Research and Identification of DC Magnetic Bias of Single-Phase Transformer

Abstract

In recent years, the phenomenon of DC bias of transformer in the AC power grid has occurred from time to time. DC bias is an abnormal working state of transformer. It is of great significance to study the DC bias characteristics of transformer. Based on PSCAD software, this paper studies the single-phase transformer that is easily affected by DC bias. Through the establishment of a single-phase dual-winding transformer simulation model, the influence of DC bias on the transformer is studied, including the change of excitation current, magnetization curve of iron core, each harmonic and total harmonic distortion rate under different DC bias conditions. Finally, based on the Discrete Wavelet Transform (DWT), the identification of the low-frequency components in the excitation current is studied, which can be used as an effective judgment for the DC bias fault of the transformer according to the characteristics of the low-frequency components, and the expected effect is achieved.