High voltage characterization of high dielectric constant composites

Recent advances in the development of high energy storage composites at the University of Missouri-Columbia have resulted in the production of thick materials with a dielectric constant greater than 125 at frequencies on the order of 100s of kHz to at least 4.5 GHz. Since the composites were developed for high voltage devices, they were fabricated with a thickness on the order of millimeters. The highest priority in optimizing the composite properties was to maximize the dielectric constant. However, to ensure compatibility in repetitive pulsed applications, the dielectric losses were minimized, and the dielectric strength was maintained on the same order as conventional insulators. The high dielectric constant composites are characterized by five methods under low and high voltage conditions. The complex permittivity is measured from 100 kHz 30 MHz and 200 MHz 4.5 GHz using industry-standard methods and equipment at low voltage. Additionally, four custom high voltage diagnostics were designed and constructed for high voltage characterization. First, a high voltage pulser is implemented to determine the dielectric strength of the composites under pulsed conditions. Second, the electric field dependence of the composite polarization is measured with a modified Sawyer-Tower polarization test stand. Third, small high voltage capacitors constructed from the high dielectric constant material are characterized by examining the resonance of a high voltage underdamped discharged at a frequency of 10s to 100s of MHz. Lastly, the material is evaluated as a high voltage transmission line using time domain reflectometry techniques. The diagnostic methods used to characterize the dielectric materials are described with an emphasis on the high voltage techniques and data from selected diagnostic methods are presented.