Residual Flux Measurement of Power Transformer Based on Transient Current Difference
Shipu Wu, Yuzhan Ren, Youhua Wang, Cailing Huo, Chengcheng Liu
Abstract
Power transformer is the main part of the power grid. After some tests and operations of transformers, a certain residual flux density ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$B_{r}$ </tex-math></inline-formula> ) is left in the iron core due to the ferromagnetic material hysteresis phenomenon. When the transformer is switched on with no load, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$B_{r}$ </tex-math></inline-formula> will lead to inrush current. Therefore, research on measuring <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$B_{r}$ </tex-math></inline-formula> is of great significance for transformer protection. In this article, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$B_{r}$ </tex-math></inline-formula> measurement method based on applied dc voltage is proposed. First, combined with the magnetic circuit and transient circuit analysis, the relationship between <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$B_{r}$ </tex-math></inline-formula> and the extremum value of the transient current difference is obtained. Then, the finite element method (FEM) is used to calculate the transient current under different <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$B_{r}$ </tex-math></inline-formula> and test circuit parameters; the suitable test circuit parameters will be determined, and then the empirical formula for calculating <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$B_{r}$ </tex-math></inline-formula> is obtained. Finally, the experimental results verify the correctness of the simulation analysis.