Insulation characteristics of epoxy insulator with internal crack-shaped micro-defects - study on the equivalence of accelerated degradation by frequency acceleration test. - Ueta, Genyo; Wada, Junichi; Okabe, Shigemitsu; Miyashita, Makoto; Nishida, Chieko; Kamei, Mitsuhito (IEEE Transactions on Dielectrics & Electrical Insulation, 2014)