Tracking and Erosion Performance of Liquid Silicone Rubber HV composite in Housings

Liquid silicone rubber (LSR) materials have been applied since more than 20 years as elastomeric housing materials of composite insulators. Process technology and material formulations were developed to meet the high quality requirements that are necessary for HV outdoor applications. LSR rubbers are typically applied for housings of large composite hollow and longrod insulators typically manufactured with the injection moulding technology. In comparison to typical high temperature vulcanising (HTV) silicone rubbers, LSR rubbers are not or only slightly filled with Al(OH)₃. The mineral filler Al(OH)₃ is used standardly to set up the required tracking and erosion resistance of the rubber material. This paper resumes the excellent long-term outdoor performance of LSR rubber material grades that are specially adapted for HV outdoor applications. The performance evaluation is based on long-term service experience of insulators in the field in comparison to the results obtained from material tracking and erosion laboratory tests. Insulators after 20 years in service in heavily polluted environments were investigated regarding damages caused by tracking and erosion. In order to compare the field results to those of available material tests, the "inclined plane test" (IEC 60587) and the "low current arc resistance test" (IEC 61621) on slab shaped test samples were performed. Insulator designs were evaluated by means of the wheel test, the 1000 h salt fog test and the 5000 h test (IEC 62217) that were applied to model insulators. Erosion resistance of LSR material samples is quantified by the mass loss, erosion depth and erosion length. The inclined plane test procedure according to IEC 60587 with varied conductivity of the electrolytical test liquid was applied, in order to detect the critical range of erosion. A comparison to the quantitative tracking and erosion resistance of HTV (Al(OH)₃ filled) silicone rubbers that are successfully ap- lied for more than 30 years in HV outdoor applications is given.