Investigations on the dielectric properties of syntactic foams and the change of their dielectric properties due to water immersion

Syntactic foam is a light weight high voltage insulation material that consists of micro-scale hollow particles, so called hollow microspheres (HMS) embedded in a polymeric matrix. The material properties of this hybrid material can be customized to special needs concerning the required properties. For outdoor applications the independence of the properties of insulation materials on the presence of water is necessary. Therefore the dielectric properties of syntactic foam and their behavior when immersed in water are investigated. Plate specimens of 3 mm thickness are stored over a period of 50 days in deionized water tempered to 50 degrees C for the purpose of accelerated water absorption. The relative permittivity as well as the dissipation factor of various compositions of syntactic foam before and after water immersion are compared. The foam compositions vary in the matrix material and the HMS shell material. Further, the compositions vary in the filling degree as well as the HMS diameter. Hence, the influences of these parameters are also investigated. It is observed that the change in the dielectric properties of syntactic foam due to water ingress depends on the polymer matrix, the filler type and the filling degree.