Research On Detection System Of Local Magnetic Property On The Surface Of Iron Core

Local magnetic properties on the core surface refer to characteristics about the change of the magnetic flux density and the magnetic field strength signal,which change with time at a position or a local area of the surface of the motor or transformer core. In general, the magnetic properties refer to the performance parameters of the electrical steel sheet material obtained in the IEC standard measurement system. However, when the electrical steel sheet is laminated to the motor or transformer core, its magnetic properties under the actual operating conditions can change, and magnetic characteristics at different positions of the core are also different. Thus, it is necessary to design a special detection system to measure such local magnetic properties. For this purpose, in this paper, a measurement system was designed and developed for the first time in the country which can be used to detect the local magnetic properties of the surface of the iron core. A sensor probe was made and the accuracy of its measurement coils detecting the magnetic field strength and magnetic flux density signals was calibrated. The research lays a foundation for further study on the real-time detection of local magnetic flux density and magnetic field intensity signal and the measurement visualization about loss distribution. Main contents are as follows:First of all, on the basis of discussing the current situation of the research on measurement techniques about magnetic properties of ferromagnetic materials, a hardware platform of detection system of local magnetic property on the surface of iron core was built. The sensor probe as a key part of detection system was designed and built, in which the magnetic flux density signal was detected by two B-probes and the measurement of the magnetic field strength was completed by two H-coils. By utilizing a high-precision winder purchased by the laboratory, the H-coil was winded and a fixture suitable for winding the H-coil was designed.Then, the parameters about H-coil were determined by using the method combining the simulation calculation and experimental test. The solenoid coil designed to determine parameters of H-coil was modeled and its magnetic field was simulated by a three-dimensional finite element method. The experimental circuit about measuring the H-coil parameter was designed and the measurement software program was developed based on a virtual instrument LabVIEW platform. By collecting and analyzing experimental data, the parameters of H-coil, i.e. the product of the number of turns and the area of the H-coil, were obtained.Finally, the calibration of B-probe was accomplished by comparing experimental results method. The software and hardware structure of B-probe calibration system were designed. A simplified model of a single phase transformer was built and the magnetic flux density signals on the local areas of the model were measured. The average magnetic flux density value at 10 sampling points measured by using B-probe method and that measured by applying traditional winding method were compared and analyzed, and then the measurement accuracy of the B-probe along two detecting directions was calibrated.