• Responsable de formations

• Sciences de l'environnement/Ingénierie de l'environnement
  
• Sciences de l'ingénieur/Matériaux
  
• Sciences de l'ingénieur/Energie électrique
  

In the design of medium and low voltage equipment such as cable accessories, generator, motor end windings or bushings, issues with electrical field enhancement occur at interfaces between insulators and conductors, resulting in accelerated material ageing. The purpose of this paper is to present a novel dielectric composite material which has the properties to mitigate this local amplification. It is a functional dielectric which resistivity decreases by several orders with electric field from 10(14) to 10(9) ohm m up to 1 kV mm(-1) while the dielectric constant decreases from 15 to 12 in the 10(-2)-10(6) Hz range. This novel material is made with graphite nanoplatelets. It may be used as a resistive or capacitive field grading material in electrical applications.

Downsizing electronic and electric equipment requires the optimization of electric field distributions in order to avoid localized dielectric breakdown (also called partial discharges). This paper presents a novel dielectric composite material aimed at grading electrical local surface stress. This functional material has a conductivity which increases by several orders with the applied electric field giving the ability to distribute the field by itself. It is prepared for the first time by dispersing graphite nanoplatelets in a polymer and may be used as a resistive or capacitive field grading material in electronic and electrical applications. Mechanisms at the origin of the nonlinear behavior are discussed.

The aim of this paper is to investigate the influence of nonlinear parameters (threshold field, low field conductivity and nonlinearity coefficient) on the performance of a cable termination equipped with a resistive field grading tube in 50 Hz and impulse voltage. The electrical field distribution over the insulator silicone housing surface was computed and analyzed using a finite element software (Flux 2D). Comparative studies between linear field grading (r = 2.9 and 16) and nonlinear resistive field grading (12 < r < 19) show that better effectiveness is achieved with a low threshold field and a high permittivity under 50 Hz and a high nonlinearity coefficient under impulse voltage.

L'invention se rapporte à un matériau de répartition de champ électrique obtenu à partir dune formulation comprenant une matrice polymérique et une charge ou un mélange de charges conférant audit matériau une résistance électrique non linéaire.

The recycling process toward the elimination of varistor wastes into new electro-active silicon composites has been investigated. We studied the dependence of the E-J characteristics on the aggregate content in the polymer matrix. Formulations with 40 vol.% metal oxide varistor aggregates in the 100-200m range exhibit reliable nonlinear behavior with a switching voltage of 280 +/- 30V/mm. The breakdown voltage of the composite decreases as both filler's diameter and filler's volume fraction increases in the 550-220V/mm and 440-280V/mm range, respectively. This paves the way for the valorization of varistors based zinc oxide (ZnO) ceramics.