Trap Characteristics and Space Charge Behavior of High Voltage XLPE Cable Insulation

To estimate the aging state of the cross-linked polyethylene (XLPE) insulated cables with different service lives, samples were made from the XLPE insulation of six 110-kV cables, including one new cable and five aged cables with different operating years. The surface potential decay and trap distribution of XLPE samples were measured using the isothermal surface potential decay (ISPD) method. Then the space charge dynamic characteristics of XLPE samples were tested using the pulsed electro-acoustic (PEA) method. The results show that the surface potential decay of the aged cables is faster than that of new cables, the trap energy level decreases, and trap charge density increases after a long time of operation. In addition, the polarity and accumulation state of space charge are different inside the XLPE insulation of the aged and new cables. For new cables, the hetero-charges mainly accumulate near electrodes, while for aged cables, a small quantity of homo-charges are injected and accumulate near electrodes. The trap and space charge characteristics can reflect the aging state of XLPE insulation and their conjoint analysis can go deep into the aging mechanism and guide the status evaluation of the high voltage cables in service.