Rebuilding Puerto Rico: Stringing Power Lines with Drones

Duke Energy, a public utility company, has a remarkable story about using drones to help in the rebuilding effort to restore power to Puerto Rico after last year’s hurricane. It’s likely the first time a drone has participated in actual construction, rather than just collecting photos and video of a project.

Duke Energy’s drone team in Puerto Rico


Duke Energy’s drone team was originally brought out to Puerto Rico to perform reconnaissance to assess damage to power transmission line and towers, and scout new access routes for work crews. This type of task is a great example of having drones tackle a dull, dirty, and dangerous job. However, the team quickly realized they could go beyond observing to participating directly in reconstruction effort itself by using the drone to run a guideline (thin rope normally used in parachute lines) between transmission towers. Work crews then attach the real power line to one end of the guideline and begin reeling it in to string the power line between towers.

One of the drones used by Duke Energy


Replacing a Dangerous Job with a Drone

In a city, where poles may be less than a block apart, there’s not much benefit to using a guide line, but as Duke Energy points out, in more remote areas the land between transmission towers can be impassable (like the rough terrain in Puerto Rico). To avoid bushwhacking from one tower to the next, crews use a guideline which is flown from one tower to the next. Previously, this has been done with helicopters that had to fly within fifty feet, or less, of the tower, or by firing the guideline from a shotgun, which had limited range. When your options are “thread a needle using a helicopter” or “fire a shotgun at it,” you’ve found dangerous job that’s begging to be performed by autonomous robots, like a drone.

So instead of using a helicopter to perform this dangerous (and expensive) task, Duke Energy’s team repurposed their drones to fly the guideline between towers. For the drone community, Duke Energy’s blog post is light on details, so we’ve dissected their photos, videos and blog post combined with past statements the company has given on their drone initiative to put together a more complete picture of what happened:

The Setup

Duke Energy is using a pretty hefty drone, with six (downward facing) rotors, that’s a configuration you rarely see these days. The guideline is attached with a magnet, so if the guideline become snagged, the drone could break free (much like the beloved MagSafe adapter on Macs). On the ground end of the guideline, the spool of rope was held by one of the crew, likely so they could carefully give the line just enough slack as the drone flew.

One of the real dangers of tethered drones, and why they’ve been difficult for to design, is that any tension on the tether quickly turns the drone from a free-flying robot into a high powered pendulum. The main challenge lies in keeping the tether just taut enough- too tight and the drone starts swinging around like a yoyo, too loose and your tether inevitably snags onto something. There’s also the problem of the drone becoming tangled in the tether itself as it spins around, or wind blows a slack line onto tree branches.

The Operation

The drone was flown manually by a pilot within Visual Line of Sight. There’s no mention of how many flights or guidelines were strung, but we do know the longest guideline was 1,200 ft and over 9,000 ft of line was used in total.

It’s safe to assume Duke Energy flew at least between ten and twenty guidelines, more than enough to demonstrate the feasibility of the project. Flying with a manual pilot was a smart choice, but must have been stressful as the tether began to affect the drone’s flight controls near the end of the flight.

Ten to twenty guidelines is interesting, but what if beyond-line-of-sight flights were allowed by the FAA? Would this number be closer to 80-90% of all the power lines strung in Puerto Rico?

The Regulations

The FAA’s Part 107 regulations specifically prohibit delivery, but precisely what constitutes a delivery is a murky topic when we stop thinking about packages as being cardboard boxes. One could argue that the guideline was being delivered to a tower, or that it was a tether that was conveniently detached part way through the operation.

Duke’s use case exemplifies why so many of the well-intended regulations from the FAA have often broken down in the real world. What if the drone had been used to fly the guideline up to a workman on the tower? Would that be a delivery? What if it had been a part to connect the transmission line to the tower?

What If a Utility Had Said This Instead?

Today we’re pleased to announce that in conjunction with our normal work crews, we were able to accelerate restoring all of power to Puerto, from the estimated six months to just three weeks. In the past, rebuilding the power line infrastructure in challenging terrain like Puerto Rico was slow, challenging and dangerous for our crews…

… Next hurricane season, we are planning to position construction drones at vulnerable power plants so they can immediately begin assessing damage after a storm and then start the rebuilding effort before our skilled workers are even onsite.

– A Near-Future Power Co.

What is the Next Dangerous Job Drones Will Help?

Will Duke expand the use of drones stringing power lines to their operations to the mainland US? Vox argues that it’s cheaper for utilities to repair rather than harden power lines for storms, and using drones will make that process even faster and cheaper than before.

Beyond stringing power lines, there are several other types of dangerous jobs that we believe drones could be used for:

  • Inspecting earthquake damage
  • Shingling roofs
  • Fighting fires
  • Installing and repairing equipment on tall structures

Any dangerous job will take advantage of drones’ greatest strength: that they are a platform for moving a payload, be it a camera, a firehose, or a parcel, anywhere that is difficult for humans to reach on their own.