A contribution to the study of the tracking phenomenon in solid dielectric materials under moist conditions

IEC/TC15 is preparing a new edition of Publication 112 concerning a method for determining the comparative tracking index (CTI) of solid insulating materials under moist conditions; the Electrical Engineering Dept., University of Genoa, has performed a set of tests on this subject. A short description of the aims, of the procedure and of the apparatus used for the tests reported in IEC Publ. 112 is given. Several metals have been used for the electrode system to investigate their influence on the tests, and the relevant results are reported. Solutions of different kinds of contaminants have been employed to study particularly the action of wetting agents. Ionic and non-ionic wetting agents have been used, and their effect on solid insulating materials with different surface properties is shown; the action on the drop volume is also taken into account. Oscillographic records of the tracking currents, and photographic records at different stages of the degradation phenomenon have been taken in order to better clarify the different behaviours of the dielectric materials. The obtained results are discussed, and hypotheses on the degradation mechanism are suggested.