Outdoor insulation housings

Silicone rubber and EPDM compounds are widely used to build outdoor insulators such as cable terminations and line insulators. These materials undergo the simultaneous effects of electrical stresses (corona, arcing) and climatic environmental stresses (UV, pollution, rain). It is important to test the performances of these materials and predict their long term behavior. Three specific properties are selected as important features of these outdoor insulating materials: (i) The resistance to erosion and tracking when submitted to dry band arcing. (ii) The time before losing hydrophobicity when submitted to a wet environment (fog, rain). (iii) The speed of the hydrophobicity transfer to a pollution layer. Three specific tests are developed to independently measure these three characteristics. They are respectively based on: (i) Measurement of the eroded volume of material submitted to controlled dry band arcing. (ii) Surface conductivity measurement after submission to rain for lengthy periods. (iii) Contact angle monitoring of the pollution layer hydrophobicity. This paper describes the tests and presents some results conducted on silicone rubber materials. This work yields physical criteria which allows us to classify different formulations with regards to their application as outdoor housings