Julien Beaudry, Nicolas Pouliot, Matthieu Montfrond, Serge Montambault
Hydro-Québec Research Institute (IREQ), Canada
The means to inspect and maintain such strategic infrastructure as power lines and substations must evolve. For 25 years, Hydro-Québec has been developing robotic platforms, sensors and tools to meet the new challenges associated with operating a power grid: increasing demand for energy, stricter regulation, aging assets, extreme weather events, live-line and in-situ maintenance requirements, etc.
This paper discusses Hydro-Québec’s robotic technologies now applied in operations, achieving missions to gather strategic data and performing live-line maintenance tasks. IREQ’s Powerline Robotics Program has been successful in developing several technologies now deployed worldwide, such as LineScout and LineCore technologies. Recent developments in drones and their payloads, very promising for power line and substation missions, are also discussed. A number of substation robotic projects are presented. The benefits of developing and implementing robotics in maintenance practices are discussed, as substantial economic and strategic benefits have already been reaped.
As an owner and operator of power generating stations, transmission lines, substations and distribution networks, Hydro-Québec must manage responsibly for a diversified fleet of highly valuable strategic assets. For such a company, asset management not only entails highly complex optimization problems but also leverages sophisticated technical means both for gathering detailed asset health status measurements and for supporting crucial maintenance work by dedicated field employees. With aging assets and the need for optimal asset management strategies, proper management is infeasible without the help of recent advances in technology. There has indeed been major progress in many technological areas related to inspection and maintenance by electric utilities. This paper focuses on one recent area, already used in the field with convincing results and promising an even brighter future: robotics.
Hydro-Québec’s research institute, IREQ, has for decades been conducting research on robotics solutions and developing them to help the electric utility carry out its inspection and maintenance activities. This paper overviews the portfolio of robotics systems and expertise that IREQ has built up since its inception. An earlier paper has a more detailed focus on robotics dedicated to power lines . IREQ has substantial expertise in power line robotics, the potential yield of which should appear in substations in the coming years. The focus of the paper then shifts to robotics applied in substations, with a brief review of the state of the art, a presentation of IREQ’s accomplishments in this environment, and a closing overview of new opportunities for robotics in substations, given the advances in such areas as sensing, embedded computing and machine learning.
Hyrdo-Québec’s Robotics Group
The main mission of IREQ is to develop technological solutions to address the company’s specific needs in the generation, transmission and distribution of electricity. IREQ’s Inspection and Maintenance Robotics department focuses on robotic solutions for tackling issues in all areas of the business. It has been doing so for 25 years, developing and demonstrating over this period such diversified innovative systems as:
- Robotic platforms, mainly vehicles and manipulators
- Multiprocess robotic repair systems
- Localization and vision systems
- NDT sensors
- Related algorithms, software and other peripherals
With over 99% of the energy produced by Hydro-Québec coming from hydropower generating stations, the utility owns and manages a total of 62 power dams and over 570 control dams and structures spread across a vast territory. To inspect these assets, IREQ has developed robot systems in the form of underwater remotely operated vehicles (ROVs). These vehicles are used for visual inspections and more sophisticated sensing, like 3D mapping of the underwater floor or automated concrete crack measurements. Several generations of ROVs have been developed , the latest and most advanced being Maski+ (see Figure 1a).
Robotic in-situ repair and construction of large hydropower equipment involves a daunting set of tasks to perform in a challenging environment. Such challenges have been addressed at IREQ with the SCOMPI portable robot. A range of tasks have been successfully field demonstrated with SCOMPI: turbine blade repair and reshaping, refurbishment of head and spillway gates, and welding of penstock sections. A more detailed description of the robot system, shown in Figure 1b, and the main processes it performs (grinding and welding) are given in . While numerous and varied robotic processes have been studied and integrated into SCOMPI, more recent ones have been laboratory tested and possible applications are promising. One example is a new heat treatment technique using a robotic induction process.
