Research On Steinmetz Loss Model Under DC Bias

When the transformer is running under dc bias,the transformer core will work in the magnetic flux density saturation region,which may increase the core loss,aggravate the vibration and noise of the core,and even destroy the stable operation of transformers.For many years,domestic scholars have been paying attention to how to effectively control the dc bias phenomenon of transformers,while the influence of dc bias on the magnetic properties of transformer core is still a matter of recent years.So an accurate calculation of core loss under dc bias is especially important for improving the operating efficiency of the transformer.Based on the magnetic properties of grain-oriented electrical steel sheets measured by Epstein frame setup in our laboratory,in this thesis,the influences of dc bias on the hysteresis characteristics and loss characteristics of electrical steel sheets are analyzed.Based on the traditional Steinmetz loss formula,this thesis proposes an improved Steinmetz loss model taking the dc bias into account.Finally,the research results above are applied to magnetic performance simulations of power transformers to calculate the core loss of the transformer under dc bias.The main research contents are as follows:Firstly,based on the Epstein frame experiment in our laboratory,the magnetic properties of grain-oriented electrical steel sheets with and without dc bias excitation are measured,and the influence of dc bias on the core loss.Based on a large amount of experimental data,the dc bias magnetic induction B_dc is obtained by a mathematical algorithm.The relationship between the dc bias magnetic induction B_dc and the dc bias magnetic field strength H_dc and the alternating current?ac?magnetic induction B_ac is discussed.Then,based on the measured data,the traditional Steinmetz loss formula is analyzed and studied.An improved Steinmetz loss model by introducing a dc bias magnetic induction B_dc is proposed.At the same time,in order to improve the accuracy of model calculation,a dc bias variable coefficient is employed in this loss model.This introduced variable coefficient is fitted using a surface response model.The improved Steinmetz loss formula under dc bias is compared with the experimental measurements to verify the effectiveness of the model.Finally,the improved Steinmetz loss model under dc bias is applied to the simulation of power transformer core loss.The commercial software MagNet is used to simulate the transformer model,and analyzed the variation of core flux density under dc bias.The improved model calculation results and finite element software simulation ones are presented,which provides a reference for the study of dc bias performance of power transformer.