Influence of ageing conditions on water tree growth processes

The influence of aging conditions on the processes which take place during water tree growth in XLPE (cross-linked polyethylene) is examined, and how the characteristics of the water trees are influenced is considered. As a special case, an experiment is reported addressing the question of whether adapted needle tests on XLPE can simulate water treeing in service. It is shown that water trees grown under different conditions may have quite different compositions and therefore different properties. It is recommended that this fact be considered in the development of test methods. The chemical composition can be a measure of the significance of the test conditions. In particular, indications are found that a needle test may better simulate service ageing with a lower electric field, an oxygen flow, and the use of CuSO₄ as a catalyst for oxidation