Other IREQ inventions addressing underwater structures include WireScan, an automated submersible laser-based high-precision measurement system. The system and its applications for measuring inside hydraulic gate frames are presented in . Robotic solutions addressing specific distribution network problems have also been developed. A good example is the mobile robot system designed to operate circuit switches in underground vaults .
The paragraphs above overview robotic systems developed at IREQ for applications outside of power line and substation environments, which will be covered in the following sections. Features shared by all of these robot systems are their reliability and robustness under challenging operating conditions, including underwater operation, adverse weather during hot summers and cold winters, live-line work at high voltage levels and work in confined spaces.
Power Line Robotics
Overview of the Benefits
Traditionally, power line inspections are performed by line technicians who survey an extended territory in road vehicles, all-terrain vehicles and helicopters or airplanes. These methods enable broad, general inspections suitable for identifying such major defects as broken wires, broken insulators and structural damage to towers. When necessary, line technicians will of course use binoculars, climb towers or even perch on the conductors aboard conductor carts.
The introduction of teleoperated robotic systems at the turn of the century did not dramatically alter or replace these traditional methods. As such systems become available, however, they provided new, complementary approaches that proved their value in a time of aging assets, when systematic collection of quantitative data is required to support information-driven decisions based on utility asset management principles.
More specifically, it has been demonstrated that robotic technologies can be advantageously used in the field of power line inspection and maintenance for the following purposes: • Generating quantitative objective data, which can be archived and compared with datasets collected either at the same location some time ago (evolution) or at other similar locations (comparison)
- Improving work efficiency by optimally splitting tasks between those best performed by humans and those more appropriately carried out by robots
- Contributing to continuity of service by avoiding certain planned outages required to perform human maintenance
- Ensuring power system reliability by pinpointing sensitive areas
- Simplifying the work of line technicians and improving their safety by reaching challenging sites
- Optimizing required refurbishment investments by objectively establishing when a given asset will reach its end of life
In order to maximize their value, robotic systems should be deployed without expensive infrastructure retailoring: they must adapt as much as possible to existing components. Such adaptability is a particularly daunting objective given the age of power grids, where a wide variety of components exist, sometimes poorly documented in the company database.
Line Suspended Vehicles
The adaptability constraint was strictly followed when LineROVer and LineScout were designed at IREQ: these technologies had to mesh with proven working methods and be sufficiently open-ended to suit the range of existing line configurations. While LineROVer is a simple teleoperated trolley, able to roll over splices and provide high traction force (> 600 N), LineScout is a ruggedized moving platform supporting large payloads (> 10 kg) and capable of crossing obstacles up to 760 mm in length.
Both line suspended vehicles were used extensively on energized and de-energized power lines on a number of power utility grids around the world. They have proven their value in gathering useful information in difficult-to-reach locations, such as large river crossings, highway crossings, and risky locations, like lines with conductors damaged to an unknown extent. In addition to several HD cameras that provide incomparable, steady points of view, other application tools were introduced over time, such as a robotic arm, torque wrench and broken-strand repair module. These specialized tools broaden the applicability of these systems, opening the way to performing maintenance tasks from a distance .
Since LineROVer and LineScout were introduced in 2002 and 2006 respectively, they have been the basis of several initiatives launched around the world, as reported in surveys on the state of the art . Around 2012 at IREQ, the constantly updated technology roadmap clearly identified that the development of specific sensors was the most valuable step to undertake next.
Power Line Inspection Sensors
Line suspended vehicles on energized power lines offer the great advantage of being able to collect invaluable data in hard-to-reach locations. Visual signs of external damage, such as “birdcaging” and those left by lightning strikes and gunshots, are important since they affect the mechanical integrity of the conductor. However, the inner condition of conductors is probably the most important factor to consider for a thorough assessment of an asset’s actual condition .
Though most power utilities rely on conductor sampling to perform such assessments, this is costly, time consuming and incomplete, only providing information from the sample location, probably the most accessible and not necessarily the most degraded place. Also, once the sample is taken, its evolution over time and rate of degradation can no longer be monitored. Non-destructive testing is thus a very promising approach for collecting useful data over much of the conductor’s length. Such testing must target the predominant aging mechanisms in order to provide an overall health index for assessment purposes.
