Aging of silicone rubber composite insulators on 400 kV transmission lines

A number of silicone rubber composite insulators have been examined following 15 years of service on a coastal 400 kV transmission line in the UK. Extensive measurements of their hydrophobicity, as determined by contact angle, are given along with a description of their appearance. The hydrophobicity change varied from the low voltage end to the high voltage end with the lowest contact angles being found in the middle of the string. The sheds also aged differently around their circumference and this was reflected in discoloration differences on different sides of the insulator, in addition to hydrophobicity changes. The greatest change to properties was witnessed on the core of the insulators on which contact angles of less than 70 degrees were recorded