Effect of ageing conditions on the type of water treeing [powercables]

A concept is presented that can serve as a tool in discussions of the improvement of materials and tests to prevent water treeing in underground power cables. It describes the ways in which ageing conditions, processes, and degradation characteristics are related. The concept is based on an extensive collection of experimental data, which show that water trees grown under different conditions have quite different compositions. Since the degradation products differ fundamentally, it is concluded that different water tree growth processes take place. Three principles for reliable testing are discussed in relation to the present concept of water treeing. The principles concern the correlation between test results and breakdown strength reduction in service, obtaining results in a reasonable amount of time, and obtaining sufficient accuracy