Measurement of Transformer DC Bias Current Based on Integrated Array Magnetoresistance Sensors and Signal Fusion Algorithm

Accurately measuring transformer dc bias current is crucial due to its significant impact on the operational stability of the power system. It is difficult for the existing technologies to balance the requirements of high sensitivity, reliability, and convenient installation. This article presents a noncontact dc bias current measurement probe using tunnel magnetoresistance (TMR) sensor arrays. The probe contains 16 sensors, which are divided into four arrays. The sensors are bare die chips diced from an 8-in wafer and then wire bonded on a printed circuit board (PCB). The distance between two adjacent sensors in an array is only 0.5 mm, resulting in approximately uniform magnetic field gradient for the sensors simplifying the calculation of the output. The sensors are connected as a push-pull Wheatstone bridge to convert the change of resistances to a voltage signal and to enhance the sensitivity. The distribution of the magnetic field is calculated numerically and the Shannon entropy of the signals is estimated. Then, the output signals are fused based on the weights calculated according to the magnetic field distribution and the Shannon entropy. This method allows for a balanced integration of both the linear characteristics of the signal and its intrinsic properties. Experimental results demonstrate that the system achieves a relative linearity error less than 0.95% for measuring dc currents in the range from -3000 to 3000 mA. This method is an alternative approach that can be utilized in the power system to monitor the transformer dc bias current.