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Transmission Line MaintenanceRobots Capable of CrossingObstacles: State-of-the-Art

Review and Challenges Ahead

Kristopher ToussaintDepartment of Mechanical EngineeringMcGill University817 Sherbrooke St. WestMontreal, QC H3A 2K6, Canada

Nicolas Pouliot and Serge Montambault∗

Robotics and Civil EngineeringHydro-Quebec IREQ1740, Boulevard Lionel-BouletVarennes, QC J3X 1S1, Canadae-mail: [email protected],[email protected]

Received 26 November 2008; accepted 10 February 2009

Power line inspection and maintenance already benefit from developments in mobilerobotics. This paper presents a comprehensive review of the state of the art. It focuses onmobile robots designed to cross obstacles found on a typical transmission line while usingthe conductor as support for traveling. Promising areas of research and development aswell as challenges that remain to be solved are discussed with a view to developing fullyautonomous technologies. Maintenance tasks, including inspection and repairs, are iden-tified as high-value applications in transmission live-line work. Conclusions are drawnfrom experience, and the future of mobile robotics applied to transmission line mainte-nance is discussed. C© 2009 Wiley Periodicals, Inc.

1. INTRODUCTION

Strategic assets such as transmission grids need tobe operated in a safe, predictable, and reliable way.To do so, maintenance strategies have evolved in re-

∗Serge Montambault has been project leader at Hydro-Quebec IREQfor the transmission line robotics research program since 1998. Hydro-Quebec generates, transmits, and distributes electricity, mainly usingrenewable energy sources, in particular hydroelectricity. IREQ providestechnical support to Hydro-Quebec’s divisions by carrying out techno-logical innovation projects in cooperation with universities, researchcenters, and industry. For further information, contact Mr. Montam-bault directly.

sponse to strict regulations and the inevitable agingof infrastructure. Recent blackouts and a steady in-crease in energy demand also put pressure on gridowners. Over the past few years, transmission linemaintenance practices have been significantly influ-enced by innovative tools and working methods. Asin many fields of application, robotics is making itsmark on transmission line maintenance.

Paula (1989, 1992), Earp (1996), and Parker andDraper (1998) were among the first to present acomprehensive review of where robotic applicationscan play a useful role to meet inspection require-ments in harsh environments. They identified robotic

Journal of Field Robotics 26(5), 477–499 (2009) C© 2009 Wiley Periodicals, Inc.Published online in Wiley InterScience (www.interscience.wiley.com). • DOI: 10.1002/rob.20295

478 • Journal of Field Robotics—2009

breakthroughs in fields as varied as nuclear powerplants, highway maintenance, railway inspection,aircraft servicing, and transmission and distributionnetwork maintenance. Montambault and Pouliot(2003) presented a literature review of innovativedevices applied to transmission line maintenance. Atthat time, among such novelties as new sensors andhelicopter-based methods, only a few robotic devices(all unable to cross obstacles) had found their wayinto real field operations. More recently, Dai (2004)reviewed a number of robotic inspection devices,including one prototype able to cross a dead-endjumper loop under laboratory conditions. Sincethen, all over the world, the number and variety ofreported initiatives with the goal of using reliablerobotic technologies under real transmission lineconditions have increased dramatically.

1.1. Transmission Line Maintenance: BusinessCase for Robotics

Just a few years ago, it was commonplace for a line-man to work on a deenergized power line. Nowa-days, live-line work is a must for most maintenanceoperations, and this need to maintain system avail-ability is a key factor in the business case for robotics.

Hard-to-reach locations such as spans crossingroads, rivers, railways, and electric distribution linesand spans through mountainous terrain are all placeswhere a teleoperated robot is invaluable. Indeed,reaching strategic locations to monitor the conditionof line components there leads to better asset man-agement. A better knowledge of the condition of as-sets results in optimal maintenance investment deci-sions, in avoided or deferred costs (e.g., by extendingthe life of assets), and in enhanced reliability.

Robotic technologies also have an impact onmaintenance personnel safety through remote ac-cess to energized components and the inspection andevaluation of the mechanical integrity of a damagedconductor prior to repair by linemen.

Compared to other methods such as helicopter-based work, using robots is often advantageousin reducing costs (twin-engine helicopter, fuel, pi-lot, and crew avoided), increasing efficiency (qual-ity of images and possibility of contact measure-ment), enhancing safety (of maintenance personneland the public), and providing access to specific cir-cuit configurations (e.g., vertical circuits, double cir-cuits, and lines through residential areas or vege-tation). Manned motorized trolleys also have their

limits when it comes to obstacle crossing (warn-ing spheres), travel along overhead ground wires(OGWs) (minimum dielectric clearance distance fromphases), and negotiating specific conductor configu-rations (e.g., vertical circuits and conductor bundles).Insulated boom trucks are useless for spans overswamps, farmland, and snowy terrain and difficult touse on such circuit configurations as vertical circuitsand very tall structures. A more in-depth discussionof the business case favoring robotics can be found inChan (2003) and in Montambault and Pouliot (2004).

1.2. Hydro-Quebec’s Early Work on RoboticsApplied to Transmission Lines

Since 1998, three different robotic technologies havebeen developed at Hydro-Quebec’s research insti-tute (IREQ) in an effort to introduce robotics intotransmission line maintenance practices. The first,LineROVer Technology, was introduced on the gridin 2000 and is described in Montambault, Cote, andSt-Louis (2000) and Montambault and Pouliot (2003).Although initially developed for deicing, this re-motely operated trolley is used on live 315-kV linesfor such maintenance tasks as visual and infraredinspections, measuring compression splice electricalresistance, and replacing old conductors and OGWsusing the cradle-block stringing method. The sec-ond technology, designed to operate on two-, four-,and six-conductor bundles, was developed in 2003(Pouliot, Montambault, & Lepage, 2004). Based ona very simple mechanism, the prototype device cancross obstacles found on conductor bundles, includ-ing spacer-dampers and suspension clamps, in about1 s. It was put on hold to develop an even more ver-satile system, the LineScout Technology, first used onthe Hydro-Quebec transmission network in 2006.

These technologies have been developed fromthe start with the involvement of the end users,i.e., linemen and line maintenance technicians fromHydro-Quebec TransEnergie. Introducing very sim-ple technology (i.e., LineROVer) helped robots gainacceptance in a traditional field of activity. Doing sosuccessfully depended on a good knowledge of lineconfigurations, existing working methods, strategictransmission line maintenance issues, and strategicstructures to focus on. A few design reviews were keyto implementing feedback from field maintenancepersonnel, and considerable work was invested inensuring the robustness and the electromagneticinterference immunity of the prototype.

