Tetsushi Okamoto

Thermal Endurance, Electrical Insulating, and Mechanical Properties of Hybrid Made with Poly(dimethylsiloxane) and Tetraethoxysilane

In this paper we present the heat-resisting properties of a hybrid made from poly(dimethylsiloxane) (PDMS) and tetraethoxysilane (TEOS) through a sol–gel reaction. It is found that the hybrid with ratio TEOS/PDMS = 10 shows a weight loss of less than 3% after aging treatment at 200 °C for 480 h in air. The reason for the good thermal endurance property is that low-molecular-weight PDMS chains bond to the surfaces of silica derived from TEOS, leading to the suppression of the thermal decomposition of the chains. After the aging treatment, the mechanical properties of the elastic modulus and breaking stress are improved and elongation at breaking decreases. It is also found that the electrical insulating properties are stable upon aging treatment.

Development of potential grading layer for high voltage rotating machine

A new potential grading layer used for a high voltage rotating machine has been developed based on the percolation behavior of composite made with a resin, triiron tetra oxide (Fe/sub 3/O/sub 4/) and/or silicon carbide (SiC). The potential grading layer was designed by using a combination of high and low resistive tapes made with a binder resin, SiC and Fe/sub 3/O/sub 4/ and showed a stable and excellent partial discharge suppression capability.

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.

Percolation phenomena of field grading materials made of two kinds of filler

Electrical properties of the composites made with polybutadiene as a binder resin and SiC and/or Fe/sub 3/O/sub 4/ as filler have been studied. It has been found that the percolation threshold p/sub c/ of Fe/sub 3/O/sub 4/ of the composite made with SiC, Fe/sub 3/O/sub 4/ and resin increases with the volume fraction of SiC. It has been suggested that blobs, dead ends and loops on the percolating paths formed by SiC particles prevent the clusters of Fe/sub 3/O/sub 4/ from growing to be a percolating path. Thus, more loading of SiC leads to larger percolating threshold p/sub c/ of Fe/sub 3/O/sub 4/.

Electrical Insulating and Heat-Resistive Properties of PDMS-TEOS Hybrid with Different Molar Ratio of TEOS to PDMS

The hybrids prepared from polydimethylsiloxane (PDMS) and tetraethoxysilane (TEOS) have been well known to be rubbery hybrid materials. In this report, the authors have investigated the electrical insulating and heat resistive properties of the hybrids by changing the molar ratio of TEOS to PDMS. The electrical insulating properties are evaluated by volume resistivity and AC breakdown strength at room temperature. The resistivity is about 1013 Ω · m and AC breakdown strength is about 25 kV/mm irrespective of the molar ratio. Heat-resistive properties are evaluated by the weight loss after keeping for 480 h at 200°C in air. The weight loss becomes smaller as the TEOS content increases, and it is less than 3%. It has been clarified that the hybrids have good electrical insulating and heat-resistive properties.

Dielectric property of composites made with polyethylene, boron nitride and carbon black

The dielectric breakdown strength of the composite with a boron nitride as an insulating filler and/or a carbon black as an electrically conductive filler was measured and discussed from the view of percolation phenomena. The dielectric breakdown strength decreases with increasing the volume of carbon black. It is dominated by finite clusters of a carbon black and is not influenced by a boron nitride. The dielectric breakdown strength is described by a function of a power law of the distance from the volume fraction of carbon black to the percolation threshold with the critical exponent of /spl nu/ = 0.9. And it was found that the percolation threshold of the composite with a carbon black and a boron nitride was larger than that of the composite with a carbon black.

Dielectric breakdown of polyethylene-carbon black composites

During the last three decades extensive and worldwide research progress was made with respect to many aspects of percolation phenomena with the advance of computer technology. The physical properties of composites are well expressed as a function of a power law of the distance from the percolation threshold to a volume fraction of a filler with each critical exponent. Electrical properties at high electric fields of composites have not yet been investigated based on the percolation theory in depth. Works on numerical modeling of dielectric breakdown have been done for a random resistor-capacitor network. The aim of this paper is to discuss the dielectric breakdown of carbon black-polyethylene composites based on the percolation phenomena of the composites. The more the dielectric breakdown strength decreases as the more carbon black is loaded. It has been found for the first time that the dielectric breakdown strength of the composites is described by a function of a power law of the distance from the volume fraction of carbon black to the percolation threshold with the critical exponent of /spl nu/ = 0.9.

Technologies for high efficiency large capacity turbine generator

For large capacity turbine generators of thermal power plants, water-cooling system has widely been applied to stator windings. TOSHIBA has developed generators using hydrogen indirectly cooled windings, which are more suitable for high efficiency and easy to maintain, with capacity of 670MVA and efficiency of 99.1%. As the bars of stator windings are cooled with hydrogen gas through the insulation surrounding the bars, it is important to suppress the temperature rise. In this paper, some technologies to realize high efficiency turbine generators, such as multiple parallel circuit winding to reduce current per single bar and ventilation system optimization are described.

Non-linear electrical property of composite materials with two kinds of filler

Electrical property of the composite made with resin as a binder resin and SiC and/or Fe/sub 3/O/sub 4/ as filler has been studied. It is found that the critical volume fraction of Fe/sub 3/O/sub 4/ in the composite made with resin and Fe/sub 3/O/sub 4/ differs from that in the composite made with resin, Fe/sub 3/O/sub 4/ and SiC. The nonlinear behavior of resistivity for electric field is controlled by percolating paths formed by SiC particles. It. is also found that the appearance of the non-linear property shifts to higher electric fields by adding Fe/sub 3/O/sub 4/ as a filler to the composite made with resin and SiC particles.

Electrical properties of composite material containing microvaristor and tetrapod ZnO

In recent years, Gas Insulated Switchgear (GIS) is becoming compact which implies a relatively high electric field in the enclosure. In the result, its compactness can make metallic particles move easily. To suppress the movement of particles in the tank of GIS, the nonlinear resistive coating has been developed [1]. The coating contains the microvaristor. However, the sedimentation of microvaristor often occurs in the microvaristor filled composite. The effective way to prevent sedimentation of microvaristors was found [2]. In the method, adding the special shaped semi-conductive zinc oxide (tetrapod ZnO) is of current interest. In this paper, the role of the second particle on the conduction was discussed.