Material differentiation by water treeing tests

Because of the importance of water treeing in underground medium voltage cables and the interest in preventing it, many accelerated material test methods and tree retardant materials have been developed. In this paper, several accelerated material water tree tests are reviewed. Three commercially introduced tree retardant materials were evaluated by the ASTM D6097 water treeing test under various conditions. The test parameters included aging time, temperature, water conductivity, applied voltage level, and frequency. As expected, the length of water tree increases with these factors, except temperature. Temperatures, higher than end use conditions should not be used as an acceleration factor. Not all tree retardant materials have the same water tree retardance, since each tree retardant material shows different response to the test parameters. A good tree retardant material should be very effective at various aging conditions. A higher water conductivity or longer aging time is recommended for better material differentiation in the ASTM D6097 test.