Journal of Field Robotics DOI 10.1002/rob

Toussaint et al.: A Survey on Transmission Line Robots • 479

1.3. Objectives of the Paper

This paper focuses on mobile robots able to cross ob-stacles while using the conductor as their support intraveling. Alternative methods such as helicopters,unmanned aerial vehicles, airplanes, boom trucks,and motorized manned trolleys will not be discussedhere.

The authors’ intentions in preparing this state-of-the-art review are threefold as reflected in thethree-part structure. The initial third systematicallyreviews and summarizes recent findings. Some re-search teams have worked on complete systems, andothers have focused on particular subsystems or spe-cific functions. The middle third presents, from theauthors’ perspective, the remaining challenges andkey factors that must be considered along the pathto successfully implementing such technology un-der real field conditions. The final third of the pa-per presents several types of applications, some notyet developed, from which transmission line mainte-nance personnel could potentially benefit. In essence,whereas Section 2 is a typical literature review of anemerging field of research, Sections 3 and 4 can beviewed by the international robotics community asa plea to tackle the remaining challenges in orderto develop reliable, economically viable, and usefulclasses of new robotic applications. Section 5 brieflysummarizes a number of key findings and presents aschematic view of the overall context for the futuredevelopment of transmission line robots. Section 6concludes the paper.

2. REVIEW OF RESEARCH PROJECTS

2.1. Early Work

In the 1990s, a number of research teams pre-sented their work on mechanical designs to enablerobots to cross obstacles found on telephone, dis-tribution, and transmission cables. Among them,Sawada, Ishikawa, Kobayashi, and Matsumoto (1990)and Sawada, Kusumoto, Munakata, Maikawa, andIshikawa (1991) describe a wheeled trolley that car-ries an arc-shaped rail that extends to either side of atower and serves as a support to carry the trolley tothe other side. Although the prototype was never ap-plied in the field, time would show that the projectwas a pioneering effort in the domain. Aoshima,Tsujimura, and Yabuta (1992) presented a multisec-tion structure that is suspended from a telephoneline and can cross obstacles, including lateral lines,by pivoting the rear section around them. Tsujimura,Yabuta, and Morimitsu (1996) also proposed a sus-pended robot that “walks” along an overhead wireusing dual slider-crank mechanisms that were opti-mized kinematically to provide a stable gait. Theseauthors thus proposed various mechanical solutionsand suggested that they should become autonomoussystems dedicated to the inspection of power lines.Patents such as those of Kusafuka and Kitanishi(1991), Hanawa and Kobayashi (1994), and Ishikawa,Koshiyama, and Munakata (1997) also describebasic designs for devices dedicated to power line in-spection. Designs from early work are illustrated inFigure 1.

Figure 1. Early concepts: left, Sawada et al. (1991; c©1991 IEEE); center, Tsujimura et al. (1996; c©1996 IEEE); and right,Ishikawa et al. (1997).



2.2. Complete Systems

Among the various projects that exist in this field ofrobotics, only few resulted in validated prototypesthat are close to implementation or highly developed.This section presents two exceptions in order to intro-duce key aspects of the technology, further discussedlater in the paper.

2.2.1. Chinese Academy of Science

The Chinese Academy of Science (CAS), in collabo-ration with other academic institutions, has been anactive player in the development of such technologyand has several collaborating teams working in par-allel on a number of projects.

Among the most advanced of these projects isa dual-arm robot designed for live-line inspectionof extra-high-voltage power transmission lines (seeFigure 2). As presented by Wang, Fang, Wang, andZhao (2006), this platform is designed to hang fromthe OGW on its two wheeled arms, in order to havean optimal view of the conductors below. Inspectionsuse a video camera pointed downward at the lines.The length of the arms adjusts to keep the robot hori-zontal and help keep the distance between the cameraand its target constant.

Each of the two wheels is equipped with a grip-per that can securely grasp the conductor. The hous-ing containing electrical and electronic componentscan be shifted forward or backward to center themass on either of the two arms, as explained in Zhu,Wang, Fang, Zhao, and Zhou (2006a). An earlier ver-sion of the prototype and the governing kinematicequations were presented by Wang, Wang, Fang, and

Zhao (2005) and Zhang, Zhang, and Jian (2007). Initialsimulations and design optimization are described bySun, Wang, Zhao, and Liu (2006).

This technology has two different methods ofcrossing obstacles. The first, referred to as the“cankerworm method,” consists of centering themass on the rear arm, lifting the front wheel, movingforward until the front has cleared the obstacle, andthen setting the front wheel back onto the conductor.The same process is repeated for the rear. Using thesecond method, once the robot is near the obstacle, itcan grip the wire with the front gripper for stability,lift and rotate the rear laterally to the opposite sideof the obstacle, and then repeat the process for thefront arm. These sequences and the associated controlmethods are presented in Zhu et al. (2006b, 2006c).

These methods enable the robot to cross coun-terweights and crimp connection pipes and, usingthe second method, single overhead anchor clamps.Because the two arms are 240 mm apart, pairs ofanchor clamps separated by a sufficient gap for oneof the wheels can also be crossed in sequence. Theprototype weighs 40 kg and travels at up to 2 m/s.To ensure safe operation, a motor current watchdogwas implemented to detect any abnormalities andimmobilize the unit until the situation could beanalyzed by an operator. A prototype has been testedin the field but the research team plans to further testits reliability under windy conditions.

Its control scheme is based on an expert systemthat uses information from various onboard sensorsand a static database to attempt to navigate alongtransmission lines autonomously. When the robotencounters an obstacle on its path, it matches it toa six-bit code to which a motion sequence can be

Figure 2. CAS prototype presented in Zhu et al. (2006, 2006b; c©2006 IEEE).



associated. Two distinct methods were developed toenable the gripper to locate the ground wire whenreembarking onto it. The first, described in Zhu et al.(2006c), uses two laser sensors on each gripper. Thesecond, described in Wang, Wang, and Fang (2007),uses the video signal from a single microcameraon each gripper. For this method, stereovision wasdeemed unnecessary because the distance to theconductor is a function of the ratio of the apparentto actual (known) wire diameter. The control systemhas not been fully tested, but Sun, Wang, Zhao, andLing (2007) have proposed precision enhancementmethods.

2.2.2. Hydro-Quebec LineScout

The LineScout Technology developed at Hydro-Quebec’s research institute (IREQ), shown inFigure 3, was first presented by Montambaultet al. (2005) and then by Montambault and Pouliot(2006). The latter paper was selected to appear inMontambault and Pouliot (2007a).

The two-wheel LineScout platform can cross ob-stacles by deploying a two-gripper auxiliary frameunder the cable and securing a grasp on both sides ofthe obstacle. The traction wheels can then be releasedfrom the conductor, flipped down, and moved to theother side of the obstacle. The geometrical analysisunderlying the optimization of the platform’s struc-ture was detailed in Pouliot and Montambault (2008).

