Stress relieving with resistive materials based on silicon carbide (SiC)

This article deals with stress relieving on components of high-voltage equipment with semi-conducting materials based on silicon carbide (SiC). By using SiC, non-linear resistance characteristics can be implemented. This is worthwhile where different operational states of a stress-relieving layer have to be implemented, e.g. in the case of housings for high-voltage fuses. Such housings 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 layer is of special interest, because it must comply with different tasks: When the fuse is in normal operation, the stress relieving must prevent partial discharge (PD) inside the fuse. If the fuse is open, the remaining current through the inner 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 mastics 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. will be presented. Finally the long-time behavior of these materials compared to materials already used in cables and cable accessories will be shown.