Space charge injection in polymers: New experimental results

For a long time treeing has been known as a major mechanism responsible for ageing of technical insulations, which can subsequently lead to their catastrophic breakdown. According to its importance, treeing is the subject of a vast number of publications /1/. Tree initiation and the conditions for tree growth, however, have been studied to a much lesser extent. In a recent paper /2/ this problem is treated phenomenologically in analogy to classical fracture mechanics /3/. An electro-mechanical fracture criterion has been introduced, stating that a tree can only grow if the release of electrostatic energy is larger than the mechanical deformation energy needed to form microchannels, i.e. trees.