Keeping an Eye on the Grid

For many years, robotic technologies have proven, in many sectors of activities, to be a valuable means of inspecting and performing in-situ maintenance operations on equipment and structures. Recently, robotic devices have broadened their reach to the electric industry as major utilities around the world are in the process of introducing robotics into their operation and maintenance practices. The main drivers for this trend are worker safety, operational efficiency, system reliability and the availability of equipment.

The traditional methods electric utilities use to gather information on the condition of their overhead line components include tower climbing, insulated boom trucks, line patrols with all-terrain vehicles, and linemen traveling on motorized trolleys or conductor carts. Full-scale helicopters and fixed-wing aircraft also are part of utilities' tools and methods to inspect and assess their systems.

New developments are under consideration with mobile robots such as unmanned aerial vehicles, fixed-wing or vertical takeoff and landing, unmanned ground vehicles, robots rolling on conductors and teleoperated boom trucks. Satellite imaging also could be considered a promising avenue for grid operators. All of these approaches have to be regarded as complementary.

When comparing the benefits of these alternative solutions, the utility must consider many factors:

Precision, type, quality and amount of data gathered
Nature of the data (quantitative vs. qualitative)
Capacity to process and use the data
Length of overhead line inspected or maintained per day
Possibility of working on energized lines
Capacity to achieve in-contact measurement
Capacity to repair or replace components
Acquisition, implementation, operational and maintenance costs
Expertise, training and technical staff required to operate and maintain the technology or method
Deployment complexity
Applicable regulations
Existing working methods and procedures
Risk management practices
Operational context
Grid configuration.

Because of all these factors, it is not trivial to positively qualify a tool or method as better than another one, and it would be a mistake to think there is only one method to determine condition assessment. Continual improvements are being made, as demonstrated by the LineScout technology developed and used by Hydro-Québec.

Design of the Robot

The robot also had to be designed in an open-architecture philosophy, meaning the mechanics, electronics and software had to accommodate the introduction of new features and sensors that were to be implemented over the years, such as a robotic arm equipped with several tools and sensors.

Onboard cameras have two important roles: providing a visual feedback to the operator (the most important feedback for remote operation) and the principal, most intuitive means of inspection. LineScout is equipped with up to four zoom cameras mounted on programmable orientation mechanisms. These programmable pan-and-tilt units automatically provide the relevant points of view as an operator addresses the crossing of an obstacle. It allows the operator to focus mainly on inspecting line components and less on controlling the robot.

Other forms of feedback were found to be important to the operator: audible sound, pitch and roll values from inclinometers, the battery charge level, the internal temperature of some key systems and a virtual 3-D model of the robot that shows the exact configuration of the robot in real time. At any time, the operator can access configuration panels of most peripheral systems (sensors, tools, feedback devices). GPS coordinates and odometer readings also provide important information for inspection reports to complement the grid operator's existing database.

A modular robotic arm implemented on the mobile platform can reach all conductors in a bundle. Also, it serves as a base for the quick-connect mounting of various tools and sensors, allowing for the following tasks:

Visually inspect conductors (360 degrees) and line components such as spacer dampers on a bundle of conductors
Measure the electrical resistance of splices
Install aluminum clips to temporarily repair broken strands
Tighten or loosen bolted line components
Perform infrared imaging.

Another important task LineScout can accomplish is related to the high traction force of the mobile platform: overhead ground wire and conductor replacement using the cradle-block stringing method. This method can be extremely valuable for crossing spans over highways, railways and water, and when performing a live-line task. It also allows use of the conductor being replaced as a support to eventually string the new conductor.

Field-Orientated Design

LineScout technology is probably the only conductor inspection robot in use on transmission systems in the world, and since 2006, it has been used on energized conductors. It deals with existing structures and line components, is able to cope with existing live-line working methods and is targeted to high-value applications identified by Hydro-Québec TransÉnergie maintenance personnel. Its reliability has been proven over the years, and the strategic choices made regarding its technical specifications led to the value and field adaptability of the technology seen today.