The mobile robot is designed to travel alongsingle energized conductors, including one of the

conductors of a conductor bundle, and is immunizedto electromagnetic and radio-frequency interfer-ences (EMI/RFI) from lines of up to 735 kV. TheLineScout’s obstacle-crossing sequence takes lessthan 2 min and is versatile enough to clear obstaclesup to 0.76 m in diameter and most series of adjacentobstacles. Such obstacles include warning spheres,spacer-dampers, and single- and double-suspensionclamps. Crossing dead-end structures and jumpercables was not included in the design specifications.LineScout’s top speed is 1 m/s, and its weight is98 kg. To the authors’ best knowledge, this is the firstand only robot of its kind that has been successfullyused in the field to date. The thorough validationto which LineScout was subjected is described inMontambault and Pouliot (2007b), and the methodsassociated with its field deployment can be found inMontambault and Pouliot (2008).

The decision was made to control the robot in ateleoperation mode, whereas systems were designedto later shift to an autonomous mode. LineScoutrelies on a variety of sensors for control and safety:three programmable pan-and-tilt cameras (PPTC),inclinometers, and motor encoders keep track ofattitude. The core of the control system, at the op-erator’s ground station to which information fromthese sensors is sent, is a LabVIEW program andinterface. To simplify and ensure safe control of its11 motors (excluding the PPTC motors), it makes useof a mode operation strategy (MOS), which limitsthe number of actuators being controlled, dependingon the specific task mode. Also, software interlocks

Figure 3. LineScout on a live 315-kV line.



override potentially hazardous instructions. To fur-ther facilitate control and inspection, preset targetsenable LineScout to point its cameras to key locationson the conductor, taking the configuration of theframe attitude into account.

In addition to having visual inspection devices,LineScout is equipped with a variety of sensors andmaintenance tools. The range of tasks that LineScoutcan perform was recently expanded with the addi-tion of the dual-end-effector arm module (Pouliot &Montambault, 2009). Whereas the near end of the armis reserved for instrumentation, the far end is de-signed to accommodate a fourth PPTC. Thus far, atool to temporarily repair broken conductor strandsusing annealed copper clamps, a universal electrictorque wrench, and an electrical resistance measure-ment sensor are all instruments that can be used.This technology has been successfully deployed onseveral occasions when other methods were notpossible.

2.3. Work on Specific Subsystems

Mobile inspection robots are complex systems thatcan be seen as assemblies of subsystems responsiblefor aspects such as locomotion, control, and sensors.Although they may not have produced complete sys-tems like the technologies mentioned above, many

active research teams have made significant progressin one or more of these aspects.

2.3.1. Approaches to Locomotionand Obstacle Crossing

Expliner, currently under development as a jointproject by Kansai Electric Power Corporation(KEPCO) and Hibot Corporation, among others, is anovel method of crossing obstacles, as presented byDebenest et al. (2008). When it reaches an obstacleon its path, Expliner makes use of an actuated armthat positions a counterweight beneath it so that itcan raise each of its two wheel sets in order to pivotthem to the other side of the obstacle. Expliner istargeted for live-line work with EMI/RFI immunityup to 500 kV and is compatible with single cablesand with two- or four-conductor bundles. For workon bundles, the robot is installed on the two topconductors and can roll over most models of spacer-dampers. The authors presented the key conceptbehind teleoperated control of the prototype. Theydescribed the functioning prototype in detail, statingits mass (84 kg), dimensions (500 × 1,060 × 715 mm),and speed (0.6 m/s). Possibly because they workclosely with a power utility, the authors are amongthe few who actually proposed a live-line installationmethod. As shown on the right-hand side of Figure 4,

Figure 4. KEPCO’s Expliner prototype shown on a four-conductor bundle with details of its mechanical modules (left)and its novel installation strategy (right) (Debenest et al., 2008; c©2008 IEEE).



it is possible to secure an insulated rope onto the liveconductor and tension it from the ground. The robotcan then climb along the rope and transfer onto theconductor using its crossing strategy. Though pre-liminary tests have been successful, several features,e.g., weight redistribution, EMI/RFI shielding, andadditional sensors, must be introduced or improvedbefore it is fully functional and can be used in thefield.

Rocha and Sequeira (2004) presented a feasibil-ity study for a simple brachiating concept wherebya two-arm robot is suspended on the conductor andpivoting links allow one arm to leave the conductorand grab it again on the other side of the obstacle.The control approach and results from dynamic sim-ulation were presented.

Resulting from a joint effort by the Escola Su-perior de Tecnologia de Setubal and the InstitutoPolitecnico de Setubal, Tavares and Sequeira (2004)described a technology named “RIOL” that was de-veloped by building on the work of Rocha but intro-duced a third arm in order to obtain realistic motortorques (see Figure 5). The locomotion gait achievedthrough a 10-step process is described, along withsimulation results and the preliminary design of apolyvinyl chloride (PVC)–tubing prototype.

Tang, Fang, and Wang (2004a) and Liang, Li,and Tan (2005) both presented tribrachiation systemsdeveloped at the CAS. The multi-degree-of-freedomstructure shown in Figure 6 allows a minimum of twotraction wheels to be secured to the cable. For verysteep slopes, the system presented can change howit travels from rolling to squirming. Each arm has a

Figure 5. RIOL crossing strategy (Tavares & Sequeira,2004; c© 2004 IFAC).

Figure 6. CAS tribrachiation system, from Zhou et al.(2005; c©2005 IEEE).

grasper at the end, and these can alternately clamponto the line to avoid sliding. Automating this modeof traveling, however, was not attempted. In reportedlaboratory experiments, the prototype can cross sus-pension clamps autonomously in about 15 min evenwhen the line changes direction.

De Souza et al. (2004) and Becker, Landre, andSantos (2006) published similar papers in which theyinvestigated several possible architectures for linecrawler robots. The former went as far as to analyzethe perturbing effect of wind gusts on the architec-tures, and the latter generated various robot designsand performed a theoretical feasibility study on each.

Rothman (2006), working with ABB Research,Ltd., described a two-part buggy that rolls ontothe conductor and keeps its balance using counter-weights to either side. Approaching an obstacle, therear part is released from the conductor and pivotedby 180 deg in a horizontal plane. The other partcan then move similarly to complete the crossingsequence.

Recently, Wu, Xia, and Lai (2007) introduced an-other type of mobile architecture dedicated to powerline inspection, referred to as the “wheel-claw hybridmanipulator.” This architecture presents two-drivewheels and numerous grasping units operated by atension cable in a somewhat underactuated manner.Grasping stability is analyzed, but prototype designdetails have yet to be published.

2.3.2. Computer Modeling and Simulations

Certain researchers have focused their work ondeveloping numerical models and simulations tovalidate and optimize a design.



