Test methods useful in selecting materials for outdoor high voltage insulation

The availability of acceptable outdoor insulators that will meet the electrical and mechanical requirements for EHV transmission systems presents a complex and unsolved problem. A considerable effort has been spent toward developing a single material with suitable mechanical strength and long-term insulating stability. The unlikelihood of finding such a material has prompted the concept of a composite insulator where two materials are combined to perform the total insulator function, one for mechanical strength and the other for surface stability and long term electrical insulation. This paper deals with the electrical insulating function and classification of materials best suited for outdoor insulators based on their surface behavior in a high voltage and simulated wet, outdoor environment.