Ultralow-frequency dielectric properties of EPR with filler

The dielectric properties in the ultralow-frequency regions of ethylene propylene rubber with fillers are studied. These are important materials, especially for electrical cables and wires in nuclear power generating stations. The dielectric parameters α, τ_o, and ∈_ro-∈_r∞ in the Cole-Cole equation are obtained by fitting the theoretical curve with the experimental results on the discharge current. The present polarization is caused by the interfacial polarization between EPR and the fillers. Assuming that part of the filler clusters and takes the form of spheroids, the relaxation time is correlated with the shape of the spheroid. The observed distribution of relaxation times is interpreted as being due to the dispersion of various shapes of spheroids. As the concentration of filler increases in the low-concentration region, the characteristic relaxation time τ_o decreases. The decrement of τ_o can be understood with the variation of the cluster shape with the filler concentration