Evaluation of the onset of space charge and electroluminescence as a marker for cross linked polyethylene ageing

The aim of the “ARTEMIS” project is to investigate the ageing mechanisms for cross-linked polyethylene under thermo-electrical stress and to identify ageing markers, which can be used to carry out diagnostic procedures. A carefully selected set of techniques which can give cross-correlated information on space charge phenomenology and material degradation were used to investigate specimens peeled from reference and aged cables. The paper shows that ageing induces a change in the density and depth of trapping levels, and an increase in the number and size of mesovoids. Interpretation of these results is discussed in terms of physico-chemical modifications, which can affect trap distribution and microstructure

Fast soliton-like charge pulses in insulating polymers

A previously unknown mode of conduction is identified in insulating polymers at moderate fields (40-50 MV/m). This takes the form of coherent charged pulses with a mobility (similar to 10(-10) m(2)V(-1)s(-1)) several orders of magnitude larger than that traditionally associated with independent charge carriers (similar to 10(-14) m(2)V(-1)s(-1)). It is shown that this phenomenon is consistent with a mechanism in which a charged compression boundary is formed electro-mechanically during injection and thereafter travels as a coherent solitary wave (soliton) through the polymer