An assessment of the physical basis for the application of design criteria for dielectric structures

The use of design criteria for assessing the stresses to which composite dielectric structures are subjected implies careful and informed application. The convention required in the application of these criteria is examined in the light of the physical processes expected in an oil/cellulose transformer structure and related to an equivalent stressed-oil-volume theory of breakdown. The magnitude of the stresses implied by such criteria has been gauged from an examination of a number of case studies in which finite-element analysis has been used to determine the cumulative stress characteristic