Space charge formation and physicochemical properties of aged XLPE cable insulation

The influence of different aging modes on the space charge accumulation properties and physicochemical properties of insulating materials in cross-linked polyethylene (XLPE) cables was investigated. The XLPE samples were obtained from unaged cables, 1-year laboratory accelerated aged cables and 30-year practical cables. Pulsed electro-acoustic (PEA) technique was used to measure the distribution of space charge in the insulating materials. Fourier-Transform Infrared (FTIR) and Thermo-gravimetric analysis were used to reveal details of their physicochemical properties. It was found that homo-charges accumulated at the Al electrode for the unaged cables, while the hetero-charges for aged cables. It was also found that the charge accumulation rate of unaged cables is highest, that of 30-years practical cable is second, and for the accelerated aging cables for 1 year, the rate of charge accumulation is lowest. It was also found that a new absorption peak appeared in the aged XLPE cables comparing with unaged cables. The hetero-charges appear to be intimately related to the ionization of aging products, injection and transportation of charges.