Investigation on inverse volume effect of syntactic foam under uniform dc field stress

This paper deals with the experimental investigation on a new insulation material called syntactic foam. Syntactic foam consists of hollow glass or plastic microspheres casted into a polymeric matrix material in order to obtain a foam-like structure. The investigations carried out focus on the dependency between breakdown field strength and the volume of the stressed material under dc field stress. Specimens of syntactic foam with embedded sphere electrodes and electrode distances up to 8 mm are investigated in a voltage step test until breakdown. For distances of 1 mm and 3 mm a well-known volume effect of higher breakdown field stress on small electrode distances is observed. For distances above 3 mm an inverse effect can be found. The determined characteristic - called inverse volume effect - is ascribed to the specific material structure of syntactic foam.