Assessment of polyethylene based insulations for wet environments

There is much debate over methods used for testing medium voltage polymeric insulated cables for use without a moisture barrier. The proposals being considered by CENELEC for a European test involve ageing periods of long duration, up to two years. The cable is judged to pass if the breakdown strength is retained at a chosen level, or, if the test samples survive the ageing period. These tests will take more than two years to complete and report. Consequently there is a need for other assessments that could be used, possibly as sample tests, or even as pretest assessments. The author explores some of the factors that contribute to the test procedures and considers the prospects of quicker test methods. The author describes the role of temperature on the breakdown testing of tree retardant insulations; the influence of rapid temperature cycling on water tree growth; and the factors which influence vented treeing.