To study the influences of acidic environment or alkaline environment on the growth of water trees in XLPE cables

XLPE cables were placed under different p H environments to carry out water tree aging experiments. After the aging of water trees

the microscopic morphology of water trees under different aging conditions was observed and compared by using an optical microscope

and lengths of water trees were counted. The results show that acidic environment and alkaline environment are beneficial to the growth of water trees. The average lengths of water trees are in th

e following order: L

av

（pH=1）>L

av

（p H=13）>L

av

（pH=5）>L

av

（pH=9）>L

av

（pH=7）. The water trees which grow in the neutral environment（pH=7） are deeply dyed and the branches are obvious. In acidic environments（pH=1

pH=5） and alkaline environments（pH=9

pH=13）

the water trees areas are lighter and the branches are indistinct. A possible explanation is given for the above experimental results from the viewpoint of ionic nature. Ions play an important role in the growth of water trees. Hydrogen ions and hydroxide ions in aqueous solutions have special migration patterns. Their ion mobility is much larger than that of general ions. They are more destructive to material chemical bonds and molecular chains

and they cause more serious aging of the water trees. The ionic radii of sodium ion and chloride ion are larger

and the cracks and holes formed after the fracture of the XLPE molecular chain are larger

resulting in deeper staining in the water tree region.