Additives for the inhibition of water trees and phenomenological aspects of water treeing

Water-trees result when polyethylene (PE) or cross-linked polyethylene (XLPE) is electrically stressed in a moist environment /l/. The experimental results do not present a unified picture and the literature abounds with at times rather controversial results regarding the influence of the electric field strength, the frequency, the type of electrolyte, the temperature and the insulating material. Apparently, the initiation and growth of water-trees are rather complex processes which are influenced, in addition, by boundary conditions such as the type of sample used, the method of sample preparation and the selection and combination of stressing conditions. For this reason, we concerned ourselves in particular with defect sites at which the trees originate, with structural aspects of these trees, and with conditions relevant for initiation. Based on these phenomenological investigations a model of water tree formation was developed and used in the search for water tree inhibiting additives.