The Effect of Service and Test Conditions on Water Tree Growth in XLPE Cables

Experimental studies of tree growth are often performed under one single set of test conditions. The aim of this work has been to systematically vary the test conditions to study their influence on tree growth in one type of XLPE cable. It was found that water in the conductor dramatically increases the number, size and growth rate of trees. In such tests the temperature of the outer screen should be controlled as well as that of the conductor, because the temperature gradient determines the degree of supersaturation in the insulation wall. Stationary temperatures are found to cause more severe tree growth than cycling temperatures. This is contrary to the situation with dry conductor where cycling of both the conductor and outer screen temperature greatly enhances tree growth.