Vectorial Magnetic Properties Measurement of Electrical Steel under Triaxial Stress and Different Temperature Conditions

Electromagnetic devices, such as electrical machines and transformers, play crucial roles in electrical energy conversion and transmission. As the focus on global warming and carbon emissions grows, reducing their losses and improving efficiency has become a top priority. However, designing high-efficiency machines and transformers still poses many challenges, including accurately measuring and characterizing the magnetic properties of iron core materials, especially taking into account the effect of rotational magnetization, complex stress, and temperature rise. This paper presents novel systems for magnetic measurement aimed at experimentally investigating the two-dimensional magnetic properties of electrical steel under complex stress and high-temperature conditions. Firstly, an RSST based on a cross-shaped specimen is developed. Mutually orthogonal U-shaped yokes with excitation windings are employed to magnetize the specimen with a uniform magnetic field in the measurement area. The magnetic flux density and magnetic field strength are measured using B- and H-coils, respectively. A calibration method is proposed to address the challenge of accurately determining the cross-sectional area of the B-coils. Integrated B and H sensors are proposed to shorten the leads of the B- and H-coils and reduce the environmental noise. Secondly, a dual-feedback waveform controller has been developed to tackle the challenges posed by the nonlinear characteristics of the measuring system, which enhances the convergence speed and stability of the waveform control. An interactive interface for the measurement system has also been created to facilitate measurements. Comparison tests conducted between different laboratories validate the effectiveness and accuracy of the proposed measurement system. Then, A method for measuring the two-dimensional magnetic properties of electrical steel sheets under triaxial stress conditions is proposed. Three stress-loading systems with compact size, zero magnetic field interference, and low cost are installed in three perpendicular directions. A novel square-shaped vector B-coil is designed to overcome the deformation of B-coils caused by stress. An array of six H-coils measured the tangential components of H near the specimen's surface, revealing that tangential H decreases or increases linearly with distance. Therefore, an array of three vector H-coils and a linear fitting method are proposed, allowing the H-coils to keep a distance away from the specimen and prevent damage to the H-coils from stresses. Measurements are conducted on non-oriented electrical steel under triaxial stress (RD and TD: -20 MPa to 20 MPa, ND: -4 MPa to 0 MPa) and frequencies ranging from 5 Hz to 200 Hz, revealing that tensile stress in the RD–TD plane decreases the loss in the stress direction while increasing the loss in the perpendicular directions; however, compressive stress has a contrasting effect. Finally, a method for measuring the 2 D magnetic properties of electrical steel that considers temperature effects is developed. To ensure uniform heating and prevent specimen deformation, two heating sheets connected to a controller are positioned symmetrically on either side of the specimen. A vector H-coil featuring a ceramic frame has been engineered to minimize the impact of thermal expansion on the cross-sectional area, enhancing the accuracy of measurements. Additionally, the integrated B and H sensor design is optimized with air-cooling channels to enhance heat dissipation and prevent signal amplifier drift due to temperature rise. Based on these improvements, an RSST system capable of measuring two-dimensional magnetic properties across a temperature range from room temperature to 200 ℃ is constructed. The results demonstrate that higher magnetic fields are required to achieve the same flux density as temperature increases. Furthermore, the losses in the NO material exhibit an initial increase followed by a decrease with increasing temperature. This study systematically measured the two-dimensional magnetic properties of core materials under complex stress and thermal conditions, providing insights into the influence of stress and temperature on magnetic behavior and losses. The findings offer critical technical support for the design and optimization of high-performance motors and transformers.