Nanostructured materials are attracting increased interest and applications. Exciting perspectives may be offered by electrical insulation. Polymeric nanofilled materials may find new and/or upgraded applications in the electrical and electronic industry, replacing conventional insulation to provide improved performances in electrical apparatus, as regards, e.g., reliability, environmental compatibility and power rating. This paper shows that electrical properties of nanocomposite insulating materials for DC applications, specifically space charge, conductivity and breakdown voltage, can improve significantly with respect to the basis, unfilled materials. Reference is made to two polymeric materials, i.e. poly(ethylene-covinylacetate) (EVA) and polypropylene (PP), that are widely used as electrical insulation, e.g. for cables and capacitors. The nanofiller consists of an organophilic layered silicate, specifically an extra-pure synthetic fluorohectorite modified by means of interlayer exchange of sodium cations for protonated octadecylamine NH/sub 3//sup +/ (ODA), in a weight concentration of maximum 6%. In both materials the space charge accumulation rate as a function of applied electric field is significantly reduced, while the electrical conductivity is raised. The breakdown voltage can increase for the nanofilled materials.

Modification of electrical properties and performance of EVA and PP insulation through nanostructure by organophilic silicates

Polypropylene (PP) has special advantages in replacing conventional crosslinked polyethylene (XLPE) to be insulation material of power cable. In order to reveal the effects of nano-filler addition on PP, five kinds of experiments, namely TEM, DSC, breakdown strengths (BDs), space charge and dielectric measurement were investigated to evaluate the insulating properties of PP and its nanocomposites with surface-treated nano-MgO of different concentration. It is revealed that, with the addition of nano-MgO, favorable dispersibility of nano-filler and significant increase of crystallinity of polymer are observed. BDs under dc voltage increase apparently with loading of nano MgO, but when the nano concentration reaches higher than 1 wt%, the BDs have a slight decline compared with 1 wt%. It is clarified that space charge and electric field distortion are well restricted with the addition of nano-MgO, while this effect is not obvious with the nano concentration reaches 6 wt%. Permittivity has trends of increase with the rise of temperature at first and then decrease when the temperature reaches about 333 K, and the addition of nano-filler MgO could also decrease permittivity. When the nano-filler concentration reaches high, dielectric loss increases to a high level. Low nano-filler concentration in MgO/PP shows better electrical insulation properties compared with PP and high nano-filler concentration composites.

Insulating property of polypropylene nanocomposites filled with nano-MgO of different concentration

A consistent laboratory reproduction of waveforms during impulse tests with solid insulation materials has been a difficult task. Carbon polyethylene composites can serve as benchmarks for such studies. Experimental results on films and a practical voltage transformer (VT) are shown that can help develop signal analysis tools.

Carbon-polyethelene composites as bench marks for breakdown studies in windings

It has been requited to replace a thermosetting polymer used for the separator in a proton exchange membrane fuel cell (PEMFC) with a thermoplastic elastomer from the point of view of cost and size down. The separator used in the PEMFC is requited to have low resistivity, low hydrogen permeability and resistance to acid liquids. This paper addresses resistivity, results obtained by the Hall measurement, mechanical strength and hydrogen permeability of the composites made with a thermoplastic elastomer and graphite. It was found that the composites made with the thermoplastic elastomer and a graphite show a resistivity less than 20 m/spl Omega/ and low hydrogen permeability, which means that the composite is one of a promising candidate for the separator of PEMFC.

Electrically conductive composites made with TPE and graphite

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.

A. Ohshita

Papers

Dielectric breakdown of polyethylene-carbon black composites