PowerDonut: Four Decades of Innovation in Overhead Line Monitoring
How the Power Donut became a trusted overhead line monitor, and the inventions behind four decades of Dynamic Line Rating.
Some technologies stay around because they solve a problem that never goes away. The PowerDonut® is one of them. Clamped directly onto a live conductor, it has been telling utilities what their overhead lines are really doing since the 1980's, and is still the foundation of how Atecnum approaches Dynamic Line Rating (DLR) today.
A short history
The PowerDonut® began in the 1980´s at Niagara Mohawk, now part of National Grid, as one of the earliest devices for real-time overhead transmission line monitoring. Underground Systems, Inc. (USi) later took it forward and developed it further. Today the PowerDonut® is owned by Atecnum Corporation and manufactured in the U.S.A.
Along the way, the engineers behind it kept inventing. New ideas about how to power a sensor on a live wire, how to communicate data, and how to turn a few measurements into a trustworthy picture of transmission line variables. Many of these ideas were captured in patents. When Atecnum acquired the PowerDonut® business, it acquired that body of intellectual property as a valuable asset that stands today.
Over the years, protection for these inventions was sought in the United States and in many other countries, including Canada, much of Europe, China, South Korea, etc…
Relevant patented innovations
Some of Atecnum's active patents that make the PowerDonut® unique cover the following innovations:
Working out sag and temperature from simple measurements.
(U.S. patent 7,641,387). A line sags as it heats up, and utilities need to keep it clear of the ground. The PowerDonut® covers a way to estimate the average temperature and sag of a whole span from a single temperature reading plus a measure of how the conductor is tilted or how tightly it is pulled.
Powering and connecting a sensor on a live line.
(U.S. patent 8,497,781). How a line-mounted device chooses between its battery and the power it draws from the line itself depending on how much current is flowing, and how several devices on a line can pass their data along a chain to a ground-based system.
A battery-powered monitor that wakes up when the line moves. (U.S. patent 9,069,018). A transmission line monitor that rests in a very low-power state and wakes up to measure when it detects the vibration of the conductor, then passes its status on to the next monitor in the chain. It was designed for places such as railway catenary lines and DC lines.
Earlier innovations that have made the PowerDonut unique
Not every patent stays in force forever, and some of the PowerDonut® important ideas have completed their term, although once expired the patents can cover past infringements for up to six years depending on the country of issue. Some of these follow:
A sensor you can mount on a live line. (U.S. patents 7,733,094 and RE44,256). The original platform patent describes a donut-shaped housing on two hinged halves that clamps around an energized conductor, with no outage needed. Inside, it measures current, voltage, temperature, inclination and vibration, records what it sees, and draws its power from the line with a battery as backup. It can also report where a fault occurred from measurements taken at one end of the line. This family ran its full term, to October 2025 abroad and April 2026 in the United States.
Dynamic Line Rating that keeps up as a line ages. (U.S. patent 7,504,819). Conductors slowly stretch over the years, a process called creep. This patent turned the sensor's inclination and temperature readings into the span's sag and tracked creep over time, so the line rating stayed valid as the line aged. It is also the patent that names the PowerDonut® as its preferred sensor.
The first line-mounted measurements. Earlier patent families covered measuring line potential from a sensor on the conductor, calculating the Fourier components of power line signals, and a monitoring system for lines and substations.
The PowerDonut today
Today the PowerDonut® PD4 carries that heritage into modern Dynamic Line Rating (DLR) and Grid-Enhancing Technologies (GETs). It is the clamp-on overhead line monitor utilities use to measure temperature, sag and current on live lines, working alongside weather stations and the PDS20 software. Its newest inventions, the ones covered above, are what keep it current. Atecnum’s current patents and those recently expired are valuable assets belonging to Atecnum Corporation.
Atecnum Corporation, Boynton Beach, Florida, U.S.A.
