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.