Study on the Influencing Factors of Hot Spot Temperature of Oil-immersed Distribution Transformer Windings

The integration of distributed power and seasonal load fluctuations worsens three-phase imbalance, raising the risk of transformer winding overheating and possible failure. This paper uses 3D finite element simulation and experimental validation to study the effects of three-phase current imbalance, ambient temperature, insulation thickness, and thermal conductivity on the temperature of hot spot in transformers. It is shown that the hot spot temperature is directly affected by the average copper loss rate and the single-phase maximum current. Ambient temperature has a greater effect on the hot spot temperature of transformers with lower average copper loss rates and with windings with lower load factors. The higher the equivalent thermal conductivity of the windings and the thickness of the thin layer, the higher the hot spot temperature of the transformer, which is more pronounced on transformers and windings with higher average copper loss rates and higher load rates.