Performance of synthetic insulating materials under polluted conditions

Both the dust/fog and IEC methods have been used to investigate the resistance to surface tracking and erosion of a range of synthetic insulating materials under polluted conditions. The relative merits of these test methods are discussed, and reasons given for preferring the dust/fog test. Consideration is also given to methods of accelerating the dust/fog erosion test. Results of such tests have been considered from a theoretical aspect, and a relationship between chemical structure and resistance to surface tracking is proposed. Using this approach, it was deduced that the alicyclic epoxy resins would be superior to the conventional bisphenol-based resins; this has been confirmed by dust/fog tests. Tracking resistance can also be increased by use of fillers, and this is illustrated for silica and alumina trihydrate in some epoxy casting systems. The application of track- and erosion-resistant materials to service use is considered, with special reference to casting resins. It is shown that the use of fillers to improve track resistance may cause deterioration in other electrical and mechanical properties of the material.