The Effect of ATH and Silica on Tracking and Erosion Resistance of Silicone Rubber Compounds for Outdoor Insulation L. Meyer 1,2 R. Omranipour 1 S. Jayaram 1 E. Cherney 1 1 – University of Waterloo – Waterloo - ON – Canada 2 – University of Blumenau – Blumenau – SC - Brazil Abstract: In this work, the influence of particle size and concentration of fillers used in silicone rubber compounds for outdoor insulation is investigated. Alumina tri-hydrate and silica with mean particle sizes of 5 and 10 µm are used as fillers with concentrations of 10, 30 and 50 % by weight in a two-part room temperature vulcanized silicone rubber base polymer. The results from inclined plane tests show that samples with high concentrations of filler and/or smaller particle size have better tracking and erosion resistance than samples with lower concentration and/or larger particle size. INTRODUCTION Today, non-ceramic or composite outdoor insulators are increasingly gaining a larger portion of the market over traditional ceramic insulators [1, 2]. The superior performance under humid and polluted conditions along with lightweight and lower cost are the main benefits from using non-ceramic insulators [3]. However, non-ceramic or polymeric insulators have relatively low resistance against tracking and erosion, when compared to ceramic insulators. Because of this, their long-term performance is still being investigated [4]. On the choice of a polymeric material suitable for outdoor insulation, silicone rubber has shown superior performance when compared to other materials for external housings of insulators, surge arresters and bushings. Since pure silicone rubber shows little tracking and erosion resistance, fillers like alumina tri-hydrate (ATH) and silica are added to the silicone rubber formulation. ATH and silica are the two fillers that are mostly being used by manufacturers of outdoor insulation. These fillers not only improve the tracking and erosion resistance but also lower the cost of the materials. In general, it has been reported that the type of filler [5], the amount of filler and particle size have an influence on the tracking and erosion resistance [6-8]. However, some confusion exists in this regard as often the comparisons have been made with unknown filler size and base materials. A proper comparison requires ATH and silica have to be used with the same base material to compare the relative influence of filler material on tracking and erosion resistance. In this context, the present work looks at the effect of ATH and silica on the performance of a two-part, room temperature vulcanized (RTV) silicone rubber considering similar particle size for filler materials and their concentration. EXPERIMENTAL To assess the tracking and erosion resistance, the inclined plane test (ASTM D2303 / IEC 587) [9,10] is used. However, instead of computing the time to track or time to erode, the time was kept constant (4 hours) and the degree of damage is evaluated by measuring the eroded volume of samples after the test. Tests were conducted with two types of fillers of two different mean particle sizes and three different concentrations. All concentrations reported in this paper refer to concentrations by weight. Two-part room temperature vulcanized (RTV) silicone rubber was used to prepare the test samples. The base polymer material consists of about 70% vinylpolydimethylsiloxane and 30% vinyl resin. Commercial silica and ATH having mean particle sizes of 5 and 10 µm sizes are used as fillers with main polymer. Test specimens and Setup The silicone rubber and the fillers were thoroughly mixed. After the addition of the curing agent, the mixture was stirred again, poured into a mold and degassed. Six samples were prepared for each compound. Samples were cut into dimensions as specified in the ASTM D2303 standard. The thickness of the sample was 7 mm (+/- 0.5 mm), which allowed easy handling and fixture on the sample holder. The test setup was assembled following the standard, and is shown in Fig. 1. A computer data acquisition system was used to record the leakage current and voltage across each specimen separately. Figure 1: Main components of the inclined plane test setup.