Recently, polymer nanocomposites (NCs) are gaining new attraction as insulating materials, since their superior dielectric properties are being recognized. In the present paper, basic dielectric properties of NCs of low-density polyethylene (LDPE) and magnesium oxide (MgO) nano-fillers with various filler contents are examined. The samples tested were LDPE/MgO NC sheets with a thickness of about 100 µm, which contain 1, 5, and 10 phr (parts per hundred parts of resin by weight) MgO particles with average and max diameters of 50 and 200 nm, respectively. As a reference, LDPE without MgO particles was also used. Instrumental analyses were carried out by ultraviolet-visible absorption spectroscopy (UVA), differential scanning calorimetry (DSC), X-ray diffraction (XRD) spectroscopy, and Fourier-transform infrared absorption (FT-IR) spectroscopy. Permittivity was measured at temperatures from 20 to 100 °C for frequencies from 30 to 10 5 Hz. Conduction current was measured under dc electric field of 25 kV/mm. Space charge distribution was measured at room temperature by the pulsed electroacoustic method. Optical transparency first increases by the addition of MgO fillers up to 1 to 5 phr, and then it decreases. Thermal properties and morphology are insensitive to the filler addition, as far as those analyzable by XRD, FT-IR, and DSC are concerned.

Polymer nanocomposite has been attracting much attention as a new insulating material, since homogeneous dispersion of only few nm-sized inorganic fillers can improve various properties significantly. In the present article, we report measurement results of permittivity, conduction current, and space charge distribution profiles observed in low-density polyethylene/MgO nanocomposites with various filler contents. The permittivity shows the lowest value at I-phr addition of fillers and then increases monotonically with an increase in the filler content. The volume resistivity measured under a dc electric field becomes highest at 5 phr in the temperature range between 278 and 363 K. There is a possibility that molecular motions, which help electronic or ionic charge carriers escape from traps by hopping, are restricted by the addition of a proper quantity of nano-fillers. In all the samples, homocharge is found to be formed before the anode. INTRODUCTION Polymer nanocomposite (NC) is an innovative polymer, in which only a small quantity of nm inorganic fillers are dispersed. It has been attracting much attention as an engineering plastic since various properties, especially mechanical and thermal properties, are improved [1]. It is desirable if such NCs can be used as electrical insulating materials [1][2][3][4]. In this research, we measured the permittivity, conduction current, and space charge profile of NCs with low-density polyethylene (LDPE) and MgO.

Abstrflct-We have constructed a model Superconducting Cylindrical (Tubular) Linear Induction Motor (SCLIM) to clarify the behaviors (AC loss, stability and so on) of A C superconducting windings in a realistic operational environment of electrical rotating machines. The studies of an A C superconductor's development in regard to the reduction of A C loss and the improvement of current capacity have been advanced. From now on, the valuation of characteristic of A C superconducting windings in a realistic operational environment should be investigated. I n the previous paper we presented the design and construction of S C L l M model system composed of AC superconducting primary windings, FRP cryostat and V V V F power supply with quench detection and protection circuit, and the results of fundamental driving experiments. I n this paper, we optimize the current distribution in primary windings to enhance the thrust characteristics and the quench detection and protection system for A C superconducting machines by a numerical approach based on the developed FEM computer program. The measurements of the thrust force, the distributions of the magnetic flux density and primary current in the S C L l M model are also shown. hftx Terms-Superconducting cylindrical linear induction motor, optimization of primary current distribution, quench detection and protection circuits, finite element analysis.I. 1NTRODUCTlON o realize AC superconducting devices, we have constructed a Linear Induction Motor with superconducting primary windings as a model device to clarify the characteristics of AC superconducting windings (e.g., stability and AC loss) in a realistic operational environment of electrical machines. The studies of an AC superconductor's development in regard to the reduction of AC loss and the improvement of current capacity have been advanced. From now on, the valuation of characteristic of AC superconducting windings in a realistic operational environment of electrical machines should be investigated. For example, T In real devices, superconducting wires are exposed to a complicated external magnetic field and the excited currents in superconducting windings are not always sinusoidal and sometimes contain harmonics. How do the above conditions influence AC loss and stability?T. Kikuma is with the