Robotic Tightrope Walkers for High-Voltage Lines
Inspection bots in Canada and Japan roll out to make power lines safe
INSPECTOR GADGET: HiBot's Expliner robot examines active high-voltage power lines by rolling along the upper cables in a bundle of four [left]. A counterweight hangs below, while a sensor arm is deployed in front of the pulleys to inspect the lines [right].
This story was corrected on 16 November.
12 November 2009—High-voltage power-line inspection has always been a dangerous job for humans, so a handful of companies are sending in the robots. One such company, the Tokyo-based HiBot, is working with western Japan's Kansai Electric Power Co. to field a new robot next year that can inspect several power cables at once, a first for such daredevil bots.
As power-transmission lines age, preventive maintenance and inspection become more important. Many lines in western Japan are 80 years old, says Michele Guarnieri, a HiBot cofounder and technical consultant for the company. Recent power blackouts in Canada and the United States have also highlighted the need to ensure the power grid's stability.
Transmission-line inspection is currently the domain of humans who walk high on the lines like tightrope walkers, which means that the power lines have to be turned off before inspection can begin. That's a drag for electric companies, which have to reroute power through parallel lines or cut off service altogether for the duration of the inspection. Especially as energy demands increase, says Serge Montambault of Canada's Hydro-Québec Research Institute, it's becoming more difficult and costly to "get a line out of the network"—hence the search for a robotic alternative that can inspect live power lines.
HiBot's inspection robot, called Expliner, proposes to do just that. It's designed to roll along a typical high-voltage "bundle" in Japan: a set of four cables held in place by half-meter-wide square-shaped spacers every 30 meters or so. Expliner has been successfully tested on live wires up to 500 kilovolts, the maximum voltage pulsing through Japanese transmission lines, according to engineer Paulo Debenest, another HiBot cofounder. The robot is like a four-wheeled cable car that rolls along the upper pair of bundled cables. From one side of the robot dangles a manipulator arm, which also serves as a counterweight for balance.
A big challenge for transmission-line robots is crossing obstacles that crop up on the line. Some obstacles, such as the cable spacers that keep bundled lines in place, are relatively easy to roll right over. Others, such as suspension clamps that hold up the line, block the way. Expliner gets around such things by using the dangling counterweight to shift the robot's center of gravity, which in turn raises the wheels on the front and back axles up and out of the way of obstacles.
For example, if the robot is approaching a suspension clamp, which we might think of as a post sticking up in the road, the robot shifts its weight to lift its front axle off the cables, then an automated process rotates the axle out of the way, like pushing open a gate. The robot advances until the axle passes the obstacle, and then it pulls the axle back to the cables. It then does the same routine for the back axle.
If the obstacle is more difficult, such as a steep incline in a mountainous region or a tower affixed to the line with more than a single simple insulator, the robot would have to be brought down and installed on the other side of the obstacle.
But navigation along the lines isn't the only goal. The robot must also do a good job of inspecting the cables. For this, Expliner uses four sets of sensors—one set for each of the four cables in a bundle, each including laser sensors for greater sensitivity—which give the robot the ability to see the whole surface of each cable, to spot corrosion or scratches, and to discern tiny changes in cable diameter that could indicate damage inside the cable, such as a broken steel strand.
In addition to the laser sensors, Expliner has a high-definition, high-zoom camera that can record the details of bolts and spacers up close far more effectively than a helicopter or even a person, says HiBot's Debenest.
IN THE CLEAR: Hydro-Québec's LineScout approaches a suspension clamp obstacle. The Canadian robot is designed to roll over a single high-voltage line, with gripper arms that allow it to cross obstacles like the clamp.
HiBot and Kansai plan to have their robot in operation by March of next year, according to Guarnieri. In two years, says Kansai's Expliner project manager, Kiyoshi Tamura, "we plan to have trained workers operating these robots to conduct practical inspection tasks."
At that point, Expliner will double the total number of transmission-line inspection robots in service. Hydro-Québec's LineScout—a single-line roller with gripper arms that grasp each side of an obstacle and flip the traction wheels from one side of an obstacle to the other—is the only such bot in operation on live power networks now.
According to Montambault, of Hydro-Québec, this robot has done six jobs on Quebec's power lines since 2006, including actual manipulation of line components last year. In a review of the state of the art in transmission-line robotics published earlier this year, Montambault and his colleagues suggested that such maintenance—not just inspection jobs—will become an important application of robotics for the power industry.
"It's one thing to run on a live wire," Montambault says. "But [robots] need sensors and tools to add value to every presence [they] have on the network." His goal is to fully automate the LineScout device. However, the transmission-line maintenance field is "quite a conservative place, so just using robots is something," he says, and there will "still be a human in the loop for many years to come."
HiBot's Expliner is not aiming for autonomy, according to Debenest. In the field, he says, line technicians are "happy to have a machine that makes their job easier, safer, and more efficient, of course, but they want to be in charge of the machine." Guarnieri adds that keeping the bot teleoperated makes the system "simpler and cheaper," a must for electric power companies.