Washington, D.C., January 12, 2011 — Overhead transmission lines are among the utility industry’s most widely distributed assets, traversing tens of thousands of miles, often in remote locations.
Reliability requirements, component aging, clearance and right-of-way inspection compliance drive the need for thorough, timely inspections along the entire length of these lines.
Such comprehensive assessments by maintenance personnel, working on the ground or in aircraft, currently entail significant expense.
To expand inspection capabilities and increase cost-effectiveness, the Electric Power Research Institute is developing a transmission line inspection robot that can be permanently installed on these lines, and traverse 80 miles of line at least twice a year, collecting high-fidelity information that utilities can act on in real time.
As the robot crawls along the transmission line, it uses various inspection technologies to identify high-risk vegetation and right-of-way encroachment, and to assess component conditions.
After an initial concept design, the EPRI research team refined the design and developed a prototype robot. Nicknamed “Ti,” EPRI has put the prototype through a series of tests at its laboratory in Lenox, Massachusetts and is compiling data that will lead to further refinement of the design.
The Robot in Action – Video Links
Videos have been created to show Ti as it has gone through testing at the EPRI lab. You can follow these links to the EPRI YouTube page where these videos are posted.
Development of a Transmission Line Inspecting Robot; January 2011; 4:57 running time.
Initial Concept Video of Transmission Line Robot Project; 5:42 running time.
Features and Functionality
Ti uses high-definition visual and infra-red spectrum cameras with advanced image processing to inspect the right-of-way and component conditions. It will be able to determine clearances between conductors, trees, and other objects in the right-of-way.
The cameras also will be able to compare current and past images of specific components to identify high-risk conditions or degradation. As an alternative to the camera, the robot may be equipped with a Light Detection and Ranging (LiDAR) sensor to measure conductor position, vegetation, and nearby structures.
Ti will transmit key information to utility personnel, with a global positioning system accurately identifying its location and speed. Another system will collect data from remote sensors deployed along the line, and an electromagnetic interference detector will identify the location of discharge activity, i.e. corona, or arcing. Where discharges are identified, field personnel may do further inspections using daytime discharge cameras.
The conductor-crawling robot has been designed to work with a variety of EPRI-developed radio-frequency sensors that can be placed along transmission lines to provide real-time assessment of components such as insulators, conductors, and compression connectors.
These sensors will likely be deployed in areas of environmental stress or where specific component types have been installed. For example, lightning sensors will be installed in high-lightning areas, vibration sensors will be used in high-wind areas, and leakage-current sensors will be deployed in coastal areas to detect salt contamination.
The deployed sensors will collect data continuously, develop histograms, and determine maximum values. Data will be transmitted to Ti when it is in close proximity and will then be transmitted to maintenance personnel.
The inspection robots, when coupled with these sensors, will be able to provide comprehensive, accurate, and useful information to optimize line maintenance and improve transmission reliability.
In some cases, the purchase of robots for use in place of maintenance crews could shift O&M expenses to capital costs, allowing a return on investment and depreciation.
The transmission line robot will be permanently installed on a transmission line shield wire. It traverses structures and obstacles, e.g. marker balls, utilizing bypass systems that are permanently installed on the transmission line.
The robot automatically disconnects itself from the shield wire and connects itself to the bypass system. Once it is has bypassed the obstacle or structure it then returns to the shield wire.
These bypass systems could be installed during construction or be made integral to the line hardware. It is envisioned that the robot’s mobility could be developed to remove the need for by-pass systems, enabling its deployment on existing transmission lines.
Although Ti may be permanently installed on long transmission lines it can be relocated if required to other transmission lines or it may move from one line to another utilizing a bridge that is installed on nearby structures.
The current version of the robot is designed to inspect an average of 12 765 kV structures and spans per day. It is capable of moving up to five miles per hour if it needs to reach a portion of the line more quickly, for example to inspect a line outage. The robot draws energy through power harvesting and stores it in onboard batteries.
Stages of Transmission Line Robot Development
This research, development and demonstration project began in 2008 and is targeted to result in a field implementation in 2014.
Concept – Initial requirements for the robot developed based on industry knowledge and feedback from utilities. The bypass system, solar panels, sensor package and power requirements were a key emphasis in the concept development design.
Design – A detailed design was performed of both the robot and the bypass systems. Details of mobility as well as the integrated sensor, control and communications package were developed.
Technology Demonstration – Technology demonstrators of both the bypass systems and the mechanical components of the robot were constructed, tested and refined. Testing was performed on indoor short sections of line with bypass systems installed.
Full Scale Laboratory Testing – A test loop was developed where all the challenges that the technology demonstration robot would encounter on a typical 765kV line were simulated (angles and inclination). Bypass systems were developed for each of the challenges, and then refined and installed. The robot was then tested and evaluated as it faced each of the challenges.
Remote RF Sensor – A suite of RF integrated sensors has been developed to continually assess the condition of components and transmit to Ti when it is in close proximity. Leakage current, conductor temperature, vibration, lightning and fault sensors have been developed and are currently being demonstrated at 12 sites.
Bypass System – The Heart of the Technology
One challenge in developing the robot was to create a design that would enable it to move along the shield wire of transmission lines and move past a structure or other obstacles in its inspection path. Ti utilizes bypass systems that are permanently installed on the structure and around objects.
EPRI is testing six systems that will use an additional short section of shield wire by which the robot can bypass the tower structure and other obstacles with no operator input as it makes its way to the next line section. These may be in addition to the normal line hardware or built into the normal line hardware.
For new transmission lines the cost of the additional or modified hardware is negligible compared to the overall cost of the transmission line.
Next Steps in Development
Development of the remote sensors, LiDAR, image recognition and other sensors continues. These sensing systems will continue to be tested and evaluated on utility test sites.
The control and sensing system architecture is being implemented and will be tested in 2011.
EPRI is working with American Electric Power engineers to include the robot and bypass systems in its 765kV transmission line to be built in 2014.