Improved Transformer Models Involved with Compensating Current Source for Transient Analysis

When a transformer undergoes transient processes such as overvoltage or closing, it experiences varying degrees of saturation, and the excitation current at the port can even increase to several times the rated current. The current power system simulation software usually expresses the nonlinear characteristics of transformers by setting a compensating current source in the T-type equivalent circuit of the transformer. The integration process and placement position of the compensation current source affect the simulation accuracy of transformer port inrush current. This paper improved the port flux calculation method when the compensating current source is placed on the excitation branch, primary side, or secondary side respectively. Moreover, numerical calculation expression of the port current and the magnetic linkage integral expression of the compensating current source are obtained. Then, $\mathrm{C}++$ language is used to establish numerical calculation programs for different compensation methods. Finally, by comparing the transient inrush currents obtained by different compensation methods with the simulation results of PSCAD, the impact of different compensation methods on the calculation of inrush currents is demonstrated, and the improvement methods of flux integration under different compensation methods are analyzed. The analysis and improvement of compensation methods proposed in this paper can provide a theoretical basis for improving the accuracy of transient analysis.