If the hydrophobicity is lost, the second “defence mechanism” of the material anti-ageing properties must protect the insulator. This is preferably evaluated by tests investigating tracking and erosion performance.

In this respect, it is well-documented that High Temperature Vulcanizing (HTV) Silicone Rubber grades enriched with Aluminium Trihydrate outperform non-enriched grades with low viscosity such as Room Temperature Vulcanizing (RTV) and Liquid Silicone Rubber (LSR) grades.
While in the beginning, the amount of filler was of negative influence to the dynamics of hydrophobicity effects, today’s HTV materials combine excellent tracking and erosion performance with a fast recovery and short hydrophobicity transfer time.

Regarding the insulating behavior of composite insulators, the property of hydrophobicity is considered to be the most important factor. The dynamic processes of the hydrophobicity loss and recovery and their strong dependence on material (including basic formulation, filler, and additives) and on processing technology are fields of continuous optimization.

As an example, in CIGRE Working Group D1.14 scientific investigations have been executed, the aim of which is a procedure to quantify the transfer of hydrophobic properties into a defined pollution layer.

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