Figure 7. Models used in simulations: left from Xiao et al. (2007; c©2007 IEEE) and right from Nayyerloo et al. (2007).

Lagrange’s equations that drive the dynamicsof all the joints of the two-arm platform shown inFigure 7 (left) were derived in Xiao, Wu, Du, and Shi(2005). Work has been presented in Xiao, Wu, Wang,Xie, and Li (2006), Xiao, Wu, and Li (2006), and Wu,Xiao, and Li (2006) to simulate the dynamic couplingbetween this (assumed rigid) platform and the flex-ible line using Pro/E and ADAMS. Modal vibrationanalysis performed by finite element analysis (FEA)using ANSYS is presented in Xiao, Wu, and Li (2007)and in Figure 7 (left). A publication presenting themechanical design of the platform in English couldnot be found, but it seems very similar to the one pre-sented in Dai (2004) and reused by Fu, Zhang, Cheng,et al. (2006) and Fu, Zuo, et al. (2008).

An alternative to rolling on the conductor is thepassive brachiating motion, which consists of alter-nately swinging each of two arms forward like amonkey from branch to branch. Work has been doneto implement this type of motion in line maintenancerobots at the Universidade Federal do Rio Grandein Brazil by De Oliviera and Lages (2006a, 2006b).The advantage of this form of locomotion is its abil-ity to exploit gravitational forces, which increases ef-ficiency and therefore reduces power requirements.This project is still in the early stages of develop-ment and, in our opinion, will be very difficult toreliably apply to the unpredictable environment ofpower transmission grids.

Jian, Tingyu, and Guoxian (2008) present a simpleyet effective simulation that governs the centroid bal-ance of a two-arm platform. The principle is to con-

trol the position of the electronics box at the bottomof the platform so that the resulting centroid locationis close to the supporting arm.

Nayyerloo, Yeganehparast, Barati, and Foumani(2007) of Semman University, Iran, presented a three-arm architecture called MonoLab. Validation of thecrossing strategy was obtained by an ADAMS dy-namic simulation (Figure 7, right), and a scaled-downprototype was assembled for preliminary laboratorytesting.

2.3.3. Control Strategy

A distributed expert system (DES) based on the Clanguage inference production system (CLIPS) wasdeveloped by the CAS and is implemented on thetribrachiating platform shown in Figure 6, as ex-plained in Zhou, Wang, Li, Wang, and Xia (2005),Tang, Fu, Fang, and Wang (2004), and Tang, Fang,and Wang (2004b). The philosophy behind the con-trol system is based on the fact that transmission linecomponents are only slightly variable. Therefore, adatabase containing information on obstacles can bebuilt, enriched during operation, and used to navi-gate the grid autonomously. The DES is composed ofthe CLIPS inference engine, a CLIPS knowledge base,a static database, an external information input mod-ule, and a decision-making module.

The control system can operate in two distinctmodes: autonomous layered control and direct con-trol, which is a form of teleoperation. The layeredcontrol has four layers: the task layer, subtask layer,



Figure 8. Two-arm vehicle (Cai et al., 2008; c©2008, IEEE).

movement planning layer, and execution layer. Whenoperating in layered mode, the robot’s sensors detecta counterweight at the end of the ground wire, whichinitiates navigation sequence planning. Informationon the current obstacle is retrieved from the database,which is referenced by order of towers. A motion se-quence is then generated, and commands are deliv-ered to the motors. In complex situations, this maynot be possible and direct control is required. Whena type of obstacle is first encountered, it may take along time to cross, but the procedure is “learned” andthe process is much faster for subsequent encounterswith the same obstacle.

More recently, Cai, Liang, Hou, and Tan (2008)presented another two-arm vehicle that crosses obsta-cles by transferring a fair amount of its weight (theelectronics unit) beneath the supporting arm so thatthe other (rear) arm can be raised and then pivotedto the other side of the obstacle, as shown in Figure 8.No mechanical details are provided. The authors de-scribe, however, a fuzzy controller that commandsthe turning behavior of the robot, with a very simpli-fied mathematical model. The intention is to separatethe obstacle-crossing process into a dozen simplersteps. The stability of the fuzzy controller is assessed,and the performance is found to be superior to that ofa regular proportional-derivative (PD) controller.

2.3.4. Obstacle Detection, Classification,and Identification

This aspect is an essential step toward introducingsome degree of autonomy. To achieve obstacle detec-

Figure 9. University of Manitoba LCR concept (Peterset al., 2002, Fig. 2), with kind permission of Springer Sci-ence & Business Media.

tion and classification, Peters, Ahn, and Borkowski(2002) from the University of Manitoba, Canada, usedseveral arrays of proximity sensors, installed on thebody and legs of their line-crawling robot (LCR),shown in Figure 9. Information from these sensorsis then analyzed with a neural classification sys-tem. Using several predefined threshold values, ob-stacles are then assigned to a class to which a set ofobstacle-crossing commands is associated. In Peters,Ramanna, and Szezuka (2003), the authors presentedvariations on the algorithm and concluded, throughsimulation results, that the technique is promising.

At the CAS, Fu and his team of collaborators havebeen very active in developing features that breaknew ground in the area of obstacle detection andrecognition for future transmission line inspectionsystems. The robot they built uses charge-coupleddevice (CCD) camera vision and three-dimensionalreconstruction to extract the edges of lines, circles,and ellipses from the images, as explained in Zhanget al. (2006), Fu, Li, et al. (2006), and Fu, Liang, Hou,and Tan (2008). These two-dimensional features arethen used to detect and discriminate between obsta-cles such as suspension clamps, strain clamps, andcounterweights. Placing the cameras below the con-ductors and pointing them at an upward angle pro-duces a simpler background, which facilitates targetedge extraction. Obstacle recognition has been shownto work in the laboratory and in the field under goodlighting conditions.

Interesting work that applies previous efforts toreal field conditions is presented by Fu, Zhang, Zhao,et al. (2006) and Fu, Li, et al. (2006). In these papers,



Figure 10. Line component identification: insulator dish(Fu, Li, et al., 2006; c©2006, IEEE).

the authors presented an efficient deblurring algo-rithm that estimates the motion due to the (unavoid-able) vibrations of the camera and uses neural net-works to restore image sharpness. Finally, Fu, Zuo, etal. (2008) presented results toward obstacle identifica-tion, where a self-learning algorithm manages to cat-egorize and segregate insulator strings from the con-ductor or spacer-dampers. Some graphical results areshown on Figure 10.

2.3.5. Energy Harvesting from the Power Line

Getting energy directly from the power line is seen bysome researchers as a promising solution. Some pre-liminary work, similar to a feasibility study, was pre-sented by Peungsungwal, Peungsiri, Chamnongthai,and Okuda (2001). In that brief paper, a simple two-wheel motorized robot could travel at a speed of3 m/s, drawing a 200-A ac current from the line. SanSegundo, Fuster, Perez, and Mayorga (2006) also pre-sented an encouraging demonstration of the feasibil-ity of such a process when they managed to power a24-V dc motor from a 300-A ac current. Both teams in-duced an ac current by placing a torus-shaped devicearound the conductors, but no data could be foundon the power collected.

