Evaluation and comparison of unaged and field aged moisture impervious medium voltage cables

Electrochemical treeing is known to be a major cause of failures in cross-linked polyethylene cables. One method of preventing treeing is a moisture impervious layer on the cable. The on-core moisture impervious cable design is commercially available and has a large installed base. Much research has been done in the laboratory on the moisture impervious cable but little testing of field-aged cables has been done. The first phase of an ongoing test program of field-aged moisture impervious cables is described. Samples were removed from field service at a US electric utility in order to begin evaluation of field-aged cables. Also tested were new (1990) and unaged (1984) samples of the same construction as a control. AC high voltage breakdown, lightning impulse breakdown and switching impulse breakdown were performed. Also, material analyses were performed for comparison. These tests were begun in order to develop a database to demonstrate the long-term performance of on-core moisture impervious cables. The results from these preliminary tests indicate that on-core moisture impervious cables perform well in the field