The validity of the mechanical damage theory of water treeing tested against experimental results

A brief review is given of the mechanical damage theory. It assumes that a tree-branch may be considered as a conductive needle-shaped droplet. Field enhancement at it's tips leads to mechanical stresses high enough to cause rupture and further tree growth. Treeing is thought to start from hydrophilic or microporous particles or from cracks around microvoids were a high hydrostatic pressure develops due to osmotic pressure or a slight supersaturation of dissolved water in the polymer.