The Magnetic Circuit Design And Dynamic Characteristic Of FBG-GMM Based On Current Transformer

It is a new attempt for current transformer based on giant magnetostrictive material(GMM) and fiber Bragg grating(FBG). GMM-FBG current transformer with ferromagnetic loop is designed based on the magnetostriction characteristics of GMM by finite element method.Magnetic circuit system without bias magnetic field is optimized by finite element method. The effects of the dimensions of GMM and ferrimagnetism on magnetic field are studied. The dimensions of GMM and ferrimagnetism are obtained according to the uniform and magnitude of the magnetic field. The numerical relation between exciting current and magnetic field in GMM is deduced in the optimized system. The measurement range of current is limited by linearity range of GMM, so an adjustable air gap is set in magnetic circuit. The numerical relationship between the air gap and the measurement range of current is defined. The rationality of the designed structure is qualitatively analysed by 2-D simulation, the relationship between exciting current and magnetic field is accurately calculated by 3-D simulation.Permanent-magnets which are set in magnetic circuit to provide bias magnetic field for GMM are designed by finite element method based without bias magnetic field optimization. The charge magnetism size and cross-section area of permanent-magnets are optimized by finite element method. Permanent-magnets have the same cross-sectional area as silicon sheet, its charge magnetism size is 1.8mm, which can provide 30 kA ? m?1bias magnetic field for GMM. In this system, the static operating point of the sensor is changed by adjusting the charging magnetism dimension of permanent-magnet.The experimental results show that the relationship between exciting current and magnetic field in GMM is accurate in 3-D simulation and setting method of permanent-magnets can provide enough bias magnetic field for GMM.Because the harmonic frequency of GMM free bar is related to its dynamic characteristics, amplitude-frequency characteristics of different structure GMM is analysed with modal theory by ANSYS. The harmonic frequency and frequency bandwidth of the GMM are inversely proportional to its length and have nothing to do with its cross-sectional area. To avoid the resonance of the system in running, GMM bar with 15 mm×3mm×3mm is selected, whose harmonic frequency is 32.4kHz. The strain of GMM does not change with the frequency in the frequency range of 50Hz~1000Hz in exciting magnetic field experiment, which can prove the validity of modal analysis in 1000Hz.