A Contribution to the Study of the Tracking Phenomenon in Solid Dielectric Materials uder 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 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 materials with different surface properties is shown; the influence on the drop volume is also taken into account. Oscillographic records of the tracking currents, as well as cinematographic and photographic records at different stages of the degradation phenomenon have been taken, in order to better clarify the behavior of the dielectric materials. The results obtained are discussed, and hypotheses of the degradation mechanism are suggested. A new line of research is indicated in connection with studies on flash-over phenomena concerning contaminated ceramic surfaces.