The role of cations in water tree growth in technical grade XLPE insulated cables

XLPE insulated cables were subjected to heat cycling in the presence of electric stress and aqueous ionic solutions composed of NaCl, Cu(NO3)(2) and CuSO4. The results displayed a large water tree propensity index due to the sulphates. To evaluate contribution of cationic and anionic parts of salt compositions, trees were grown in solutions containing a fixed anion (SO4--) but different cations with valences of +1(Na+, K+), +2(Cu2+) and +3(Fe3+). These results showed that cations play a dominant role in the initiation of water trees. Different recent models which propose that tree generation is based on the ionic nature of chemical species, were tested in the light of present results and were not found fitting. Instead it is proposed that it is the physical and electrochemical nature of elemental part of salt particle, which plays the dominant role in reactions that cause degradation of the polymer in the presence of applied electric field.