Measurement of electric field distributions in polymer insulating materials under high DC voltage stress

The development of electric field distributions in polymer insulating materials under high DC voltage stress as a function of time is discussed. The electric field distributions were measured by the acoustic step-wave probing technique. The acoustic step pressure was generated using piezoelectric transducers. This technique was applied to four kinds of samples: two types of polyethyleneterephthalate (PET), copolymers of tetrafluoroethylene and hexafluorophylene (FEP), and Teflon. From the results, differences in the shapes of distorted electric field distributions were clearly observed for each material. The accumulated charges in the PET and FEP were negative, but those in the Teflon were of both polarities. The magnitude of the electric field distortion was larger at a higher temperature