2.4. Other Technologies of Interest

In Ruaux (1995), Electricite de France presented aconcept and design specifications for an automaticmachine dedicated to warning sphere installation.The system was to be mounted onto the conductorsby means of a helicopter. Campos et al. (2002), from

Universidade Federal de Minas Gerais in Brazil, pre-sented a technology dedicated to warning sphere in-stallation. Once installed on the span, the robot is tele-operated to reach the desired location of the warningsphere, where it can then install or remove a spherewithout any further operator intervention. Field test-ing was successfully performed. The proposed sys-tem, however, lacks the capacity to cross obstacles.

Jones (2004, 2006), from the University of Bangor,UK, is working on a concept of an uninhabited airvehicle (UAV) that uses ducted counter-rotating fansto hover over distribution lines for inspection. Al-though it does not travel on the conductors directly,it maintains contact with them in order to draw itspower and loses contact only when it reaches an ob-struction in its path. The technology’s limited auton-omy during free flight exempts it from British avia-tion regulations. Golightly and Jones (2005) presentedan artificial vision algorithm that effectively controlsthe position and attitude of this UAV with respect tothe power lines and does so even in the presence ofgusty side winds. Experimental results were obtainedwith a small-scale laboratory mock-up of a distribu-tion line.

Finally, Luo, Xie, and Gong (2005) and Luo, Xie,Gong, and Lue (2007) presented a maintenance robotdeveloped at the University of Shangai to travel alongthe cables of cable-stayed bridges. Even though thistechnology does not aim to cross obstacles, the mod-ularity of the design, in addition to the maintenancetasks it already performs under real field conditions,makes it a noteworthy example of the future poten-tial of any cable robot. Its ability to apply paint and todetect rust on inner strands is of particular interest.

3. PROMISING FIELDS OF RESEARCHAND DEVELOPMENT

As demonstrated in preceding sections, very impor-tant steps have been achieved in addressing someaspects of operating a robot on live lines and cross-ing obstacles on them. However, many issues havenot yet been studied and great challenges must stillbe met to implement autonomous transmission lineinspection robots.

3.1. Specifications for Robots Dedicatedto Live Transmission Lines

The most important issue that applied robotics mustaddress is related to operating conditions in the field



and their impact on robot design. Incorporating thefactors in the sections below into the technical speci-fications for the initial design can make the differencebetween a product for laboratory development andone producing tangible benefits for operators.

3.1.1. Working on Strategic Assets: Reliability Issues

More than in many operating contexts, working ona live transmission grid means that systems must bedesigned, tested, and found to operate in a safe, pre-dictable, and reliable way. Such events as damagingcomponents, creating an unplanned service interrup-tion, or jeopardizing public safety should be inputs toa rigorous process of failure mode and effect analysis(FMEA). Configuration changes can be made withinthe life of a previously validated prototype, but theeffect of any modification must always be assessedfrom a reliability standpoint. When necessary, vali-dation testing must be repeated. Preventive mainte-nance, preinstallation checklists, and close battery lifemonitoring are further examples of what should becovered by standard work procedures to ensure therequired reliability.

3.1.2. Robustness

Severe design constraints come from the working en-vironment of live power lines. If not waterproof, therobot must be splash proof (light rain, snow). Typi-cal ambient working temperatures will vary between−20◦C and +40◦C. The design must also take into ac-count conditions such as dust, snow, and UV radi-ation and mechanical shocks that will occur duringtransportation (all-terrain vehicle, snowmobile, heli-copter, etc.) and the installation procedure (collisionwith the tower, etc.). On some occasions, robustnessshould be prioritized when selecting components forthe robot. For instance, the choice of high-end sensorsshould be ruled out if they are not robust enough andcannot be adequately protected.

3.1.3. Live-Line Working Capabilities

Electromagnetic interference is another major designconstraint for onboard electronics, telecommunica-tion systems, and peripheral systems such as sensorsand cameras. These constraints have a huge impacton board design (effect of magnetic fields), geometricdesign (minimizing the corona effect due to electricfields), and overall grounding and shielding strategy.

Conductivity in every mechanical component shouldbe maintained to avoid any electrical dischargewithin the structure. Overall dimensions and totalweight also play a critical role in the live-line work-ing capabilities because these features will affectsafe dielectric clearance when crossing the toweror at midspan, due to the inevitable increased sag.Because 1,200-kV systems should eventually becommissioned in China, developers should aim forrobots capable of working under the correspondingelectric field value. One should also expect therobot to evolve in the magnetic field associated with2,000-A current.

3.1.4. Installation Methods

Successfully implementing robotics in the field de-pends primarily on the level of knowledge of ac-tual operating conditions under which the technol-ogy will be used. End-user feedback and input, aswell as existing tools and working methods, mustbe considered as important guidelines in the earlydesign of the technology, specifically in developingthe man–machine interface. Any need to install asomewhat sophisticated technology on an energizedpower line from a safe dielectric distance several feetover the ground using insulated hot sticks will have amajor influence on the design. Health and safety reg-ulations and local codes should also be studied, whenapplicable. Various installation and retrieval methodsmust be considered, such as helicopters and insulatedboom trucks. Figure 11 presents three examples of dif-ferent installation methods for the LineScout project,all validated and performed by linemen.

3.1.5. Payload Capability

Getting a robot to efficiently roll along a conductorand cross obstacles remains the main technical chal-lenge in implementing mobile robots on power lines.However, the main purpose of having robots on astructure is to perform useful, difficult, or otherwiseimpossible tasks. To do so, the higher the allowablepayload of the mobile platform, the higher the valueof the technology because it will be possible to installa greater variety of sensors or modules. Design con-straints described earlier (such as overall weight anddimensions) have an adverse effect on the payloadlimit. Special efforts must be made to minimize theseconstraints, especially if maintenance work is theobjective.



Figure 11. Installation methods developed and validated by line maintenance personnel, using insulated boom truck on a69-kV circuit (left) and using insulated rope on a 735-kV line (center) and on the OGW above double 315-kV circuits (right).

As an example, a robust sensor dedicated to livepower line maintenance is likely to weigh a bare min-imum of 7 kg. With the addition of the deploymentmechanism, associated motors, and proper shield-ing, one obtains a prospective payload of 15–20 kg,which can easily represent 20% of the total weight.Proper functioning of the moving platform, includ-ing its obstacle-crossing capability, should then not bedrastically affected by this payload.

