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.