Although generally very slow, the two predominant aging mechanisms in aluminum conductor steel reinforced (ACSR) cables are the loss of galvanic protection (zinc layer) around the inner steel strands, and fatigue breaking of aluminium strands at suspension clamps. To assess these two mechanisms, two technologies were selected, developed and deployed on Hydro-Québec’s power grid.
- LineCore is a compact, lightweight sensor head that injects high-frequency eddy currents around an ACSR cable. It acts as a transformer, with the inner-core steel strands ensuring electrical coupling between its primary and secondary coil. Zinc over the steel has a screening effect that reduces coupling proportionately to its thickness. The eddy current frequency is selected to maximize sensitivity for a zinc thickness range of 0 to 60 µm. The opening of the head is motorized so that it can be controlled from the ground, rolled over conductor splices and adapted for deployment either by being pulled by LineROVer, mounted on LineScout to cross obstacles or even mounted on unmanned aerial vehicles.
- LineScan is a non-radioactive X-ray device fitted onto an easily installed frame that can be adjusted to various line configurations. Line technicians can adjust its position and orientation so it can detect inner defects, such as broken strands at suspension clamps. Weighing about 10 kg and operated from the ground, LineScan can assess inner conditions within a few minutes so appropriate repairs can be made efficiently without sampling.
Unmanned Aerial Vehicles
IREQ’s robotics team has become increasingly interested over the past decade in the use of unmanned aerial vehicles (UAVs), or drones, for power transmission line inspection and maintenance .
After a slow start, the electricity industry is now actively interested in drones. The most widespread applications for drones are detailed visual inspection of transmission lines and 3D reconstruction from LIDAR data.
However, the electricity industry is still at the test and pilot project stage. Such technology is generally not yet part of today’s standard inspection and maintenance practices. Most transmission line owners consider that drones will not achieve their full potential until they can perform either urgent inspections over great distances after accidents and natural disasters or standard routine inspections with automatic defect detection capabilities. Both potential applications are hindered in many countries by legislation, which has failed to keep pace with the technology. Regarding automatic defect detection, some players are starting to develop solutions but great technical hurdles must be overcome to achieve the level of reliability and precision that the industry requires. Based on the considerable effort being invested in such solutions, though not yet mature, they should yield effective tools over the medium term.
Besides these standard applications for inspecting lines at a distance, in which the electricity industry is investing very heavily, some companies are exploring other approaches to meet specific needs and requiring contact with or transport of a line. One interesting application is the use of drones to help string conductors between towers. Other applications, like inspections involving contact and maintenance using drones, are very little developed on the international scene despite their great potential value to the industry. The inherent technical challenges being enormous, industry-specific and relatively neglected by industry players, this is the approach on which IREQ’s Inspection and Maintenance Robotics department has chosen to focus its efforts. For the past two years, the robotics team has been working on developing a drone capable of landing on transmission lines in order to use there the sensors and measuring instruments that provide the strategic data needed to properly diagnose the condition of lines and line components. A key team asset is its existing expertise in the design and fabrication of such measurement tools, which can be deployed manually or by robotic systems, and are thus perfectly adaptable to the constraints of drone deployment.
The IREQ-developed LineDrone  meets a number of criteria that make it an effective solution. First, the drone can turn off its main motors once on the line and use its specially designed motors/wheels to roll along the line and inspect it over long distances while consuming very little energy, giving it great autonomy once on the line. In addition, the pilot is assisted in landing on the conductor by an onboard perception/control system that detects the cable and keeps the craft hovering directly above the conductor, leaving the pilot free to concentrate on controlling the drone’s altitude for a safe landing. Lastly, the drone can be operated on live lines for optimal use. In 2016, the team demonstrated its ability to immunize a drone against interference from a 315-kV line. Its immunization work, now focused on the onboard perception/control system, should yield results in early 2018 and enable very flexible use of LineDrone.