3.1.6. Crossing Jumper Cables, Dead Ends,and Angle Structures

In Montambault and Pouliot (2006), a systematicanalysis was made of the obstacles to be crossed ona transmission line. Based on the breakdown of ob-stacles encountered and on which kind of line theywere found, a business case was built to determinewhether crossing a particular type of obstacle madeit worth considering that obstacle as a design con-straint despite the impact on system complexity, com-pactness and weight of the robot, control issues, elec-trical clearance needed for live-line work, reliabilityof the systems, etc. This exercise should always beperformed and validated for each type of applica-tion. Dead-end and angle structures, such as shownin Figure 12, are a special case and must be examinedclosely.

If the goal is an autonomous vehicle capable of in-specting hundreds of kilometers of lines without hu-man intervention, one has no choice but to addressthe problem of crossing dead-end towers. This is ahighly strategic decision because it is likely to imposea physical limit on the maximum size of the obstacle

Figure 12. Jumper cables located at an angle tower.

that can be crossed. Interestingly, several robot archi-tectures proposed in Section 2 avoid this limitation byrunning only along OGWs (where no loose strandsare usually installed). However, in such cases, theauthors lean toward developing strictly autonomousline inspection robots instead of potential mainte-nance robots.

3.2. Battery Technologies and RechargingStrategies

Many factors influence the choice of the optimalpower supply: instant power needed, total energyneeded for sufficient autonomy, weight limit, oper-ating temperature, specific safety-related issues, type



of actuators, sensors used, etc. As with most reportedtools, LineScout uses electric motors. Therefore, theanalysis clearly pointed toward an electric powersupply. Gasoline generators were excluded based oninstant power requirements (up to 600 W) and safetyissues. The choice was made to use a battery for on-board power. Technology is progressing very quicklyin this area but a Li-ion battery remains the bestchoice for up to 1 day of energy autonomy.

Assembling a reliable and efficient mobile on-line induction module remains a challenge. A batteryis still likely to be required to provide instant peakpower and energy during obstacle crossing, to offerthe possibility of working on a deenergized line orthe OGW, etc. At present, recharging the battery us-ing the energy recovered on downward gradients, us-ing the power line’s electric field, and installing solarpanels or a wind turbine all seem, at best, a means ofincreasing autonomy, not of becoming the sole energysource.

3.3. Telecommunication Systems

Telecommunication systems selected must complywith local regulations (type of technology, frequency,and power level) and remain reliable under severeconditions of electromagnetic interference. Achievinga fully autonomous robot capable of inspecting lineshundreds of kilometers long without human inter-vention probably excludes line-of-sight systems, un-less repeaters are used. To overcome this constraint,Liang, Li, Tan, Liu, and Rees (2005) demonstratedthe feasibility of operating an inspection robot basedon wireless local Internet. Of course, for transmis-sion lines located in very remote areas, a broadbandsatellite Internet link should be established, which re-quires cumbersome dish antennas and greater powerconsumption. A means of avoiding this would be toincrease onboard computational power and auton-omy, which, on the other hand, could decrease therobot’s robustness and reliability.

3.4. Obstacle Detection and AutonomousCrossing

Although numerous studies related to power linerobots have been produced, only a small number ofteams have tackled the objective of obstacle detec-tion and recognition (see Section 2.3.4). This step is,however, essential both for designing an autonomousrobot and for safely operating it.

Even in teleoperated systems, obstacle detectionis an interesting safety feature to avoid mistaken op-erator commands. However, such a system shouldbe 100% reliable at detecting, from a reasonable dis-tance, anything differing from the supporting cable.Large-diameter aerial markers, suspension clamps,and even vibration dampers can be easy to detect dueto their size. Furthermore, these components are lo-cated at predictable locations and may be stored in adatabase. Broken strands due to lightning strikes andmidspan compression splices, however, may be lo-cated anywhere along spans and could greatly ham-per the line robot’s progress if undetected. Such“obstacles” are much more challenging to detect andshould be part of the detection system specifica-tions. False detection that requires operator confirma-tion should be tolerated given the consequences ofnondetection.

A great deal of work remains to be done, notablyin areas such as sensor design, sensor fusion, vision,and computing. Results for image deblurring are en-couraging because vibrations will inevitably causenoisier signals from sensors.

Once obstacle detection, sizing, and recognitionare achieved, autonomous crossing is the next step.Designing robust algorithms that allow obstacles tobe crossed unmonitored by an operator is a challenge.Running into unexpected obstacles is more frequentthan usually suspected on an aging power line. Also,there are many possible series of obstacles, makingobstacle-crossing strategy a complex matter, becausecomponent integrity, public safety, and service con-tinuity are on top of the priority list. The change inhorizontal angle of the conductor at a lattice structuremay make it a challenge to find the conductor at theother side of the suspension clamp.

As numerous electric utilities have already builta georeferenced database of the major transmissionnetwork equipment (i.e., towers), the introduction ofan onboard global positioning system (GPS) wouldallow logging any findings such as defects into thesame georeferenced database, allowing efficient useof the gathered information for optimal maintenancestrategy.

3.5. Status of Research

Technologies now vary greatly in their level ofadvancement. Some studies are applied; othersare theoretical in nature. Different challenges arebeing addressed by different teams. This seems very



Figure 13. Fields of research required to achieve the actualapplication of transmission line robots.

promising because complementary and collaborativeefforts could emerge under such conditions.

Figure 13 illustrates the different levels of techno-logical advancement that would lead to usable trans-mission line robots. The figure also indicates quali-tatively where results are numerous (shaded boxes)and where there is still room for a wide range of orig-inal work (white boxes).

As suggested by the figure, a moving platformmust be equipped, minimally, with application mod-ules. The combination of both platform and mod-ules must comply with transmission line specifica-tions, and this must be thoroughly validated before itcan be applied. In other words, even if advanced fea-tures such as autonomous crossing and obstacle de-tection are likely to be introduced in very advancedrobots, sound and simpler teleoperated technologies,equipped with valuable application modules, shouldbe validated and introduced progressively into linemaintenance practices. This would generate positiveexperiences, increase the developers’ field of exper-tise, and initiate the technology acceptance process.

Progressively, advanced features are likely to beintroduced in previously validated systems in orderto enhance their performance. The same technolog-

ical enhancement should take place for applicationmodules. As presented in the next section, mainte-nance activities are within the reach of transmissionline robots but should be preceded by inspectionactivities.

4. FUTURE APPLICATIONS IN TRANSMISSIONLINE INSPECTION AND MAINTENANCE

This section covers the future of transmission linerobots and attempts to list new potential applicationsthat could benefit electrical utilities. Being part of amajor electrical utility, the authors have a privilegedvantage point to anticipate these needs, as expressedin Montambault and Pouliot (2004). However, otherorganizations throughout the world are reaching sim-ilar conclusions, such as Earp (1996), Chan (2003),BPA (2006), BCTC (2008), and Vadakkepat andJanardhanan (2008). Potential applications are bro-ken down into two categories: inspection andmaintenance.