Furthermore, it is believed the following considerations were significant in achieving a successful and straightforward transition from the laboratory facilities to Hydro-Québec's transmission system:

Working on an energized line: As opposed to focusing strictly on overhead ground wires or de-energized conductors, energized lines are where the real value stands.
Designing the robot in accordance with existing live-line working methods (installation and retrieval) and standard hot-line equipment: This illustrates how important it was to involve the end users throughout all stages of development.
Dealing with existing structures and line components: Retrofitting existing towers and line components to suit robotics inspection is not an option for most utilities. Adapting new line design to suit robotic maintenance may be a good idea, but the benefits would not accrue for many years.
Covering the transmission system: Providing access to ground wires, single conductors and bundles of conductors enlarged the scope of LineScout's possibilities.
Covering exceptional situations: As experienced over the last years, challenging circuits were among the most valuable field of operations for LineScout. This has been made possible by being able to cross a wide variety of obstacles and sequences of obstacles; having access to horizontal and vertical circuit configurations; and being able to operate on very long and steep spans, angle towers and damaged line components.
Rigorous design: Robustness, safety of operation and reliability of systems is paramount.
Aiming at high-value applications and features: The added value of such a drastic change in maintenance practices must be significant and obvious to asset managers.

In addition to electromagnetic fields, the technology has to operate under harsh conditions: mechanical shocks (during transportation and installation), dust, water (and snow), a wide range of ambient temperatures, aeolian vibrations (when attached to the conductor) and ground transportation.

The involvement of end users in the design process is a major factor in maximizing the chances a technology will be technically suitable for field deployment. Also, technology acceptance will be greatly influenced by apparently simple yet very important details and features related to handling, installing and operating the technology.

At BC Hydro and Hydro-Québec, a few water crossings inspections using LineScout technology were initiated in 2009. In 2010, a total of 16 large-scale inspections were planned and undertaken on the transmission systems of both utilities. The main aim for each inspection was to gather visual information on conductors (single and bundled), ground wires, structures and line components, looking for possible defects or signs of wear. Each of these inspections was performed in a challenging environment on spans as long as 1.3 miles (2.1 km), between towers up to 500 ft (152 m) high, with challenging access conditions and on conductors with slopes of more than 30 degrees.

At least 15 different variations of the basic installation method have been developed to suit different circuit configurations, towers and landscape. So far, more than 10 different line crews have been involved in successful LineScout field deployments. As LineScout is used by more and more crews, new potential applications are discussed and the area where the technology has an impact is increasing.

Helicopter-based installation and retrieval methods were developed and validated in 2011. These methods open up new possibilities in reaching remote circuits or otherwise difficult-to-access spans.

Impact and Benefits

Early assumptions on the potential value of a mobile robot capable of inspecting live power lines were based on new live-line work possibilities and on the capability of such a technology to allow gathering high-value data on the condition of the system. As the project was defined and the business case examined more closely, it became obvious significant economic and strategic impacts would come from a successfully implemented transmission line inspection robot.

Having improved condition assessment tools, access to quantitative data and state-of-the-art inspection technologies impact several elements:

System sustainability by optimizing investment planning as aging assets approach their end of life (project prioritization and refurbish or replace decisions)
System reliability and risk management through optimal assessment of power lines
Inspection efficiency by providing exceptional points of view for visual inspection, measurement capabilities (quantitative data), complete and rigorous assessment of the line, and real-time sharing of inspection data with experts on the ground
Data archiving by populating grid owner databases and allowing follow-up on condition assessment.

The LineScout should be regarded as providing a versatile mobile platform that allows access to energized circuits, challenging spans and hard-to-reach line components, resulting in several benefits:

System availability by allowing live-line inspection and maintenance tasks in some situations where no other means is available
Worker safety by allowing remote access in such potentially hazardous working environments, such as energized lines, damaged conductors and spans with very steep slopes
Access to hard-to-reach spans and line components, such as over water, roads, and railways, in mountainous regions, across farmland during crop season and in urban areas.

Recognition of Success

As LineScout technology has been successfully deployed on transmission systems since 2006, it demonstrates some key and strategic decisions were made early in the development project. Technical specifications that guided the design of the robot were determinant, focusing on important aspects directly related to end users.

