Comparative study between conventional and hybrid solid insulation systems

A conventional mineral oil/cellulose insulated transformer´s functional life is limited by the life of the cellulose paper. Since cellulose paper aging is accelerated by temperature, moisture and oxygen, poly-aramid-based synthetic insulation paper, with better thermal stability, has emerged for use in transformers. Two ASTM tests methods: DP_V “degree of polymerization” as a direct diagnostic tool according to ASTM D4243 and DGA “Dissolved Gas Analysis” as an indirect diagnostic tool to quantify carbon oxides (CO and CO₂) according to ASTM D3612 were used to monitor the thermal aging of the cellulose paper within solid hybrid insulation aged with mineral oil. It was then submitted to local overheating, with a comparison to cellulose paper aged with mineral oil to provide a benchmark for evaluation. The results indicate that the cellulose paper within solid hybrid insulation is slightly less degraded compared to the cellulose paper of conventional insulation.