Observation of AC surface discharge on insulating film by Pockels effect

In order to design the insulation of high-voltage equipment, it is necessary to develop a measurement method for understanding the time dependence of AC (50 Hz) surface discharge on an insulating material. The authors have developed a method by which one can obtain the surface charge pattern and density by means of an electrooptic Pockels effect in BSO (Bi₁₂SiO₂₀) crystal. They have improved the optical system to obtain the time dependence of the AC (50 Hz) surface discharge pattern and density on an insulating film. The observed AC charge distribution on a PET film surface is reported. The relationship between needle-film gap size and residual surface charge pattern is discussed