Contactless HVDC Overhead-Line Current Monitoring by a Magnetic Sensor Array With Sensing Parameter Correction Function

To improve the efficiency of power transmission, high-voltage direct current (HVdc) transmission systems are crucial power-related development in many countries. This study proposes a contactless dc current measurement method suitable for on-site measurements of HVdc overhead lines. In this method, a vertical magnetic field (MF) sensor array (three layers and one three-axis MF sensor installed in each layer) is designed to measure the spatial MFs on the ground. With the spatial MFs measured by the sensor array and the overhead-line specifications obtained from utilities, the core current algorithm of the proposed method can accurately calculate the current values. In addition, we design a magnetic shielding mechanism to correct a dc offset that is inevitably output from each MF sensor. The dc offset includes the quiescent voltage of the self-circuit of the MF sensor and the output voltage of the MF sensor caused by the earth's MF. Thus, this mechanism can effectively solve the problem in which the dc offset is misjudged as an MF formed by the measured current. The simulation results indicate that under arbitrary vertical sensor array placements, the core convergence condition (geomagnetic invariance) of the proposed current algorithm can improve the algorithm convergence. Finally, the experimental results verify the feasibility of the proposed method for the measurement of overhead-line current. Without conductor sags, all the current errors are less than 2% in both the 500- and 800-kV overhead-line scenarios. Moreover, even with serious conductor sags, all the current errors are still within 9%.