High-field dielectric property of polypropylene with superposition of ac and dc field

We have developed a new detection method of ac dissipation current and its waveform of dielectric materials around power frequency. Using this technique and applying ac ramp voltage, electric field dependence of tan/spl delta/ of nonpolar polymers just after ac field application can be evaluated. In this paper we state an advanced measuring technique of high-field dielectric properties with superposition of ac and de field. The relation between ac loss property and superposed ac and dc field magnitudes immediately after their application can be evaluated for each one cycle of ac field. Using this measurement technique, electric field dependence of tan/spl delta/ of an oxidized polypropylene (OPP) film and effect of the superposed dc field magnitude on the tan/spl delta/ are examined both at room temperature and at high temperature. Finally, the relation between ac loss behavior of OPP film and superposed dc field magnitude is discussed in terms of the space charge formation in the polymeric material. The rapid increase of ac loss in high-temperature and high-field region of dielectric materials can be analyzed by using this measuring system.