Understanding the Surface Discharge Characteristics with Thermally Aged Ester Fluid Impregnated Pressboard Adopting Fluorescent Fiber Technique

Surface discharge activity in transformers has an effect to permanently degrade the insulation structure. Early detection of these discharge is crucial for system reliability where Ultra high frequency (UHF) sensor and fluorescent fiber technique show good signal to noise ratio and better sensitivity. An accelerated thermal ageing is carried as per IEC 61125 at a temperature of 160°C. Surface discharge inception voltage (SDIV) and Phase-resolved partial discharge (PRPD) studies have been carried out for thermally aged natural ester oil impregnated pressboard (OIP), by adopting fluorescent fiber technique in comparison with the UHF technique. The optical emission spectroscopy (OES) identifies the emission spectrum of elements during the discharge activity, where a machine learning tool is employed to classify the specimens based on its ageing period. Further, characteristic variation in properties of thermally aged pressboard were analyzed through thermal analysis and solid-NMR studies.