State of the art
This section briefly overviews the state of the art in robotics dedicated to substations. Information is mostly drawn from more detailed references, including a paper by IREQ .
Ground robot systems to inspect substations were first introduced in Japan in the 1980s and have been used more intensively in China over the past decade. Figure 9 shows two robot systems, one from each of those eras. In order to be reliable, the first systems needed major investments in existing substations so robots could position themselves and navigate autonomously. Recent technologies have significantly reduced such investments. Thanks to progress in sensors (vision, LIDAR, IMU, GPS, etc.) and algorithms (sensor fusion, SLAM, etc.), self-positioning robot vehicles can now be used in substations with no significant modifications to existing infrastructure.
Other types of vehicles can also be used in the substation environment. Robots on cables have been tested. Drones are a potential solution for inspections at substations. Such vehicles deliver an aerial point of view, which can be valuable, generate 3D maps and, above all, can be deployed quickly and easily. However, drone solutions must be highly reliable and sophisticated to ensure personnel safety and infrastructure integrity.
Although substation-wide inspection with mobile robots is the main application that has been demonstrated and used to date, other applications promise great benefits to substation operators, and some field deployments have been reported. Insulator cleaning is one interesting application, with robots crawling and sliding on these components, removing dirt along the way. Systems from China and South Korea have been demonstrated. Also, EPRI proposes an innovative way of inspecting inside power transformers with a submersible robot that navigates through the oil tank . This is a short list of existing systems. As robotics and peripheral technologies continue to evolve, other field-demonstrated applications will emerge.
Substation Robotics at Hydro-Québec
IREQ foresaw that substations would be a great proving ground for robotics long before it was first applied in Hydro-Québec’s substations. Initiatives were sparked by a critical situation faced by the company in 2012: a problematic model of current transducer in use in numerous 735-kV substations across Québec meant that restricted areas had to be established for personnel safety. This severely constrained substation inspection and maintenance activities. To alleviate this situation, IREQ was mandated to quickly build a robotic inspection vehicle.
An initial robot system was developed and tested in substations in fall 2012. It consisted of a teleoperated unmanned ground vehicle (UGV) equipped with two articulated cameras: a 25X zoom inspection camera and a 640 x 480 pixel thermal imaging camera. Building on successful deployment of the first robot and faced with problematic locally operated disconnect switches in the restricted area of certain substations, Hydro-Québec asked that intervention capability be added to the robot system. In 2013, a second robot was thus developed and tested. The significant upgrades gradually added in 2013 and 2014 include the following:
- 6-DOF energy-efficient manipulator with a 1.5-kg payload, 90-cm reach gripper hand
- Wide-angle (180° x 180°) camera dedicate to navigation
- RTK GPS/GLONASS high-precision (±0.01 m) satellite-based positioning
- Significantly more powerful onboard computing
- Longer range wireless communications with better antennas
- Improved batteries with Li-ion technology, providing three times more energy
- Track-based traction system for operation in deep snow
- Weatherized components sustaining heavy rain and snow
- Proven operation at -20°C with an integrated 60-W heater for onboard electronics
Both robot systems counted on rugged, long-range 802.11g communications to ensure a robust teleoperation link in large restricted areas. For beyond line-of-sight operation, satellite-based global positioning was used. Both systems also integrated 3D LIDAR sensors for distance estimation. These sensors helped future-proof the systems by supporting possible autonomous navigation. Figure 10 shows both robotic systems.
For easy deployment, the robot is carried on site with and deployed from a mobile control station. A single operator can deploy and operate the robot with screens and controllers inside the control station. Figure 11 shows photos of robot deployment and operation in winter conditions. The first deployment, in fall 2012, demonstrated the system’s ability to perform visual and thermal inspections in the restricted areas of 735-kV substations. In fall 2013, the system demonstrated for the first time its ability to operate disconnect switches in restricted areas. During winter 2014, the system was tested to demonstrate its ability to operate in heavy snow and at -20°C. A total of ten deployments in five substations were completed during this three-year period. Hydro-Québec engineers found other ways to mitigate the impact of the restricted areas on day-to-day operations and the robot system was never used as much as initially thought. Nevertheless, field demonstrations were convincing and the robot system is still available to Hydro-Québec TransÉnergie. It is tested on a monthly basis to ensure that it is operational and ready to be deployed. Since critical situations may still arise unexpectedly, the robot system might quickly become the valuable tool it was initially meant to be. Further details on the robot system, its applications and deployment in Hydro-Québec substations are given in .
