Research on Magnetically Balanced High-Current TMR Sensor for EAST Poloidal Field Power Supply

A magnetically balanced tunneling magneto-resistance (TMR) sensor for high-current measurement was developed to meet the measurement requirements of experimental advanced superconducting tokamak poloidal field (EAST PF) power supply. The difficulty in the research of magnetic balance type high-current sensors is in analyzing and predicting their operating parameters under different working conditions. Analyze the compensation coil and iron core and verify the output parameters of secondary winding based on these operating parameters. In order to obtain the operating parameters under different working conditions, the balance equation of magnetic induction intensity and the characteristic matrix of the magnetically balanced sensor based on linear assumption are proposed. The operating parameters are simulated by the 3-D finite element method. Through simulation and experimental tests, the measured current values of the secondary coil are compared with the theoretical values. The comparison results are consistent with the theoretical analysis. The sensor prototype is also tested continuously for 24 h (20 kA current), the compensation coil was not burned out, and the iron core was not saturated. The sensor measurement accuracy was better than 0.4%. The results prove the correctness and practicality of the proposed analysis method. In addition, external magnetic fields and ferromagnetic materials may become sources of external interference, leading to imbalanced operating parameters between secondary windings. If the interference degree is high, it may cause overcurrent and overheating in certain secondary windings.