Research On Heat Transfer Performance Of Large Oil Immersed Natural Ester Oil Transformer

Mineral oil is by far the most commonly used heat dissipation medium in large oil-immersed transformers.Mineral oil has excellent insulation properties,high stability and low cost,but it has a long degradation time and poor environmental performance.In order to make transformers more environmentally friendly,it has become a trend to use natural ester oil instead of traditional mineral oil as the heat dissipation medium for large transformers.Natural ester oil has a short natural degradation duration and a high biodegradation rate,making it an ideal alternative to mineral oil.Natural ester oil transformers have a longer service life and greater load capacity than mineral oil transformers.However,natural ester oil is highly viscous,and direct replacement of mineral oil with natural ester oil may seriously affect the cooling effect of the transformer.In order to replace the traditional mineral oil with the more environmentally friendly natural ester oil in engineering,it is crucial to conduct research on the heat dissipation performance of large natural ester oil transformers.In this paper,a large oil-immersed transformer non-inductive winding temperature rise platform and a large oil-immersed transformer model SWZ22-50MVA/110 k V were used as research objects.The temperature field simulation calculation model of the winding temperature rise experimental platform and the temperature field calculation model of the large oil-immersed transformer were established and experimentally verified using the finite element method.The heat transfer performance of natural ester oil and mineral oil in forced oil circulation and natural circulation mode was compared and studied.The main work of this paper is as follows:A two-dimensional axisymmetric leakage field model for large oil-immersed transformers was established,and the density distribution of eddy current losses in the transformer was calculated to provide an accurate heat source for subsequent temperature field calculations.A two-dimensional axisymmetric fluid-temperature field calculation model for the forced oil circulation mode of the winding temperature rise testbed was validated.The experimental results show that the maximum error of the model was verified to be less than 3%.A two-dimensional axisymmetric fluid-temperature field calculation model was established for the natural circulation mode of the winding temperature rise test rig,and the maximum error of the model was verified to be less than2%.By defining the concept of "oil temperature advantage difference" and combining the copper-oil temperature difference,the heat transfer model was used to compare the heat transfer performance of natural ester oil and mineral oil in the forced oil circulation mode.The results show that the heat transfer performance of natural ester oil is better than that of mineral oil in the forced oil circulation mode,and the heat transfer performance of natural ester oil is weaker than that of mineral oil in the natural circulation mode.A two-dimensional axisymmetric fluid-temperature field calculation model for large oil-immersed transformers in natural circulation mode was established,and the heat transfer performance of natural ester oil and mineral oil was compared and analyzed by combining the copper-oil temperature difference with the hot spot temperature of each guiding partition.The results show that the heat transfer performance of natural ester oil transformers is weaker than that of mineral oil transformers in natural circulation mode.For large natural ester oil-immersed transformers,the factors affecting the internal heat transfer performance of the transformer were investigated from the viewpoint of axial oil channel size and spoke oil channel size,and structural optimization solutions were proposed.The results show that the heat transfer performance of large natural ester oil-immersed transformers can be optimized by appropriately increasing the axial oil passage size and appropriately reducing the spoke oil passage size.