Voltage Ramp-rate Dependence of DC Breakdown in Polymeric Insulators: Physical Models versus Data

The standard handbook values for dielectric breakdown strength of necessity come from accelerated test methods. In some cases, the breakdown voltage may vary significantly with voltage ramp rates; therefore, a theoretical model for the ramp-rate dependence of breakdown is needed to extrapolate from realistic tests to long-duration material service lifetimes. Series of step-up to breakdown tests were performed for ramp rates from 0.5 to 500 V/s for biaxially-oriented polypropylene (BOPP), low density polyethylene (LDPE), and polyimide (PI) films. The data were fit with standard empirical methods, as well as two physics-based defect-driven models. Empirical models can be fit to a given data set; however, they offer little—if any—physical insight. Voltage ramp rate can, in some materials, significantly affect the breakdown field. However, the physical models, one of which was successful in describing preliminary data, were shown to be inadequate for the other materials tested