4.1. Inspection and Sensors

As a robot progresses along a power line, its mainpurpose is to be able to inspect its environment. Re-trieved information is later analyzed offline and willultimately serve as a basis for automated power linecomponent diagnostics. In fact, a wide variety of sig-nals could be collected: visual, electrical, thermal, au-dible, etc. Jiang and Mamishev (2004) reviewed tech-nologies applicable to underground power systemmonitoring, most of which can also be applied tooverhead transmission line diagnostics.

4.1.1. Visual Information

As with many fields of inspection, visual informationremains the most common, practical, and easilycollected data. In transmission line maintenance,visual data provide important information of manytypes: defective components (insulators, vibrationdampers, spacer-dampers, corona rings, warningspheres, splices, and structures), broken strands,corrosion of structures, vegetation encroachingupon the right-of-way, etc. Allowing a team of linemaintenance personnel to view and discuss thisinformation at ground level is also very worthwhile.Furthermore, archiving such information for futureconsultation or use in field reports is of even morebenefit. Figure 14 gives typical examples of line



Figure 14. Typical line component images collected by robotic inspection.

component images collected over the years usingrobots. Remaining work in visual inspection includesthe development of high-resolution yet compact androbust cameras, image stabilizer algorithms, etc.

4.1.2. Specialized Sensors

Commercial sensors, used and validated by linemenand developed by specialized companies, are avail-able as commercial products. Whenever possible,robot developers should seek to equip their mobileplatforms with such sensors, in a modular way. Theremaining challenge is then to pick up and archivethe data flow emanating from the sensors. Managingthe extra payload and extra volume associated withsensors can also be a challenge. Following is a list ofexamples of such sensors.

• Splice electrical resistance measurementCompression splices are line components thatneed to be evaluated on a regular basis. Be-cause measuring the electrical resistance isthe most direct and precise way of evaluatingthe condition of a splice, it is the first appli-cation module that was implemented on linerobots (Montambault & Pouliot, 2003).

• ACSR steel core corrosion detectionIn some parts of the world, high humidityand salt air combine to accelerate corrosionof the steel core of ACSR (aluminum con-ductor steel reinforced) cables. Different sen-sor technologies are known to be effective indetecting corrosion or the loss of the galva-

nized coating. Eddy-current sensors are usedin some commercially available technologies,but other technologies are also emerging.

• Broken strand detection (inner layer)Aluminum strands of the inner layer of ACSRcables sometimes break, most of the time nearsuspension clamps, splices, and other areasof high mechanical stress. Some technolo-gies seem to detect such strands under cer-tain conditions, but extensive measurementprograms still need to be conducted for val-idation. Portable X-ray sensors are among thepotential technologies to be examined.

• Insulator dielectric verificationA few sensors exist for validating the dielec-tric strength of insulators. Instead of climb-ing every support structure to check insula-tors, linemen could use teleoperated robots toaccess insulator strings. Performing this taskon a live line clearly presents the challenge ofavoiding flashover because insulators need tobe electrically bypassed.

4.1.3. Infrared Cameras and Corona Detection

Because hot spots are often an indication of anomaliesin components, infrared (IR) cameras have alreadybeen incorporated into electrical equipment mainte-nance practices. Putting an IR camera on the line,however, helps achieve better spatial resolution andobtain otherwise impossible camera angles. Ultravi-olet (UV) emissions due to the corona effect (or localdischarges) can be another symptom shown by some



Figure 15. Broken strand visible by IR detection (left) and UV emissions detected with bispectral imaging, emanating froman earlier version of LineScout (right).

defective components. Portable UV detectors, or bi-spectral imagers that superimpose a visible light im-age onto the UV image, could benefit from the cam-era angles provided by online teleoperated robots.Figure 15 gives examples of such images.

4.1.4. Audible Noise

Audible noise can focus the attention of mainte-nance personnel on a potentially defective compo-nent. Field work has shown that noise is a very nat-ural and intuitive means of detection. Microphoneswere thus included close to the inspection camera inthe LineScout Technology. It was also found that atwo-way audio system on the robot could facilitatecoordination with the linemen as the robot is beinginstalled on the line.

4.1.5. Specialized Visual Inspection

Certain types of line components require specializedvisual inspection. Warning spheres installed on theOGW are one example, because they hide a lengthof conductor, making it impossible to inspect visu-ally. Warning spheres are attached with clamps orpatch rods, which create an area of mechanical stressthat needs to be inspected. Because the mechanicalintegrity of the wire cannot be guaranteed, blindlysending linemen on a motorized trolley that runsalong the OGW raises some questions. One logicaloption is to send a robot to visually inspect the con-ductor prior to sending linemen. To do this, a minia-ture camera, possibly equipped with a light, mustbe inserted into the sphere through one of the drain

holes, as shown in Figure 16. Inserting the camerasfrom a cable subjected to wind-induced vibrationsrequires such dexterity that the job more closely re-sembles a maintenance task than a mere inspection.

4.2. Maintenance

Even though inspection tasks have a great potential,the longer term future of power line robotics couldreside in maintenance tasks, such as taking mea-surements, component replacement, and componentcleaning. To be able to perform such tasks, the mo-bile platform must be highly effective, use feedbackfrom a greater number of sensors, and have a certainnumber of autonomous subsystems, allowing the op-erator to focus on the maintenance task.

4.2.1. Conductor Repair Clampand Patch Rod Installation

Broken strands are common on OGWs, mainly dueto lightning strikes. In most cases, the damage cannotbe quantified reliably from the ground. The safest ap-proach is to send a robot to gather visual informationto assess the remaining mechanical strength. Hav-ing reached the damaged area, repairing the OGWor conductor would be the next logical step becausethe wind sometimes unravels the broken strand to apoint where the distance with the conductor is insuf-ficient and flashover occurs. A tool for temporary re-pair was designed for LineScout, allowing the teleop-erated installation of a custom-made clamp to secure



Figure 16. Mounted on the LineScout Technology, a minia-ture CCD camera and light are inserted for warning sphereinspection (artistic rendering showing the sphere being cutopen).

the broken strands around the wire (see Figure 17).This application is already in use, but tools to installpatch rods for permanent repair would be the ulti-mate solution.

4.2.2. Component Replacement or Installation

The potential for maintenance tasks has been demon-strated successfully in the installation of warningspheres by Ruaux (1995) and Campos et al. (2002).LineScout has the ability to remotely screw on and

unscrew different clamps because a rotating tool hasbeen fitted to the end effectors of its robotic arm(Figure 18). It was used recently to retrieve severalvibration dampers that became loose and made theirway down the slope of a span. This opens the wayto replacement and installation of vibration dampers,spacer-dampers, aerial markers, etc.

