Magnetic Field Energy Harvesting Under Overhead Power Lines

Condition monitoring for overhead power lines is critical for power transmission networks to improve their reliability, detect potential problems in the early stage, and ensure the utilization of the transmitting full capacity. Energy harvesting can be an effective solution for autonomous self-powered wireless sensors. In this paper, a novel bow-tie-shaped coil is proposed, which is placed directly under overhead power lines to scavenge the magnetic field energy. Compared to the conventional method by mounting the energy harvester on the power lines, this approach provides more flexibility and space to power bigger sensors such as the weather station. As the harvesting coil cannot entirely enclose the power lines, the demagnetization factor that is closely related to the core geometry should be considered and optimized. Thus a new bow-tie-shape core is designed to produce a much lower demagnetization factor (hence more power) than that of the conventional solenoid. The selection of core material is studied and found that Mn-Zn ferrite is the most suitable core material because it greatly reduces the eddy current losses and also has high permeability. Experiment results show that the bow-tie coil could have a power density of 1.86 μW/cm³ when placed in a magnetic flux density of 7 μT_rms. This value is 15 times greater than the reported results under the same condition. If a longer bow-tie coil with more turns is placed in a magnetic flux density of 11μT_rms, the produced power density is 103.5 μW/cm³, which is comparable to a solar panel working during a cloudy day. Thus, the proposed solution is a very efficient and attractive method for harvesting the magnetic field energy for a range of monitoring applications.

I. Introduction

For electric power transmission networks, high-voltage overhead power lines are of great importance. Due to temperature variations, aging effects, and ice accumulation [1], [2], the sag of the conductor may lead to dangerous circumstances and huge maintenance costs [3]. Hence, monitoring overhead power line conditions, disturbances, faults, and sags is essential to ensure the proper operation of the power line transmission networks. Several critical parameters such as the ambient temperature and the line current may affect the operability and availability of overhead power lines. With the advancement in wireless communication technologies, inexpensive and ultralow power wireless sensors have been developed and can be applied to monitoring these important parameters. However, the finite life span of the batteries which power the sensing system becomes a bottleneck as it is expensive to periodically replace these batteries. Thus, the energy harvesting technology is an attractive and promising solution to make the system monitoring self-sustainable [4].