Critical examination of the life models for electrical insulationunder combined stresses in the light of the boundary conditions

摘要

The combined life models for insulating materials and the boundarynconditions that must be satisfied for their mathematical correctness arenexamined. In the case of materials with threshold, these considerationsnlead to the introduction of a lower limit gradient of electrical aging,nE_o, the existence of which is widely acceptable fromna physical point of view. In considering models for materials withnthreshold, the existence of a thermal threshold, which allows a newngeneral definition of such materials to be forward, is pointed out.nModels for materials with threshold in which the limit gradient En_o has been introduced are examined and theirnmathematical correctness verified. The existence of a threshold curve,nand thus of infinite electrothermal threshold couples, is emphasized