Modeling of the effective permittivity of insulating presspaper

Effective permittivity model of insulating presspaper is built on the basis of the microstructure of the material. Due to the essentially layered structure in z-direction of presspaper, air voids inside the mixture can be treated as right prismatic inclusions. Analytical formula for the prediction of the effective permittivity of insulating presspaper is derived. Interestingly, the derived formula equals to the mixing equation applied for dielectrics in series. Numerical simulation was used to validate the analytical results by considering the air voids as cubical inclusions. Results show a good agreement between the analytically and numerically calculated effective permittivity values. Furthermore, dielectric permittivity results of commercial kraft paper and laboratory-made presspaper at 50 Hz were measured and compared with modeled data. It turns out that the deduced results give a good accuracy for the effective permittivity determination.