Cailiao gongcheng (Oct 2023)
Microstructure, magnetic properties and application of 0.20 mm heatproof grain-oriented silicon steel
Abstract
Heatproof low-loss grain-oriented silicon steel is an ideal material for the manufacture of ultra-high energy efficiency (UHEE) transformer with three-dimensional wound-core. The microstructure and grain orientation characteristics of 0.20 mm heatproof laser-scribed grain-oriented (LSGO) silicon steel and mechanically notched grain-oriented (MNGO) silicon steel were studied by optical microscope (OM), scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) techniques. The magnetic properties of two heatproof GO steels after stress relief annealing under sinusoidal and complex conditions were investigated by using an arbitrary waveform magnetic field excitation measurement system. Based on MagNet finite element software, the modeling of 10 kV/400 kVA UHEE transformer core and winding was carried out. Results show that, the mechanism of domain refinement of heatproof MNGO and MNGO steel is completely different. The former depends on the formation of parallel grooves filled by metal oxides on the surface of the original large size Goss grains, and the latter forms randomly oriented grains with a diameter of 40-50 μm in equidistant distribution on the surface of the matrix. The large angle grain boundary and sub-grain boundary can refine the domain and reduce the core loss. During annealing at 850 ℃ for 0-8 h, the core losses of two heatproof GO steel samples decrease first, then increase slightly or tend to be stable, and the loss changes under harmonic and DC-bias conditions are basically the same. The optimization of iron core section, magnetic field and loss simulation are completed. Finally, a 10 kV/400 kVA UHEE transformer with three-dimensional wound-core is successfully developed based on domestic heatproof LSGO steel. Its no-load loss and load loss are further reduced by 17.3% and 7.9% compared with the limit value of energy efficiency level 1 presented in the national standard of GB 20052—2020.
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