The converter transformer is used to change AC in one side into DC, mostly applied in an electrical swtichyard or an electrical substation. During its actual operation, the load current contains a large number of high-order harmonic components, resulting in uneven distribution of its internal losses and local overheating in a certain area. Excessive temperature can accelerate the aging of insulation materials, thereby reducing the performance of converter transformers and shortening their lifespan.
In the composition of converter transformers, the losses of windings and local overheating are most significantly affected by harmonic currents. Therefore, harmonic losses must be considered in the thermal design of windings to ensure that the temperature rise of the winding hot spot is lower than the specified temperature rise during the operation of the converter transformer, improve the stability of transformer operation, and extend its service life.
In addition to considering the above non-uniform losses, the winding has the characteristics of complex structure and large difference in component size. Therefore, accurate thermal modeling is crucial for studying the impact of harmonic current on the winding temperature distribution characteristics. The following key issues must be solved in the numerical calculation of winding temperature, specifically: ① the entire winding needs to be modeled and high-quality mesh generation needs to be carried out; ② It is necessary to consider the influence of the internal oil ducts of the winding on the heat transfer of the winding; ③ The impact of insulation paper on the heat dissipation of the winding needs to be considered.
Engineering experts at home and abroad have conducted extensive research on the impact of harmonic current on winding loss and hot spot temperature, but most of the current research focuses on the impact of harmonic current on the loss value and hot spot temperature, and lacks quantitative analysis of the impact of harmonic current on the loss and temperature distribution characteristics. However, it is necessary to study the winding loss and temperature distribution characteristics. On the one hand, it can guide the local strengthening of heat dissipation in the winding thermal design, which is conducive to reducing the hot spot temperature and improving the temperature uniformity; On the other hand, it can provide reference for later troubleshooting, thereby shortening maintenance time, and is of great significance for improving economic benefits and ensuring social electricity stability. And also, a harmonic filter pre-assembled in an electrical switchboard would be a solution as well.
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