To reveal the influence of ion properties on the water tree propagation characteristics of AC cross-linked polyethylene（XLPE） power cables

the microstructures of water trees aged in different solutions were observed

and a possible mechanism was presented to explain how ion migration affected the water tree propagation. Accelerated water tree aging experiments were performed in NaCl and KCl solutions（0.1 mol/L）. The water tree structures were observed by optical microscope and tested by infrared spectrum（IR）. Electric field simulation was established using the real data of water tree structure. The results show that water trees in NaCl solutions are longer and thinner with small micro voids than those in KCl solutions. Water trees in NaCl solutions are aged more seriously than those in KCl solutions by means of IR. There is field shielding phenomenon in water tree regions. The electric field inside water tree is much lower than that at water tree branch tips and border. The electric field simulation results show that the electric field of water tree branch tips aged in NaCl solutions is greater than that in KCl solutions. In the XLPE material

sodium ions migrate faster than potassium ions. Consequently

water trees propagate faster in NaCl solutions. Therefore

the size of micro voids and water tree branches are limited to the speed of water tree propagation. So water tree branches are thin with small micro voids in Na Cl solutions than those in KCl solutions. In the same ionic concentration

fast ionic migration induces long water tree

small micro voids and thin branches.