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

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.

💡 Research Summary

The paper presents a practical approach for non‑contact, real‑time monitoring of phase currents in a 400 V three‑phase overhead line using off‑the‑shelf Giant Magneto‑Resistance (GMR) sensors. Recognizing the limitations of traditional contact‑type current transducers—Hall‑effect sensors, Rogowski coils, and current transformers—the authors explore GMR technology, which offers high sensitivity, wide bandwidth, galvanic isolation, and low cost, but suffers from magnetic field coupling and sensor placement challenges.

A geometric model is derived based on the Biot–Savart law. Two 2‑D GMR sensor heads are mounted orthogonally to capture the horizontal (Bx) and vertical (Bz) components of the magnetic flux density generated by each conductor. The model introduces spatial coefficients Cx and Cz that depend on the relative positions of the conductors and the sensors. By integrating the contributions of differential current elements along the span, the magnetic field at each sensor is expressed as

 Bx = μ0 I Cx / (4π) , Bz = μ0 I Cz / (4π)

where I is the unknown phase current. For four conductors (A, B, C, N) and two sensor heads, the coefficients are assembled into a 4 × 4 cross‑coupled matrix Cxz. Since the matrix is purely geometric, it remains constant after installation. The measured field vector