin without fillers). The volume resistivity of the nanocomposite gradually decreases with increasing temperature, and its relative permittivity gradually increases with increasing temperature. Its properties are more dependent on temperature than those of the base epoxy resin. Moreover, under a constant AC voltage, the insulation breakdown time of the nanocomposite was twice as long as that of the base epoxy resin at 20 /spl deg/C and six times as long at 80 /spl deg/C. In particular, at 145 /spl deg/C, the nanocomposite had a breakdown time of more than 20,000 minutes while the base epoxy resin had breakdown time of 280 minutes. This improvement in breakdown time resulted from electrical treeing shapes with many branches and smaller internal stress of the nanocomposite in comparison with the base epoxy resin.

Improving Epoxy-based Insulating Materials with Nano-fillers toward Practical Application

A primary concern in recent nanocomposite research is practical application. In this study, various kinds of epoxy-based nanocomposites were made and their properties evaluated to determine their applicability as insulating materials for heavy electric apparatuses. Experimental results demonstrated that nano-fillers enhance insulation breakdown properties in nanocomposites. Moreover, nano- and micro-filler combinations were adopted as an approach toward practical application of nanocomposite insulating materials. These nano- and micro- filler mixed composites had the same low thermal expansion as aluminum, and insulation breakdown properties superior to those of conventional insulating materials. Consequently, an aluminum conductor and a vacuum interrupter were molded by the nano- and micro-filler mixed composites for the first time in nanocomposite research.

Insulation properties of nano- and micro-filler mixture composite

This paper presents the electrical insulation properties of a newly-developed composite material comprising a nano- and micro-filler mixture. The filler mixture composite was made by dispersing layered silicate fillers and silica fillers in epoxy resin. The filler mixture composite had the same low thermal expansion as aluminum. Moreover, comparison with other composites demonstrated the effects of the filler mixture. The filler mixture composite showed excellent insulation breakdown properties in needle-plate electrode geometry. Microscope observation indicated a densely-packed structure of the filler mixture composite. The morphological feature seems to have an impact on the improvement of insulation breakdown properties.

Comparison of Insulation Breakdown Properties of Epoxy Nanocomposites under Homogeneous and Divergent Electric Fields

This paper focuses on the insulation properties of nanocomposites, which are evaluated under divergent and homogeneous electric fields. Epoxy nanocomposites were made by dispersing nano-fillers. Various kinds of nano-fillers were used, such as layered silicate, silica and titania. Insulation breakdown tests by needle-plate and plate-plate electrode configuration were conducted on the nanocomposites. The insulation properties of nanocomposites are superior to those of the base epoxy resin under a divergent electrical field. In particular, the nanocomposite containing TiO2 nano-fillers shows unique properties. However, there was no significant difference between the base epoxy resin and the nanocomposites under homogeneous electric fields.

Partial discharge resistant enameled wire

Accompanied with the prevalence of motors controlled by the inverter, the problem of surge voltage arising from the inverter has become intensified. The high frequency components of the inverter switching pulse voltage lead to the overvoltages due to the impedance of the cable between the inverter and the motor, and the insulating materials have been damaged by the partial discharges. In this study, we prepared an wire enamel hybridized with nano-scale inorganic particles, and investigated the properties of the enameled wire. By the uniform hybridization of a small amount of nano-scale inorganic particles to the wire enamel, the insulation breakdown time was improved by some ten times compared with that of the standard enameled wire, and it showed a good partial discharge resistance.

Preparation and insulation properties of epoxy-layered silicate nanocomposite [insulating material applications]

Herein, we report the insulation properties of an epoxy-layered silicate nanocomposite, prepared by dispersing modified layered silicates in an epoxy resin. This nanocomposite has an intercalated structure formed by the insertion of resin molecules into the spaces between each silicate layer, and it has higher insulation breakdown strength than that of an epoxy resin without layered silicate fillers. The electrical treeing progress, with many branches, in the nanocomposite seemed to result in an increase in insulation breakdown strength. These results suggest the possibility of their application as insulating materials in heavy apparatus.

Evaluation of insulation properties of epoxy resin with nano-scale silica particles

Epoxy resin containing nano-scale silica particles was prepared to evaluate partial discharge degradation and insulation breakdown strength. This material showed superior partial discharge resistance and breakdown strength to epoxy resin without silica particles. Moreover, the focus was on dimension of silica particles and a silane coupling agent to investigate the influence of epoxy/silica interface. Interface bonding by the coupling agent between the nano-scale silica particles and the epoxy resin played more important role on breakdown strength than that of micro-scale silica particles. This result was explained by simple models of nano- and micro-composites.

Properties of high-thermal conductive composite with two kinds of fillers

Thermal conductive composites made with several types of filler have been studied based on the electrical and mechanical properties. It is clarified that the thermal conductivity of the composite made with a boron nitride increases by further introducing carbon black into the matrix resin.

Roles of Fillers on Properties of Nano-TiO2 and Micro-SiO2 Filler Mixed Composites

Practical application is a primary concern in recent nanocomposite research. In an effort to use nanocomposites as insulating materials for heavy electric apparatus, titania nano-filler and silica micro-filler mixed composites were newly prepared for this study. These composites had the same low thermal expansion as aluminum and insulation breakdown properties superior to those of conventional insulating materials. Experimental results demonstrated that the titania nano-fillers enhance insulation breakdown properties and silica micro-fillers decrease thermal expansion. Moreover, these composites show synergy effects of filler mixture on insulation breakdown properties.