# Energy Harvesting Methods for Transmission Lines: A Comprehensive Review  
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Correspondence: [EMAIL_ADDRESS]; Tel. : +34-937398365  
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Electrical Engineering Department, Universitat Politecnica de Catalunya, 08222 Terrassa, Spain  
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WSN's limited lifetime challenge. However, different challenges related to the stochastic nature of the incoming energy [9] and the influence of environmental conditions have to be addressed to ensure the optimal performance of WSNs [10]. WSNs can be connected, forming a wireless sensor network comprising a network of numerous WSNs using a multi-hop communication arrangement that allows the expansion of the coverage area compared to a single WS while requiring very low power for operation [11]. After the digital revolutions due to the introduction of the computer and the Internet, the Internet of Things (IoT) is considered to be the third revolution, offering many potential advantages to smart grids, such as fault detection and prediction or disaster prevention and prediction, which are complex problems that transmission system operators have to deal with. Therefore, IoT technology can potentially improve power transmission stability, availability, and reliability [12]. Electric power lines are the arteries of today's power systems; therefore, their efficiency, reliability, and stability profoundly impact daily life and the national economy. Transmission lines may operate in remote areas, making routine inspections complex and expensive. Environmental factors such as wind, rain, ice, or extreme temperatures affect the operation of transmission lines. Although the rate of failures in transmission systems is lower than in distribution systems, the first tends to affect more customers and generate higher outage costs. Therefore, the use of self-powered IoT sensors for real-time monitoring of transmission lines, as shown in Figure 1[13], has great potential to solve the problems mentioned above [12]. Electrical grid reliability is a major challenge for utility companies, so solutions based on grid monitoring, diagnosis, and control are receiving special attention [14]. In countries with an important growth of renewable energy sources, grid balancing and congestion is an issue [15; 16]. The safe and reliable operation of transmission lines must take into account the thermal rating to ensure that conductors do not exceed the maximum allowable temperature [17]. Today, dynamic line rating (DLR) approaches are gaining popularity because they offer a solution to the congestion problem since they are based on utilizing the maximum capacity of transmission lines. To this end, DLR approaches are based on measuring weather and line variables in order to dynamically determine the maximum allowable line current to ensure that the line operates within safe operation limits [18]. These solutions also warrant an increased return on investment due to more efficient asset utilization [11]. However, due to the geographical spread of power systems, monitoring power lines and assets outside the substation is challenging due to the harsh outdoor weather conditions, the vast distances to be covered, and the power requirements of the required electronic sensing devices [11]. Figure 1: Schematic of wireless monitoring of transmission lines. In general, in indoor applications, there is no urgent need for EH devices due to easy access to a power supply and accessibility of sensor nodes, which reduces maintenance costs, so the need for EH systems is more typical of harsh outdoor applications [19]. Developing EH systems for high-voltage applications remains a big challenge, so most sensor nodes are still battery-powered, being inconvenient due to periodic replacements and unfavorable maintenance-free operations. As a result, many studies are focusing on self-powered wireless sensors [20].