ELECTRICAL TREE INITIATION

This paper reviews the recent understanding of the initiation mechanis ms of electrical trees and the phenomena occurring during the inductio n period in the discharge free condition. The importance of charge inj ection in electrical tree initiation is well established, not only und er de or impulse stresses, but also under ac stress. Electroluminescen ce can be used as a monitor for charge injection. Tree initiation from field enhancing locations under moderate stress proceeds through cumu lative degradation reactions and cavity formation caused by injected c harge. The dependence of tree initiation on temperature and the nature of dissolved gases, underline the importance of free volume processes , and therefore of polymer morphology. Electron avalanche type tree in itiation is strongly influenced by field modification due to space cha rge and also by the size of the high field region.