DEVELOPMENT OF NEW DEGRADATION DIAGNOSIS METHOD OF OUTDOOR INSULATION USING AC DISSIPATION CURRENT WAVEFORM MEASUREMENT

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Development of new degradation diagnosis method of outdoor insulation using AC dissipation current waveform measurement has been studied. The new measurement system with DSP can evaluate dielectric property of a sheet type sample. The electric field dependence of dielectric property can be evaluated simultaneously with electric field application. The transfer function of the system is also evaluated automatically by the DSP system. By using DSP system, applied voltage waveform is controlled and the system can cu off the applied high. voltage within next one cycle of field application in case of abnorma response. This system can detect time varying property such as surface conductivity during wetting or drying of silicone rubber sheets.Water absorption reduces the hydrophobicity of silicone rubber. The recovery of the contact angle has two stages. Initially it recovers quickly that is related to the evaporation of absorbed water. After this quick recovery it increases slowly that seems to correspond to the LMW or the silicone surface.Both U-M (Bulk direction ; High voltage to Main electrodes) and G-M (Surface direction : Guard to Main electrodes) application of electric field can detect the changes in dielectric property during aging and recovery of the silicone rubber sheets. HTV is more sensitive compared to RTV for studied conditions of aging and recovery.Dielectric constant of HTV silicone rubber increases during aging by water absorption and decreases during recovery in air by the evaporation of absorbed water. Tandelta shows simple increase during 1st aging, however, it shows like an interfacial polarization during aging and recovery after certain amount of LMW has reduced from the bulk of HTV silicone rubber.