Evaluation of high field conduction models of polymeric dielectrics

The image charge as measured with a guarded needle apparatus continues to increase for a time as the voltage drops after reaching its peak value, before leveling off to a relatively constant value. The increase of apparent charge beyond the peak voltage is the result of charge spreading in the dielectric even as the voltage decreases. Such spreading of charge is very sensitive to the slope of the conductivity with respect to the field in the region of the space charge limited field. Numerical simulations are employed to match the measured material properties to the simulated material properties for various functional relationships between the conductivity and electric field. Estimation of the field dependence of the conductivity in the region of the space charge limited field based on these computations is presented in this paper