Comparative analysis of the impact of dissolved decay products on the dielectric performances of natural monoesters and mineral oil for power transformers

The challenge of bio-based insulating oil research is the development of a new alternative insulating liquid to mineral oil (MO) for power transformers with identical and even better characteristics in the long run. Under operating conditions, the concentration of dissolved decay contents in oil increases with time and could alter its dielectric properties. This paper presents an experimental study comparing the long-term dielectric properties between castor oil methyl ester (COME), palm kernel oil methyl ester (PKOME) and MO. Six samples of each insulating liquid were submitted to accelerated thermal ageing at 115°C for 432 hours according to ASTM D1934. Every 72 hours, a sample of each insulating liquid is collected from the laboratory oven. Then the breakdown voltage (BDV), the partial discharge inception voltage (PDIV) and dissolved decay products (DDP) of these samples are measured and analysed. The BDV was investigated according to IEC 60156. The PDIV experiment was performed in conformity with a protocol modified from IEC 61294 at ambient temperature. The DDP were evaluated according to ASTM D6802. The experimental findings show natural monoesters have better long-term dielectric performance compared to MO