4.2.3. Component Cleaning

Contaminants of all kinds can be found on con-ductors installed in specific areas. Pollution residuesand vegetation are the most common contami-nants, although recurrent vandalism (kites, shoes,etc.) may also be a problem in some parts of theworld. In 1999, as reported by T&D (1999), a clean-ing device was designed by Hydro-Quebec IREQand implemented (10 units) in South America. Itproved its worth by cleaning 800 km of circuits(Fig. 19, left). Pulled from the ground with an insu-lated rope, this module, or a similar one, could even-tually be mounted on a mobile robot capable of cross-ing obstacles.

Contaminants (dust, vegetation, salt) on insu-lators can be a real problem for transmission gridowners. Because flashover could occur, the insula-tor string must be cleaned. As with any maintenancetask, it would preferable for this job to be carriedout on energized circuits. Today, live-line insulatorcleaning techniques involve shooting high-pressurede-ionized water or blasting with some type of pow-der. Some authors, such as Cho, Byun, Park, and Kim

Figure 17. LineScout introducing maintenance tasks such as the temporary repair of broken strands by installing a copperclamp (left) that is clamped around the conductor (right).



Figure 18. LineScout retrieving a loose vibration damper.

(2006), have introduced specialized robotic tools forinspecting and cleaning insulator strings, as shownin Figure 19, right. Power line inspection robots ca-pable of crossing obstacles could serve as a movingplatform to deploy such tools.

4.2.4. Conductor Replacement

The replacement of old conductors or OGWs can beperformed on live lines using the cradle-block string-ing method. Usually using simple traction machinesthat cannot cross obstacles, the method could bene-fit greatly from a traction machine capable of cross-ing obstacles. Pulling a safety line or a safety net witha robot that runs on an old conductor, possibly ob-structed by aerial markers or other obstacles, couldsecure an area prior to work by linemen.

4.2.5. Support Structure Painting

Deterioration by corrosion of steel lattices can be pre-vented by refurbishing the galvanized layer of thesteel support structure. Repainting the structure is anavenue, but live-line painting of the top of the sup-port does present a number of challenges for linemaintenance personnel.

5. DISCUSSION

Although much work has been achieved in recentyears, considerable developments still need to bedone before reliable, autonomous mobile robots willbe routinely performing inspection or maintenanceon transmission grids.

Over the past 10 years, the authors developedseveral robotic systems aiming at live-line trans-mission maintenance that were used extensively onHydro-Quebec’s transmission network. From thisbroad field of experience and based on key elementsof the state-of-the-art review presented herein, thefollowing conclusions are drawn for the future oftransmission line robotics:

• The best approach to locomotion, consideringpower consumption and speed of displace-ment, is rolling on the conductor.

• An average speed for traveling should bearound 1.0 m/s. Significantly lower speedwould limit the efficiency of the inspec-tion task; much higher speed is likely tobecome unsafe due to the possible pres-ence of unsuspected obstacles such as brokenstrands.

Figure 19. Contaminants being brushed off a conductor in South America and an insulator-cleaning robotic device de-signed by KEPRI (Cho et al., 2006; c©2006 IEEE).



• Obstacle-crossing time should not be over4 min, again for the efficiency of the inspec-tion task.

• Sufficient payload capacity, in the range of15–20 kg, should be aimed at for sensorsand other subsystems because the economicand strategic value of transmission robots re-sides in their capacity to achieve maintenancetasks.

• Based on the business case, access to singleconductors, bundled conductors, and groundwires is a must. Also, the device has to crossmost obstacles found on a typical line but notnecessarily on dead-end towers.

• Line maintenance robots can be teleoperatedbecause they are most commonly used forlimited jobs on few specific spans. It shouldbe intuitive and safe to operate such robots.Modularity is a key factor to accommodatevarious types of tools and sensors.

• The system must be reliable and safe (opera-tor safety, public safety, and line componentintegrity and service continuity). It must beadapted to live-line installation and operationmethods. For that reason, robot developersare encouraged to establish close collabora-tion with electric utilities.

• Robots have to be able to work on liveconductors up to 1,200 kV and withstandthe magnetic field associated with 2,000-Acurrent.

• The mobile platform design is the main chal-lenge, but application modules are the key tosuccessful inspection and maintenance tasks.Commercial sensors, typically used by line-men, should be used whenever possible asmodules to mount on robotic platforms.

• Line patrol robots traveling on the OGW onlyallow visual inspection of the conductors be-low, preventing the use of sensors that need tocontact the conductors and line components.Furthermore, this visual inspection is limitedin its quality and offers a single point of view.

• Line patrol robots that would run on ener-gized conductors would benefit from beingcompletely autonomous and having a batteryrecharging system that extends their auton-omy to several days.

• A promising field of research for power util-ities is line fault detection and identification.Sensors for that goal still need to be designed

and validated. Ultimately, the information ob-tained will be processed and component diag-nostics could be provided.

Figure 20 summarizes the interrelations thatshould ideally exist around developers of transmis-sion line robots. The overall driver of the processshould be electric utility needs that constitute the ac-tual business case of any project. These needs areemerging because utilities are being pressured byseveral factors, as indicated in Figure 20. This pres-sure, like the number of electric utilities involved, islikely to grow in the near future.

Some of the current needs in the areas of inspec-tion and maintenance were presented in the preced-ing sections. However, needs are constantly evolv-ing, and a close relationship with line maintenancepersonnel should be established and maintainedto refine the definition of needs. Also, as demon-strated by Section 3, many technical specificationswill be developed and clarified by the electric utilitiesthemselves.

Finally, partly because all these potential appli-cations represent a niche market, developers shouldmaintain close relations among themselves. This isparticularly true among platform design teams andamong companies that specialize in the developmentof commercial sensors.

6. CONCLUSION

A comprehensive state-of-the-art review on mobilerobots capable of crossing obstacles on transmissionlines was presented. As the amount of recently re-ported work indicates, this type of technology islikely to emerge and be deployed over the mediumterm.

Future work should mainly be oriented towardbattery technologies, getting power from live lines,100% reliable obstacle detection and identification,and sensor fusion to increase the autonomy level. Fu-ture transmission line robots must leverage progressachieved in other robotic fields such as planetaryrovers or autonomous vehicles: advanced control, ex-pert systems, advanced materials, image processing,localization and mapping, etc.

Power lines do need to be inspected and main-tained. Because this must be done on live compo-nents, the hazards it entails create a strategic en-vironment where robots are likely to make inroads



Figure 20. Transmission line robot development context.

and complement the available toolbox of line main-tenance personnel.

ACKNOWLEDGMENT

The development team would like to thank itsHydro-Quebec TransEnergie partners for their pre-cious collaboration in transmission line roboticsprojects.

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