Novel specimen design to test engineering plastics for power electronic applications

The paper presents the development of a novel test specimen design for engineering plastics, which allows stressing the insulating materials with electric field strength under various environmental conditions over an extended period of time. The specimen design enables simulating long-term behavior under electrical stress at simultaneously intensified external loading situations. Thus, it becomes possible to quantify engineering plastics for the given environmental conditions in use. The study contains a quality evaluation of the injection molded test specimen. Furthermore the influence of the electrode arrangement, distance and surface roughness on the homogeneity of the electrical field between the electrodes and the resulting breakthrough behavior of engineering plastics will be discussed. Beside design aspects, the microstructure of glass-fiber and glass-sphere reinforced thermoplastics, typically used as housing materials in power electronics, is correlated to their electrical behavior under the influence of humidity and temperature using the novel test specimen design. The results show how the microstructural composition of the plastics, such as type, amount and size of filler particles or micro defects like gaps between glass-fillers and the polymer matrix, influences the dielectric strength of engineering plastics.