Electron Trapping in Polyethylene: a Molecular Modelling Study of Space Charge in the Polymeric Insulation of High Voltage Cables

The presence of space charge in the polymeric insulation of high voltage cables is correlated with electric breakdown. A direct link between molecular properties, space charge formation and eventual breakdown has still to be established. A new scheme that constitutes a first step in linking microscopic defects to the formation of space charge is suggested. The goal is to understand the role of defects at the molecular level in electron trapping and the formation of space charge in polyethylene. The analysis suggests that by defining the defect energy in terms of the molecular electron affinity, a relationship is established between the electron trap and the molecular properties of the material. Conformational defects in these waxy materials are predicted to produce shallow traps with energies below 0.3 eV, their density is estimated, and the residence time of electrons is such traps is of the order of a few picoseconds.