Strategic assets, such as electricity transmission grids, must be operated in a safe, predictable and reliable way. To do so, best practices in the operation and maintenance of transmission networks must evolve to respond to the changing context of pressured grid operators: operation and maintenance standards, laws and regulations, increasing loads, commercial exchanges, etc. This article presents a review of robotic technologies for the effective implementation, assessment and maintenance of overhead power lines.
Currently, live-line work is of paramount importance for most maintenance operations, and the need to maintain system availability is a key factor in the introduction of robotics in this field. In order to maintain or increase the reliability of ageing overhead transmission lines (OHTLs), new maintenance techniques are becoming available to assess and diagnose the condition of various OHTL components. Line inspection and maintenance already benefit from developments in mobile robotics, which can reduce the potential risk to maintenance crews (including live work), reach hardly accessible spans (such as river crossings), perform tedious tasks faster, and decrease costs.
State-of-the-art of robotic technologies
Although some robotic technologies aimed at the assessment and maintenance of OHTLs were developed in the 1990s, most of them were developed after 2000. This article will define and classify robots and robotic technologies with regard to Cigre’s working group (WG) B2.S2’s terms of reference which are to review the existing and developing robotic technologies for effective implementation, assessment and maintenance of OHTLs in order to assist overhead line engineers to improve line reliability and restoring integrity, and to aid asset managers in investing in further development and implementation of these technologies.
Of course, many definitions and classifications of robots and robotics technologies already exist. Agreement on these definitions and classifications within the robotics community has not yet reached a consensus. In an effort to clarify important ideas that will establish a baseline of further discussions, this section aims at specifying reference terminologies relevant to robotics related to the assessment and maintenance of OHTLs.
Transmission line robotics
Four robot classifications are identified here:
Line-suspended robots are designed to serve as the extended eyes and arms of the transmission lineman. Their basic design function is to perform visual inspection in transmission lines which cross difficult right of ways, such as large rivers or mountainous areas. Also, they may perform a condition assessment of steel core wires of aged ACSR conductors, detect and locate broken wires, measure the remaining cross-section of steel wires as well as temporary repair of components. Such robots or moving platforms are able to travel over the live or ground conductor of transmission lines and many of them are able to pass through or cross over different obstacles (Fig. 1).
Unmanned aerial vehicles
Routine inspections and asset condition assessment in many cases are usually carried out using helicopters with trained personnel to capture information for an intended purpose. Currently, electric power utilities are interested in investigating the technology of unmanned aerial vehicles (UAVs) as they give clear images and unique inspection views when they fly close to the transmission lines (Fig. 2).
Robots of this type have achieved autonomous operation as they have been able to verify their own position as they fly and wirelessly transmit images to operators on the ground. Development of this type of robot is very active as more and more prototypes are being built and more players are expected to enter the market as service providers of technology users.
Ground-based robots are designed to remotely capture and control energised conductors and execute tasks which are far beyond human capability from a mechanical and electrical stress perspective. They represent a mature technology, which has been used for more than 15 years, and could be used for transmission structure repair and replacement, insulator replacement, etc. Much of the development has focussed around robotic arms for the manipulation and control of energised conductors.
Other types of robots
In spite of the recent developments in robots for inspection and maintenance of OHTLs, there are still some components which remain mostly off-limits to robots. Towers, insulators and jumper lines are some of the key components of the OHTL infrastructure that may require the use of specialised robots for inspection and maintenance, when not easily accessible from ground-based or UAV systems. Therefore, other types of robots have been developed for less-conventional work, such as tower/pole climbing, insulator inspection and insulator cleaning.
Effective implementation of robotic technologies
Ensuring personnel safety when performing maintenance, inspections and/or upgrades on energised transmission lines is the most important concern and can be significantly enhanced by the use of robots. Further benefits of using robots becomes apparent for access to difficult-to-reach places, and potential time savings which could be achieved. Robotic technologies have already proven to be a valuable means of inspecting certain systems, and robotic inspection is now considered to be a realistic approach for grid owners. A few major utilities have already introduced robots into their maintenance practices, and several are funding projects to do so.
Safety, efficiency, reliability and availability of equipment are the main factors driving this trend. Maintenance tasks, including inspection and repairs, are identified as high-value applications in transmission live-line work. The ability to perform maintenance and inspection services and upgrading transmission lines without shutting down (de-energising) the transmission line has many economic, social and environmental benefits to the network owner.
Future applications of robotic technologies
The future of robotic technologies applied to OHTLs is very promising. There is a wide range of potential future applications of robotic technologies which are limited only by the needs of the industry and imagination. Such applications could include autonomous UAVs for inspection of OHTLs or a UAV to measure compression connector condition. Robotic technologies have the potential to revolutionise the way the power transmission system is constructed and maintained. The opportunity is vast and undiscovered. However, a large number of gaps exist ranging from financial to technical to regulatory. It remains important to continue to have a vision for the future and make steady progress in attempting to reach it.
Inspection and maintenance activities are conducted to prevent degradation of an OHTL asset beyond a desired performance level. The time to perform these required maintenance activities in order to achieve a desired performance level of the OHTL is a critical question. Although failure of an OHTL is not desirable, total elimination of this risk may not be economically justifiable. A transmission line is regularly inspected in order to achieve updated information about the condition of the line as well as the immediate surroundings. Various inspection techniques have been developed to enable the condition of the OHTL to be assessed.
Condition assessment will enable transmission line asset owners to achieve greater efficiency when planning OHTL refurbishments or more effectively to direct their maintenance activities, at a time when systems are ageing and consents for new lines are becoming increasingly difficult to obtain. The inspection should be performed so that the transmission line owner is provided with sufficient information to plan the maintenance of the OHTL. Personnel safety has always been of biggest concern and the practice of energised line work especially in places difficult to reach or when time is critical means the use of robots to assist with maintenance, inspections and/or upgrades on transmission lines can offer a major advantage.
As robotic technologies presently under development become more mature and accepted by utilities as routine tools, applications will emerge requiring the development of new technologies. The key drivers in the emergence of these new robotic technologies will continue to be improved safety, increased reliability, better availability and reduced costs.
This article was first published in the August 2018 issue of Electra and is republished here with permission.
Contact Prince Moyo, Cigre, Tel 011 800-4659, firstname.lastname@example.org
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