Comparison of Propensity toward Water Treeing in XLPE Insulated Power Cables Produced in Arab Gulf Countries

Electric power utilities and industrial units in Saudi Arabia and other gulf countries are extensively using XLPE cables produced in the Arabian Gulf region. Due to prevailing high temperatures and high sulphate and chloride contents in the soil coupled with high sub surface water table in some areas, these cables have suffered serious breakdowns in a relatively short time span after their installation. This investigation was undertaken to compare the resistance to water treeing of 15 kV, XLPE insulated cables produced by four regional cable manufacturers. In the first stage, aging was carried out using AEIC protocol under high electric stress and temperature cycling in the presence of deionized water. After 120 days of such aging, the retained dielectric strength of these cables was determined by high voltage time test. The results showed poor performance of one of the cables while the three others exhibited close values. In the second stage, the cables were aged in the presence of aqueous ionic solution of CuSO4 and elevated electric stress for aging periods that lasted in the range of 500 to 1500 hours. Water tree number and lengths were measured and were analyzed using Weibull and log-normal statistical distributions and were found to fit better on log-normal model. Furthermore, water tree density which varied as a function of aging period obeyed a log-linear relation. These data also show that for a fixed aging period, water tree density in these cables as evaluated in the second stage of aging, comparatively varies significantly and leads to a better method of discrimination between different cables in order to select a cable that will serve best in wet local environmental conditions.