Real-time Load Current Monitoring of Overhead Lines Using GMR Sensors

TL;DR

Problem: safe, non-contact, real-time monitoring of currents in overhead distribution lines. Approach: use GMR sensors to measure magnetic fields at distance and compute phase currents via a geometry-driven cross-coupled transformation, with $I = \frac{4\pi}{\mu_0} \mathrm{C_{xz}}^{-1} [\vec{B_x}; \vec{B_z}]$, implemented in a MATLAB dashboard for live visualization. Contributions: practical GMR-based current sensing with calibration, a Biot–Savart–based field-to-current mapping, and experimental validation against Hall-effect references under linear and nonlinear loads, achieving residuals within $\pm 2$ A and NMAE up to $35.36\%$. Significance: enables low-cost, galvanically isolated, real-time overhead-line monitoring with sampling up to $28$ kHz.

Abstract

Non-contact current monitoring has emerged as a prominent research focus owing to its non-intrusive characteristics and low maintenance requirements. However, while they offer high sensitivity, contactless sensors necessitate sophisticated design methodologies and thorough experimental validation. In this study, a Giant Magneto-Resistance (GMR) sensor is employed to monitor the instantaneous currents of a three-phase 400-volt overhead line, and its performance is evaluated against that of a conventional contact-based Hall effect sensor. A mathematical framework is developed to calculate current from the measured magnetic field signals. Furthermore, a MATLAB-based dashboard is implemented to enable real-time visualization of current measurements from both sensors under linear and non-linear load conditions. The GMR current sensor achieved a relative accuracy of 64.64% to 91.49%, with most phases above 80%. Identified improvements over this are possible, indicating that the sensing method has potential as a basis for calculating phase currents.

Figures (6)

• Figure 1: A three-phase isolated delta-wye configured transformer supplies stable power to the load through overhead lines. The Hall-effect and GMR sensors are powered by five and eight-volt regulated DC power supplies. Each GMR sensor output is filtered via a low-pass filter to eliminate the anti-aliasing effect and high-frequency noise. The Hall effect sensors have integrated filter units; therefore, external filters are unnecessary. Both types of sensor data are subsequently sent to the National Instruments Data Acquisition System (NI-DAQ). Finally, the data from the NI-DAQ is processed and plotted using MATLAB application.
• Figure 2: The position of the GMR sensor with respect to the overhead power lines is illustrated. Here, OTn (where n = 1 to 4) denotes the single-axis GMR sensor mounted on a 3D-printed sensor holder.
• Figure 3: Comparative analysis under linear load conditions shows that the measured magnetic field from the GMR sensor closely overlaps with the field calculated using (\ref{['BxBz1']}) (3rd row). The residual field (4th row) represents the instantaneous difference between the measured and calculated values.
• Figure 4: Comparative analysis under non-linear load conditions shows that the measured magnetic field from the GMR sensor closely overlaps with the field calculated using (\ref{['BxBz1']}) (3rd row). The residual field (4th row) represents the instantaneous difference between the measured and calculated values.
• Figure 5: Comparative analysis under linear load conditions shows that the phase current calculated from GMR sensor data using (\ref{['eq:I-back']}) closely matches the measured current signal (3rd row). The residual current remains within $\pm 2\,\mathrm{A}$ (4th row).