Evaluation of insulating materials on the basis of electrical treeing and breakdown tests

To verify the influence on material characterization of certain kinds of test procedures, two different electrode configurations (able to provide uniform and divergent electric field) are compared. Two kinds of XLPE (cross-linked polyethylene) specimens have been prepared and tested: (a) flat specimens having 0.25- and 0.45-mm thickness; and (b) 25-×25-×3-mm slab specimens in which an Ogura needle has been inserted. An attempt is made to infer the characterization figures (namely the activation energy or life-line slope) obtained for XLPE tested by two kinds of arrangements. Tree inception and breakdown voltage values, measured by cells at divergent field and progressive voltage, are compared with those given by short-term life tests realized by cells at uniform field at constant and progressive voltage. The results confirm that different electrode configurations lead to obtain different results for endurance characterization of insulating materials