Anomalous currents in highly insulating materials

Transient anomalous discharging currents (ADC) in low-density polyethylene (LDPE) have been reported (anomalous currents being currents which flow in a direction opposite to that expected). Transient anomalous charging currents (ACC) have been observed recently for LDPE and polytetrafluoroethylene (Teflon FEP). The paper reports on the ACC and ADC measured in the two materials at various temperatures, field strengths, for nonconditioned and conditioned samples, in a vacuum or ambient air conditions. The ADC is almost the mirror image of the ACC. Three characteristic zones have been identified, which are mainly determined by dielectric polarization, bulk conduction mechanisms, electrode effects and charge diffusion. The measurement of ACC and ADC can be used as a valuable technique for studying the charge transport and trapping mechanisms in correlation with the bulk and electrode effects. The upper limit for the drift mobility for LDPE at 80°C and 1.5 MV m^-1 was estimated to be 3.5×10^-13 m²V^-1s^-1 and for Teflon, at 140°C and 16 MV m^-1, to be 5.4×10^-16 m² V^-1 s^-1.