Power transmission line inspection robots: A review, trends and challenges for future research

•Power transmission line inspection robots (PTLIRs) can replace the manual methods.•This paper reviewed the latest PTLIRs developed within the years 2008 to 2019.•Obstacle avoidance has been challenging and tasking for the climbing robots.•Hybridizing the flying and climbing robots shows an excellent inspection approach.•Limited battery capacity and electromagnetic interference affects the PTLIRs. Routine inspection of a power transmission line (PTL) system for early fault detection and maintenance is crucial for efficient transmission of electric power to consumers. Unlike the conventional manual inspection methods that are labor intensive, dangerous and expensive, an efficient inspection using robots has been a key research interest for many research institutes around the world. This paper presents a comprehensive review and trends of power transmission line inspection robots (PTLIRs) focusing on the latest research achievements within the years 2008 to 2019. The structure, operation, and limitations of the inspection robots, namely, climbing, flying, and hybrid (climbing-flying) robots are extensively discussed. Although climbing robots provides the most reliable inspection data due to their proximity to the line, landing the robot on the line as well as obstacle avoidance has been challenging. Thus, hybridizing the climbing and the flying robots have proved to be an excellent approach to the robotic PTL inspection. Furthermore, power supply, automatic obstacle detection, and control system which are the main challenges of PTL inspection are presented. Finally, it is has been concluded that challenges such as limited on-board battery capacity, unreliable line fault detection, electromagnetic shielding, de-icing mechanism and advanced control techniques for external wind disturbance would be a promising future research direction for researchers in the field of robotic PTL inspection.