Effect of interfaces on surface potential decay on double layered HTV silicone rubber samples

Interfaces between materials constituting composite HVDC insulation systems are typically associated with abrupt changes of the materials' dielectric properties, which cause accumulation of interfacial charges. These may affect various processes in the insulation system, including dynamics of charge transport and electric field distribution as well as its flashover performance. In the present study, the influence of macroscopic interfaces between layers made of high temperature vulcanized silicone rubbers on surface potential decay characteristics is analyzed. It is shown by comparing results of measurements on single and double layered samples that the rate of the potential decay may be significantly changed (increased or reduced) depending on how the layered structure is designed. The performed analyses show that the observed features cannot be explained by means of classical Maxwell-Wagner model and introducing additional charges at the investigated interface is necessary to successfully model the experimental data. The presented discussion concentrates on defining possible sources of such interfacial charges.