Dielectric properties of nonlinear grading materials: Measurement and computation

Nonlinear grading materials, i.e., materials for which the electrical conductivity and/or dielectric constant is a function of the electric field and temperature, are being used increasingly in advanced high voltage accessories. The ability to design with such advanced materials requires programs for transient non-linear finite element analysis, which have been used in research for over a decade and are now available commercially. However, the use of such programs requires good knowledge of the nonlinear dielectric properties of the grading materials as a function of electric field and temperature, and systems for measurement of such nonlinear properties have not been developed. ^ The theory of dielectric property measurement has been developed for such materials, and a system has been designed and implement for measurement of nonlinear dielectric properties. The system is based on application of a high voltage impulse and measurement of the current through the sample as a function of time during the impulse. As the current is measured at the same voltage but with different derivative of the voltage with respect to time on the rise and fall of the waveform, the electrical conductivity and dielectric constant can be determined as a function of applied voltage (or field) during the waveform. The measurement is limited by the relative magnitude of the resistive and capacitive currents, the ability to predict the voltage waveform accurately, etc., and these issues have been addressed in the theory of measurement developed in this thesis.