# A Novel Excitation Approach for Power Transformer Simulation Based on Finite Element Analysis
## 1 Introduction  
Transformer manufacturers design power transformers based on factors such as insulation, efficiency, and cooling systems. In the optimal design of the transformer, it is necessary to consider the technical specifications, material costs, manufacturing costs, and capitalization costs [1, 2]. Therefore, the design of the transformer involves multiphysics coupling and cost functions. It is difficult to find the best solution in limited time. If the operating conditions of the transformer can be predicted faster and accurately, the optimal design can be optimized. In [3], the three-phase five-leg wound power transformer was tested. The local magnetic flux density of the inner and outer corners, yokes, and limbs of the iron core was measured. The results show that the magnetic flux density of the outer corner, yoke, and limb is lower than that of the inner corner, yoke, and limb in the iron core. In [4], the magnetic field distribution of the U-type transformer was simulated based on the finite element method under different air gaps. In [5, 6], the evolutionary algorithms combined with the finite element method were used to optimize the design of transformers. There are genetic algorithms (GA), differential evolution algorithms (DEA), and non-dominated sorting genetic algorithms (NSGA-II). The results showed that the design size of the core magnetic flux density affects the efficiency, total cost, and life cycle in the transformer. In [7], simulation software ANSYS Maxwell and ANSYS Mechanical were used to simulate the total iron loss and temperature of a three-phase five-limb power transformer with a capacity of 325 MVA. The simulation results were used to check the cooling system of the design in the transformer. In [8], the magnetic flux distortion of the three-phase five-limb transformer with direct current was analyzed based on the finite element analysis method. In [9], the magnetic field distribution and temperature distribution of three-phase three-limbed transformers were simulated based on the finite element method under DC bias. In [10], the local magnetic field distribution and eddy current loss with direct current offset were analyzed based on the circuit modeland magnetic circuit model. The results showed that the peak magnetic flux density of the iron core will increase during the half-cycle under the DC bias, which is likely to cause vibration and local overheating of the transformer. In [11; 12; 13; 14], scholars performed model fitting and research on the stray loss of transformers based on the finite element method. In [15], the stray loss of the high-frequency transformer was simulated based on the spectral element method.  
According to the above applications, the magnetic flux density of the iron core in the transformer was studied. However, research on finite element analysis of fitting models is still lacking in the three-phase five-limb transformer. Therefore, this paper uses the software of ANSYS Maxwell to simulate the three-phase five-limb transformer in the time domain. The finite element model considers factors such as the structure of the iron core, the non-linear characteristics of the material, and the external excitation. The simulation results calculate the instantaneous magnetic flux density distribution and total core loss. The prototype of the three-phase five-limb transformer is measured to verify the proposed fitting model. Moreover, this paper studies the method of external excitation, which improves the accuracy of the simulation results. Finally, the proposed finite element analysis model will help transformer manufacturers reduce costs and improve efficiency and reliability in three-phase five-limb transformers.