Characteristics of electrical treeing in extruded polypropylene and cross-linked polyethylene cable insulation

This paper presents results from experimental investigations performed in order to characterize and compare electrical tree formation in extruded syndiotactic polypropylene (s-PP) and cross-linked polyethylene (XLPE) cable insulation. All tests were performed using molded needle-plate samples with an insulation distance of 1.05 mm. Initiation and formation of electrical trees from the needle tips were studied using partial discharge measurements and optical microscopy video techniques. The tree growth was characterized by measuring length and width of the trees, the time needed for the first branch to reach the opposite ground electrode and time to electric breakdown. The effect of different AC voltages, with magnitudes up to 12 kV and frequencies in the range of 50 - 1000 Hz, were examined.