The business case behind LineScout features, implemented applications and targeted tasks were of particular importance in that success. Additionally, a good knowledge and understanding of the extremely challenging operational conditions under which the technology was to be operated had a great influence on system complexity, robustness and reliability. Early involvement of end users in the development was surely crucial and essential.

Robustness and suitability to field conditions of the LineScout were clearly confirmed with more than 50 field deployments. This year, an additional three new units of LineScout were manufactured, increasing to five the number of complete robot units available for deployment.

The Edison Electric Institute named British Columbia Transmission Corp. (now BC Hydro) and Hydro-Québec joint winners of the 2010 Edison Award, the electric utility industry's highest honor, recognizing outstanding leadership innovation and exceptional contributions to the American and international industries. Since 2008, both utilities have been collaborating in the implementation of LineScout technology in transmission line maintenance practices. The global electricity industry's major players clearly see robotics as a promising field of solutions to help grid operators meet their existing and future operational challenges.

Acknowledgement

The development team would like to thank its Hydro-Québec TransÉnergie partners for their precious and essential collaboration in transmission line robotics projects.

Serge Montambault ([email protected]) is a mechanical engineer with a Ph.D. degree in robotics from Université Laval. He joined the robotics and civil engineering department of Hydro-Québec's Research Institute in 1997 and has since been heading projects for the development of robots applied to the inspection and maintenance of power industry systems and equipment. He and his team have won two Canadian engineering awards as well as the 2010 Edison Award from the Edison Electrical Institute.

Nicolas Pouliot ([email protected]) is a mechanical engineer with a master's degree in robotics and mechanism design from Université Laval and University of Victoria, respectively. Since January 2002, he has worked as a researcher in the robotics and civil engineering department of Hydro-Québec's Research Institute. He has been in charge of the technical development, testing and field deployment of robotic systems dedicated to power line inspection and maintenance, including the LineScout robot.

LineScout Technology

LineScout Technology, developed at Hydro-Québec's Research Institute, is a robot used on power lines, rolling on the phase conductor, ground wire or one of the lower-phase conductors of a bundle. As it reaches an obstacle such as an insulator string, a spacer damper or a conductor warning sphere, it is able to go around the obstacle. A set of arms and grippers offer a temporary grasp on both sides of the obstacle, allowing wheels to disengage and flip down underneath the conductor prior to crossing to the other side. This 2-minute operation is teleoperated from the ground.

Early design specifications of the robot were developed in collaboration with the end users from Hydro-Québec TransÉnergie field personnel. Decisions on which obstacles should be crossed were based on three factors: frequency of occurrence of such an obstacle on the grid; impact of the capacity to cross that particular obstacle on the value of inspections; and its impact on the overall design in terms of added complexity, weight, compactness, robustness and reliability. Therefore, at the beginning of the project, the most important factors were taken into consideration:

Capacity to be used on 735-kV, 1,000-A transmission live lines
Able to access the ground wire, a single conductor or one of the lower conductors of a bundled configuration (double, triple, quad or more)
Cross an obstacle of a maximum length of 30 inches (76 cm), a typical warning sphere
Cross a series of adjacent obstacles
Cross obstacles in less than 2 minutes
Climb a 30-degree slope, such as those encountered on a large crossing
Negotiate 12-degree horizontal turns at suspension towers
Accommodate most conductor and splice gauges without any modification to the platform
Roll at an average speed of 2 mph (3.2 kmph)
Weigh a maximum of 250 lb (113 kg), including tools and sensors
Capacity to operate the robot from a distance of 2.5 miles (4 km)
Able to employ existing live-working methods and tools, and have a 20-minute typical installation time once positioned at the tower
Control mode is teleoperational so an operator remains in the loop
Safe, reliable and intuitive operation from the ground
Cope with real-world field operation context, including the following:
- Work safely in winds of up to 25 mph (40 kmph)
- Tolerate light rain
- Operate at temperatures of 5°F to 85°F (-15°C to 29°C)
- Battery autonomy sufficient to sustain a full day of work.