Decay products in mineral oil: A comparative study between hybrid and conventional insulation systems

The useful functional life of a power transformer is determined by the life of the paper insulation. Therefore polyaramid based synthetic insulation paper, with better thermal stability emerged for application in transformers. In this research work, the quality of mineral oil aged with hybrid solid insulation is investigated. Comparison was made with traditional mineral oil impregnated cellulose paper to provide base line for comparison. The samples underwent thermal accelerated aging procedure according to ASTM-D1934 standard. The aged samples were furthermore submitted to local overheating. The condition of oil samples collected from each aging vessel was assessed using several diagnostic techniques, namely the dissolved decay products (DDP), the insoluble decay products (Turbidity), the interfacial tension (IFT) and the moisture content. The results indicate that oil aged with hybrid solid insulation depicts less dissolved and insoluble decay products and less polar contaminants at some aging stages especially after the application of a local overheating.