The effect of filler particle size on ultrasonic image of electrical breakdown region in filler-added insulating materials

The ultrasonic visualization method proposed provides an effective way to detect or visualize the electrical breakdown region in specimens of organic insulating materials even when filled with powder materials. However, there exist a few problems on ultrasonic visualization for such kinds of resins, mainly due to their peculiar acoustic characteristics, i.e. specific acoustic impedance, heavy signal decay within the material and scattering noises from filler particles. Above all, scattering noises prevent the formation of clear ultrasonic images of the electrical breakdown region. In this paper we report the dependence of filler particle size on the magnitudes of scattering noises reflected from filler particles, and recommend the use of filler materials with smaller particle size for convenient future insulation diagnosis