Performance Analysis of Insulating Liquids for Synthetic Ester Retrofilling Mineral Oil Transformer

With the adoption of synthetic ester based on the benefits of fire safety and environment friendly, more and more mineral oil based transformers have been retrofilled. Based on current retrofilling process, mixture of mineral oil and synthetic ester is inevitable. To evaluate retro filled transformer performance, the physicochemical and dielectric parameters of mixed fluids applied after retrofilling have been studied in this paper. At the same time, the different mixture ratio fluids have been identified as different testing samples from 0% to 5% mass percentage of mineral oil to simulate different scenarios under operation. It was concluded less than 5% of residual mineral oil has negligible impact on the dielectric properties of synthetic ester, both the breakdown voltage and DDF of the synthetic ester all meet the benchmark endorsed by lEC 61099.