Factors affecting the transition from a water tree to an electrical tree

Electric stress, voltage waveshape, temperature, contaminants and insulation resistance to oxidation have been analyzed as to their influence on triggering breakdown of a water-treed polymer. The transition from a water tree to an electrical tree is dependent on several factors, including voltage waveshape, and magnitude, temperature, the insulation/semiconducting shield interface, and possibly the oxidative state of the insulation. For field-aged cables and molded specimens, the electrical tree always initiated when the water tree had reached or was within approximately 200 mu m of the adjacent surface. Shorter duration overvoltages required higher voltages to cause breakdown. There was some overlap in the breakdown voltages caused by 250/2500 mu s impulses and 60 Hz. High temperature decreased the time required to initiate an electrical tree, possibly due to the increased oxidation that occurs at the higher temperature. No particular contaminant or contaminant concentration was found to correlate directly with the event of the transition from a water tree to an electrical tree.<>