To investigate the changing characteristics of the polarization and depolarization currents（PDC） branch parameters of water tree aged cables

we analyzed the microstructural characteristics of the water trees

and revealed the influence of the microstructures of water trees on the PDC branch parameters. Short and long cable samples were subjected to an accelerated water tree aging. The polarization and depolarization currents of the samples were tested by the PDC method

and the Debye model branch parameters of the aged samples are calculated. The water trees in the short cable samples were observed by a microscope

and the microstructures in water tree regions were observed by a scanning electron microscope（SEM）. The identification results of the PDC three branch parameters show that the time constant of the third branch of water tree aged samples is significantly higher than that of the unaged samples. In addition

the increment of the capacitance is higher than the decrement of the resistance. The microscopic observation results show that there are numbers of isolated microvoids in the water tree regions. It is analyzed that water tree propagation can result in the fracture of the XLPE molecular chain segments and the formation of large numbers of interfaces between microvoid and XLPE

thus both the dipole polarization time and the interfacial polarization time increase

and the polarization time constant of the third branch increases. In addition

there can be large numbers of isolated microvoids in the water tree regions

which inhibit the movement of the ions in the water tree regions

thus resulting in the higher increment of the capacitance than the decrement of the resistance of the third branch.