Analysis of Magnetic Performance and Magnetostrictive Properties of Grain-Oriented Electrical Steels under DC Bias Condition

DC-biased magnetization, which is evoked by high voltage direct current (HVDC) transmission, can cause core saturation, vibration acceleration, and temperature rise in DC converter transformer as well as AC transformer with the invasion of DC current into the neutral point. The grain-oriented (GO) electrical steel is the key material for large power transformer, and its magnetic performance and magnetostrictive properties under DC bias condition directly affect the safety margin, energy saving, and noise level of transformer core. In this paper, the effects of thickness, permeability, and tensile stress on the magnetic / magnetostrictive properties of 0.23-mm, 0.27-mm and 0.30-mm series high-grade GO electrical steels under the condition of AC / DC hybrid excitation are researched. Results show that, large thickness, relatively low permeability, and 3 MPa tensile stress can lead to strong resistance against DC bias for the GO steels with the same core losses under sinusoidal excitation. That means the core loss, excitation current, and magnetostriction coefficient can be effectively decreased under DC bias by rational selection of transformer core materials. It`s an alternatively new way to improve the ability of large power transformers to resist DC bias.