An investigation into electrical ageing of insulating polymers by detection of charge injection under alternative divergent field

A. Hadid , C. Laurent , M. Mammeri , R. Clavreul , F. Duchateau , J. Berdala

Our aim is to understand the electrical ageing of insulating polymeric materials under a.c. voltage and in discharge-free situation, i.e. in the absence of any pre-existing gaseous cavities in the bulk of the dielectric. In this report, we use a needle electrode moulded into the insulant to simulate defects producing local field enhancement. An experimental technique for measuring the charge flow injected by the needle into the dielectric under a.c. voltage is described. The transition between the discharge-free electroluminescent state to micro-partial discharge state (early electrical tree propagation phase) is investigated with a sensitivity reaching 0.01 pC. Optical diagnosis is carried out simultaneously. Special emphasis is given to synthetic insulation of power cables. Low-density polyethylene is used as a dielectric with moulded metallic needle electrode. Semi-conducting electrodes prepared from the shield of a cable are also used in this investigation. Statistics on times to tree inception show that the needle tip cannot be considered as a homogeneous injecting surface. The conclusion is double : (i) the onset field for massive charge transfer derived from the measured curvature radius of the needle is not the absolute value and (ii) the discussion of the results obtained by a needle test must include a Weibull statistical analysis with determination of the location parameter.

Domaines: Articles anciens

A. Hadid, C. Laurent, M. Mammeri, R. Clavreul, F. Duchateau, et al.. An investigation into electrical ageing of insulating polymers by detection of charge injection under alternative divergent field. Journal de Physique III, 1994, 4 (1), pp.35-53. ⟨10.1051/jp3:1994111⟩. ⟨jpa-00249091⟩