Partial discharge patterns in polypropylene and polyethyleneterephthalate films

Phase-resolved 3-dimensional partial discharge (PD) patterns D(n,q,φ) were obtained for samples of polypropylene (PP) foil and polyethyleneterephthalate (PET) foil at increasing and decreasing test voltages. A computer-aided measuring system was used for the registration of PD quantities in real time. The characteristics of the total PD number versus test voltage appear to have higher values at increasing than at decreasing voltage, which is observed as a hysteresis loop. The slopes of these loops depend upon the foils (PP, PET). The possible reasons of the disappearance of PD pulses are discussed