Introduction: Composite insulators are now deployed throughout the world and are steadily replacing traditional ceramic and glass insulators. Low weight and physical robustness are two properties which have led to an increasing market share for composite insulators over the last 20 years. However, there is concern over the long term ageing of these insulators.

This work has characterised the millimetre scale arcing activity between water droplets and developed an experimental knowledge and theoretical understanding of how this leads to macroscopic behaviour. In particular, it identified the local surface conditions on the millimetre scale which cause the ageing of hydrophobic material surfaces.

Objectives: Develop reliability models for hydrophobic insulators, recommend test schedules for type approval and product development and identify condition monitoring techniques for existing installations.