Opportunities for New Robotics Applications
Robotics is now becoming an essential technical solution in industrial applications traditionally less populated by robots: mining, agriculture, transportation, surgery, etc. This presence, combined with major advances in technology and algorithms, should reveal new opportunities to key players of the electric utilities industry and convince them to invest in robotic solutions and R&D. The following sections provide a glimpse of a few of these opportunities.
Mobile 3D Sensing and Intelligent Robotics
In order for a mobile robot to navigate autonomously and safely in a substation, probably amongst humans, onboard sensing, computing and ultimately intelligent capabilities must be highly advanced. This was not technically feasible a few years ago. That is why rails were used for the first substation inspection robots in Japan to ensure reliable, repeatable navigation. However, this solution was too costly. Today, with major technological advances in embedded computing capabilities, sensing and machine learning, autonomous robots navigating around us are a near-reality, self-driving cars being a great example.
A self-driving car navigating along streets and an autonomous robot navigating through a substation share much of the same technology, the latter being a somewhat simpler, specialized version of the former. The main components of a self-driving car are presented in . Whether on the ground or in the air, a substation robot could use similar subsystems. 3D sensing in a substation is one particularly important capability. First, it enables the robot to position itself. LIDAR would be one relevant device to accomplish this task. This device typically collects ranging data of objects at distances that may exceed 100 m, an important capability in a high voltage substation where objects are sparsely distributed. Stereo cameras are also useful for 3D sensing, particularly at shorter distances. A technique of 3D simultaneous localization and mapping (SLAM) will enable self-localization of the robot with these sensors. This technique could fill the gap in GPS-denied situations, which may occur in some portions of substations.
A SLAM algorithm will give the robot mapping capability, an attractive feature for a substation robot since a 3D map of the substation can be valuable to engineers. It can provide an as-built reference if one has not already been generated from terrestrial LIDAR, and update such references when changes occur in the substation (e.g., new equipment added). It can also be used when an incident occurs, for example a failure with debris or a storm. Lastly, 3D data can be used to automatically detect and localize specific substations components: transformers, insulators, circuit breakers, etc. This capability, demonstrated in , is a key factor in achieving autonomous inspections.
An intelligent robot physically demonstrates algorithms from the field of artificial intelligence (AI), more specifically from machine learning (ML) and deep learning. These areas of AI are covered well in . Recent advances in those areas make it possible to leverage two classes of mobile robot capabilities:
- Robot system functions, e.g., intelligent navigation and intelligent manipulation
- Intelligent data processing, e.g., automatic equipment diagnosis and defect detection
ML algorithms and 3D data processing place very high demands on computing resources. Implementing such capabilities in real time on a mobile robot is only possible because of recent advances in embedded computing power. Specifically, the use of graphic processing units as generic parallel computing devices gives rise to off-the-shelf embedded computers that can be dedicated to ML and 3D sensing.
Though only the beginnings of these advances are now apparent, since technologies and algorithms will continue to be pulled by markets like intelligent transportation. Some industrial products integrating all of the recent capabilities are appearing. For asset inspection on power grids, examples exist for power lines  and substations . The future is promising.
Integration of Existing Inspection and Diagnosis Technologies
As an inspection device, a mobile robot can carry a diversified set of sensors and thus accomplish multiple inspection and diagnosis tasks. Tasks already demonstrated include visual inspection and thermal imaging inspection. Much more is possible.
