Condition evaluation of MV XLPE cable with steprise breakdown and relaxation current method

Crosslinking polyethylene (XLPE) insulated medium voltage (MV) power cable is widely used in power transmission and distribution areas and its reliability is very important to the power utilities. In order to assess the cable status effected by production process, material used and installation conditions, 6 types of 10 kV XLPE cable samples were manufactured and experimentally aged with full loader for one year in water and in the air, respectively. After that step-rise breakdown test was carried out to characterize the aging degree of those cables. It is shown that the insulation material is the key factor determining the original cable status, and manufacture process also influences the original status to some extent. It is verified by the breakdown strength that cables laying in the water aged more greatly than those laying in the air. In order to analyze the aging results theoretically, the isothermal relaxation current (IRC) method were carried out on cable samples with different aging stages. It is shown that the aging factor deduced from the IRC currents has a strong relation with the insulation used. At the same time, it could be seen that the aging factor increment differs from each other. It was strongly verified that insulation must be the key factor to determine the cable´s quality and life time, and the manufacturing process influences the life time to some extent. Finally, it could be concluded that IRC, which is a non-destructive assessing technology, can be used to evaluate not only aging degree, but also the original quality of cables.