Field-grading with semi-conducting materials based on silicon carbide (SiC)

This article discusses field-grading of components in high voltage equipment with semi-conducting materials based on silicon carbide (SiC). One application is the housing of high voltage fuses (hv-fuses), where different constraints must be taken into consideration. Housings for hv-fuses may consist of a dielectric basic material with inner and outer conducting layers, where the outer layer is grounded and the inner layer is on high voltage potential. The inner conducting layer is of special interest, because it must comply with different tasks: When the fuse is in normal operation, the field-grading must prevent partial discharge (PD) generation inside the fuse. If the fuse is open, the remaining current through the inner conducting layer must be negligible. Two different types of conducting layers are discussed: one kind consists of a ceramic overglaze, the other is based on different organic matrixes like silicon rubber, epoxy resin and silicon resin. SiC was used in different quantities, qualities and grain sizes, affecting the behavior of the conductive layer. The influences of these parameters are shown. The electrical behavior of both types of conductive layers, in dependence of various parameters like different voltage levels, temperature etc. are shown, as well as a comparison of both types. A numerical simulation of the behavior is proposed