Thermally Stimulated Discharge of Polyethylene Following Ac Stressing

Electron injection into polymers from field stress concentration sites is now generally accepted as important for the initiation of electrical trees, although very few published studieshave so far provided direct evidence for this. By means of the thermally stimulated discharge (TSD) technique in low density polyethylene (LDPE) double needle samples, electronic space charge densities of 2.7×10-3 Ccm-3 have been shown to exist in shallow (~3 μm) regions surrounding the needle tips following ac stressing at a maximum field of 1.2×108 Vm-1. The present TSD results agree well with "conventional" TSD data (planar samples, dc polarization) in the literature.