Toward a Credible Aging Test for Extruded Cable

The introduction of extruded cable designs claiming resistance to water treeing has generated a need for valid accelerated aging tests to evaluate such claims. However, some of the phases of the water-treeing failure process (water permeation, water-tree initiation and growth, final breakdown) are not yet completely understood. Accelerated tests proposed to date may not affect these aging sub-processes in the same way for different cable designs, and consequently such tests may yield misleading results. To simulate the entire aging process, a separate accelerated test for each of the sub-processes may be more practical than a single comprehensive test. Neither a comprehensive test nor a collection of separate tests can be developed into a universally valid accelerated life test until the treeing process itself is better understood. Inherent limitations of various approaches to the development of accelerated aging tests are discussed and the conclusion is drawn that progress may be most economically achieved by fundamental or analytical approaches, rather than by purely statistical studies.