The Influence of Iron Particle Contamination on the Breakdown Characteristics of Circulating Mineral Oil under DC Voltage

The presence of metallic particles can lead to the degradation of transformer oil due to the intensification of the electric fields near the conductive components. The primary objective of this research was to investigate the impact of iron impurities on the electrical properties of Mineral Oil (MO), particularly under conditions of continuous flow. Five distinct samples with varying levels of contaminants were carefully prepared for analysis. A specialized chamber was designed to replicate the circulation conditions of oil within an operating transformer. The focus of the investigation was on the breakdown characteristics under DC voltages. The results indicated that higher concentrations of iron impurities were associated with a reduction in breakdown voltage although the circulation of oil exhibited a beneficial effect. To validate these findings, Finite Element Method (FEM)-based simulations were conducted. The analysis of the electric field distribution revealed that iron impurities amplified the electric field intensity, while circulation served to mitigate this effect. Furthermore, the simulations tracking the trajectory of iron particles demonstrated that circulation hindered the particles from reaching the electrodes, thereby diminishing discharge events and lowering the risk of dielectric failure. In conclusion, the circulation of MO enhanced its breakdown voltage, although the presence of iron contamination could still pose a risk under DC voltage conditions.