Insulation Monitoring of Oxidative Aged Nonedible Ester Based Dielectric Fluid by Suitable Dissolved Gas Analysis

Insulation is the weakest link of an oil filled power and distribution transformers. Any dilution in the liquid insulation of the transformer adversely affects the overall performance of the transformer. To understand the degree of insulation degradation, dissolved gas analysis (DGA) is carried out for aged sample of nonedible ester oil (NEO) and compared with conventional mineral oil (MO) based transformer oil (TO). An accelerated oxidative ageing study is performed for NEO and MO at three different ageing stages such as 100, 500 and 1000 hours. The rheological and thermal performances of the aged oil sample are monitored through viscosity and thermal conductivity respectively. Molecular alteration and generation of harmful and flammable gasses from NEO and MO are detected through DGA. Using the basic gas ratio diagnostic technique as per IEC 60599, the probable insulation failures are detected. From the comparative analysis of DGA for NEO and MO, it is observed that marginal insulation degradation occurs for NEO. Due to high thermal conductivity of NEO flammable gas generation is moderated even at severe oxidative environment. Since environment-friendly biodegradable ester oil is more focused recently for transformer application, NEO is likely to be a potential alternative with enhanced insulation integrity with ageing.