In order to realize fast and effective diagnosis of the insulation aging problem of 10 kV cross-linked polyethylene（XLPE） cables

we analyzed the low-frequency dielectric loss characteristics of degradation cables based on the short-time polarization and depolarization current（PDC） method

and proposed a diagnosis method of cables for different aging types. According to the cases that the actual operation cables may occur

the short and long cables were manually accelerated aging in the laboratory. Based on the theory of dielectric response

the low-frequency dielectric loss characteristics and the asymmetry of polarization and depolarization current were analyzed for the laboratory cables before and after aging. At the same time

to further verify the effect of this diagnostic method on assessing the actual operation aging cables

the field-aged and in-service cables of which the aging states are known were collected

and the polarization and depolarization current tests were also performed. The results show that the low-frequency dielectric loss spectrum not only can detect the bridging water trees in the cable insulation

but also can diagnose the humidified insulation and the large-but-short water trees in cable insulation. It is not difficult to find that the dielectric loss factor of polarization current is usually greater than the dielectric loss factor of depolarization current for the cables with concentrated defects. And as for the overall insulation degradation

the dielectric loss factor of polarization current is not greater than that of depolarization current. The diagnosis results based on laboratory-aged cables and field-aged cables confirm that the low-frequency dielectric loss spectrum and its asymmetry can accurately reflect the different types of aging of cable insulationn.