Interfacial phenomena in composite high voltage insulation

This paper deals with two different types of composite insulating materials for HV outdoor insulation technology. For outdoor applications fiberglass reinforced polymer (FRP) is used mainly in transmission line insulators (composite long rods), and as power apparatus housings (composite hollow core insulators). During the last decade mineral filled polymer (MFP) was found to be very suitable for outdoor insulation in the medium and HV ranges. To meet the outdoor demands, long-term stability and durability against environmental stresses are necessary. Composite insulation consists of more than one dielectric component, and linking at least two different kinds of materials leads to interface problems. These regions always appear as weak material structures that can be attacked by various aging mechanisms. The long-term performance and aging resistance are determined by the interface quality. One can distinguish four principal kinds of interface: microscopic, e.g. those between fillers and matrix components; macroscopic, e.g. those between glass fiber rod and polymeric shielding material; internal, in the insulation bulk; and external, solid surface against a liquid or gaseous phase. Today the use of composite insulating materials in HV technology is state of the art. They offer a wide range of superior properties for indoor as well as for outdoor applications. Further improvements should focus on the hydrophobicity and on the long term resistance of the external interface and the stability of the internal interface