电力变压器铁心的非线性磁化特性

Iron Core Nonlinearities of Power Transformer

电磁暂态仿真是电气设备设计、绝缘等级研究和继电保护的基础。在计算机上进行这些研究,需要提供各种元件的仿真数字模型。变压器及其相关模型的建立对励磁涌流、磁滞、谐波和分次谐波的研究尤其重要,且变压器铁心的非线性特性又是变压器建模的关键。为此,从考虑铁心损耗的空载单相变压器模型出发,根据变压器励磁磁链与磁化电流的关系将基本磁化曲线分段线性化,运用迭代的方法求得每个分段下磁链的最大值。利用分段电压峰值与对应分段的等效电阻的关系,求得了该分段磁链与磁化电流曲线的斜率。根据求得的每个分段磁链的最大值及该线性化分段的斜率,从而较为精确地求得了磁链与磁化电流的关系曲线。分段数N可根据精度的需要选取。该方法充分利用了已知的变压器励磁电压电流关系和空载实验的各种数据,直观简洁,并可以根据需要调节计算精度。仿真验证了该方法的正确性和有效性。

Simulation of electromagnetic transients is the foundation for designing equipment and studying insulation coordination and relay protection.To carry out these studies on digital computers,mathematical models are needed for the various components.Model for transformers is especially important for studying inrush currents,ferroresonance,harmonics and subharmonics,in which iron core nonlinearities play an important role.After reviewing the theory of saturation characteristics of transformers,a new piecewise linearized approach,which takes account of iron core losses and bases on the transformer test data provided by the manufacturer,is presented for the computation of the saturation characteristics iron cores.The basic magnetization curve is piecewise linearized by considering the relationship of the excitation flux and the magnetization current,then the maximum value of each section of the flux is obtained by using iterative methods.The slope of each section of the characteristic of the flux and the magnetization current is obtained by using the relationship of the peak voltage and the corresponding equivalent resistance.Then the relationship of the flux and the magnetization current can be obtained precisely by adopting the peak flux of each section and the slope of the piecewise linearized section.The number（N）of the sections is determined according to the accuracy required.The results of simulation prove that the proposed method is correct and valid.