Intermittent load patterns can induce rapid cable temperature variations, which can induce supersaturation and then condensation of water at impurities in the insulation material during cooling. In this webinar we present results from experiments studying the effect of temperature cycling on water tree ageing in a homo-polymer high voltage AC XLPE insulation intended for wet-design cables. The initial study, presented here, exposed the insulation to 60 thermal cycles between 50 and 90 °C, using a cooling rate of 1 °C/min. In the second part of the study, ongoing now, identical test objects are exposed to a slower cooling rate; 60 thermal cycles between 50 and 90 °C with a cooling rate of 0.05 °C/min. Simultaneously, reference test objects at constant temperature are aged at the same applied electric fields. The degree of ageing is assessed through water tree analysis and breakdown testing.
Torbjørn Andersen Ve, Research Scientist, SINTEF Energy Research