现有的直流融冰装置存在体积大、重量重、运输困难的问题, 整流变压器是直流融冰装置的核心部件, 优化其结构有利于减轻装置重量, 提升运输便捷性。该文基于变压器基本理论, 提出一种应用于整流变压器的三相立体对称铁芯结构及其叠片方式, 推导电磁场方程和主、互磁通相量关系。随后建立有限元数值计算模型, 分析磁场时变规律及损耗密度分布特性, 提出现有数值计算方法在磁畴微观作用处理上的局限及竖直对称面附加损耗。试制一台容量为4 MV·A的样机并进行热循环空载试验, 结果表明, 样机铁芯损耗是计算值的2.18倍, 各相铁芯竖直对称面附近出现明显温升, 验证了提出的附加损耗。基于此, 给出一种适用于三相立体对称铁芯损耗的校正算法; 最后通过不同容量的4台样机进行试验, 获得算法待定系数。该研究可为三相立体对称铁芯的工程应用提供理论参考。

Objective: With the continuous development of power grids, overhead transmission lines inevitably pass through regions with complex terrain and climatic conditions. In extremely cold environments, ice accumulation occurs on these lines. Under wind loads, the accumulated ice layers vibrate and detach, potentially causing accidents such as broken lines and tower collapses. The DC deicers serve as the primary equipment for power networks to defend against freezing disasters. They utilize Joule heating to raise line temperatures and melt ice and snow. However, existing DC deicers suffer from large size, heavy weight, and difficult transportation. As a core component of DC deicers, the rectifier transformer accounts for more than 70% of the total weight. To improve the mobility of these devices, it is necessary to optimize the structure of the rectifier transformer and reduce its weight. Methods: Based on the transformer theory, a three-phase three-dimensional (3D) symmetric core and its lamination method for rectifier transformers are proposed. The electromagnetic field equations and the phasor relations of main and mutual fluxes were derived according to Ampere's law. A finite element model of a 4 MV·A rectifier transformer was established in Ansys Electronics Desktop. The time-varying law of the magnetic field and the characteristics of the loss density distribution were analyzed. The limitations of existing numerical calculation methods in dealing with the microscopic behavior of magnetic domains and the additional loss in the vertical symmetry plane were analyzed. To verify the analysis results, a 4 MV·A prototype was fabricated and tested under thermal cycling and no-load conditions. Finally, an additional loss shape function expression with the average flux density gradient as the independent variable was proposed. The undetermined coefficients and loss correction formula were obtained by collecting no-load test data of samples with different capacities. Results: The mutual fluxes of the three-phase 3D symmetric core were separated by the vertical symmetry plane of each phase. The core flux density was $\sqrt{3}$/2 of the mutual flux density at any instant. The no-load loss of the 4 MV·A rectifier transformer (calculated using the finite element method) was 4.46 kW, with a maximum value of 1.2×10⁴ W/m³. The loss inside the core was substantially higher than that outside. Considering the microscopic motion of magnetic domains, there theoretically existed an additional loss near the vertical symmetry plane that could not be elucidated by existing algorithms. In the no-load and thermal cycling tests, the measured core loss was 9.73 kW, with an error of 118.16% compared with the calculated value. An obvious temperature rise was observed near the vertical symmetry plane of each phase core, verifying the existence of the proposed additional loss. Three-phase 3D symmetric core transformers with different capacities had similar shape functions, and the coefficients of the proposed correction model were approximately linear with the capacity. Conclusions: By analyzing the electromagnetic characteristics of the proposed three-phase 3D symmetric core, its core loss characteristics and a correction formula were obtained. This study can provide theoretical support for the engineering application of 3D symmetric core rectifier transformers and thereby contribute to the lightweight design of DC deicers. This, in turn, can improve the transportation capability of DC deicers and ensure the winter safety of power grids.