Impact of cations toward the water tree propensity in crosslinked polyethylene insulation

Technical grade crosslinked polyethylene (XLPE) cable’s insulations 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 show 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 sulphate anion but different cations with valences of +1(Na+, K+), +2(Cu+) and +3(Fe+). The results of tree lengths show that cations play an important role in the growth of water trees. Different models which suggest that the water tree generation is based on the ionic nature of chemical species are examined in the light of present results and it is suggested that the physical and electrochemical nature of cations play an important role in the reactions that cause degradation of the polymer in the presence of the applied electric field.