The idea behind this is to combine specialized sensors with the knowledge of field engineers and electrical technicians. As an example, 3D sensing can be used to measure slight changes in structural elements. Also, microphones can be used to detect pressurized gas leaks. The detection of SF6 leaks is particularly relevant not only for safety reasons but also for environmental protection. A specialized imaging device can be used to detect SF6 in air .
Detecting partial discharges is important as these are at the root of some failures of major equipment and thus costly shutdowns. External discharges, i.e., the corona effect, can be observed in the UV spectrum with specialized cameras. Internal discharges are more difficult to observe. RF-based analysis of electromagnetic emissions has shown convincing results for some specific substation components like circuit breakers and has been developed at IREQ as a non-intrusive technique . Partial discharge monitoring can also be deployed on mobile systems for more generic substation-wide monitoring . The antenna arrays used can easily be deployed on a mobile robot and existing techniques, and algorithms could conceivably be used to autonomously travel through a substation, monitor discharges and locate the main sources of emissions.
Looking farther ahead, a robot could be a sampling device in a power transformer oil testing program. A mini-laboratory could conceivably be developed and integrated to complete in-situ analysis. Ground grid testing is another interesting future application. A mobile robot could carry out measurements of ground resistance.
Robotic manipulation systems were first implemented to complete live work on distribution grids in the 1990s, not only in Canada, based on work at IREQ, but also in Japan and Spain. These first systems were only suitable at low or medium voltages. Similar work with hydraulic robotic arms but on high-voltage lines is now possible and has been recently carried out for live-line reconductoring of an entire 315-kV power line .
Similar high-voltage robotic manipulating capabilities will undoubtedly be exploited in substations, if this has not already done. Busbars, conductors and insulators are all components that could be manipulated with similar arms. In a less audacious scenario, a robot system capable of cleaning insulators and spraying them with silicone insulating material has been developed and demonstrated in China . Live work in substations should grow substantially in importance over the next decade given major refurbishment challenges throughout transmission grids, built during the same period in America and Europe.
Robotics as a Data-gathering Device
Monitoring databases are more than ever at the core of asset management. Electric utilities are investing vast sums of money in unified databases, more and more of them cloud-based. The cloud-based databases, often hosted by service providers, can now be connected to intelligent systems from the same providers. Artificial intelligence holds promise for use of this data to support much more optimal asset management decisions and actions. But in order to achieve this, these data-hungry systems must be fed the best data available, both in terms of quality and quantity.
A mobile robot system can prove to be a very reliable and precise means to collect and compile monitoring data. It can be used as a source of input to calculate health indices. Modeling power transformer aging is an example , where complementary data (more detailed thermal measurements, RF-based monitoring of internal discharges, etc.) could be gathered from a mobile robot.
Existing and future fixed sensors can help provide much of the data, but there will always be gaps to fill, valuable data missing. Synergy between integrated sensors, mobile sensing platforms like robots, and intelligent asset management systems should only continue to improve over a long period of time.
Significant benefits have already been reaped through the use of robotic technologies for inspection and maintenance tasks in various areas of the electric industry: underwater inspection of dams and embankments, in-situ refurbishment of hydraulic turbines, detailed non destructive inspection of live power lines, etc. Substations present an operating context for demonstrating high-value robotic tasks since they form a critical part of power grids and provide a challenging environment for inspection, maintenance and refurbishment jobs. Besides the fact that energized equipment must be maintained, substation components are subject to well-known degradation mechanisms, the symptoms of which can be monitored using existing inspection technologies. One of the challenges in inspection is to reach the proper components and position the appropriate sensors. Robotic platforms, such as unmanned ground vehicles, drones and other mobile robots, are definitely part of the solution.
Based on Hydro-Québec’s experience in successfully implementing robotic technologies in its operations, it is fair to say that the first step in substation robotics is to demonstrate the business case of a robotic approach. New robust compact technologies, artificial intelligence and recent developments in drone technologies all contribute to new, potentially high-value contributions for robotics in substations. Although inspection tasks seem to be the lowest hanging fruit, maintenance/refurbishment/construction tasks must not be overlooked, even if they present additional challenges in the perspective of live-line work.
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