Residual Flux Density Measurement of the Single-phase Transformer based on the Composite Indictor

Accurate measurement of residual flux density in transformers is essential for ensuring safe, reliable, and efficient operation in power systems, which enables controlled switching strategies, such as point-on-wave energization, minimize inrush current, improve operational reliability, and extend equipment life. This paper presents a procedure for determining the residual magnetic flux density in a single-phase transformer. A three-level DC voltage, with an amplitude substantially lower than the transformer’s nominal voltage, is applied to the winding. Using the finite element method (FEM), the coefficients of an empirical formula describing the relationship between the proposed composite indicator and the residual flux density are derived. The proposed approach requires only voltage and current measurements from the transformer. Simulation results are provided to verify the accuracy and effectiveness of the method.