Measurement of resistive and absorption currents in capacitor films up to breakdown

An electronic system with active feedback has been developed to facilitate measurement of resistive currents in polymer films up to breakdown. The system cancels the capacitive current actively to facilitate the measurement of the resistive current. The measured current is the result of the very rapid relaxation from a capacitive field distribution to a resistive field distribution at very high fields approaching breakdown. If the material were truly homogeneous, the resistive and capacitive field distributions would be the same. Most polymers are semicrystalline, with crystallites which have much lower conductivity than the amorphous regions with the result that the capacitive and resistive distributions are not the same. Absorption current data up to breakdown (~700 V/m) are presented for biaxially oriented polypropylene (BOPP) made by both the tenter and bubble process. These data are compared with measurements of polystyrene capacitor film which is amorphous. Transient nonlinear finite element analysis computer simulations are presented in a companion paper