Inhomogeneity and Local Distortions of Magnetic Flux in a Single-Phase Transformer Core Package

In transformer cores, path length differences, material anisotropy, magnetic saturation, and impact of the overlaps (OLs) cause regional induction inhomogeneities and distortions. The global building factor of the core shows significant increases. The local distributions of induction and distortion are calculated numerically along the three magnetic flux paths, inner path (IP), middle path (MP), and outer path (OP) in a single-phase transformer core package. For the calculations, the novel magnetic equivalent circuit calculation-method is used. The latter takes the non-linear permeability functions in rolling and in transverse direction as well as non-linear effects of OLs into account. The static local induction distributions were calculated for global induction values B GL up to 1.80 T. For B GL = 0.9, 1.3, and 1.7 T, the resulting local inhomogeneities are discussed. As a second step, the quasidynamic waveforms of B(t) were reconstructed by setting of individual static instantaneous numerical calculations in a sequence. The corresponding distortions of the quasi-dynamic waveforms are evaluated for sinusoidal excitations with B̂ GL = 0.9, 1.3, and 1.7 T. For validations also, regional measurements were performed. The results show complex inhomogeneous induction distributions with variations of up to 5% for 1.7 T, but up to more than 40% for 0.9 T. While the MP-flux tends to be almost sinusoidal, the OP and the IP show high distortions.