Inga Stefánsdóttir
Sep 10, 2025
When power lines cross wide, open landscapes, they face winds that can pose unique challenges. One striking example is a fjord-crossing span in Iceland. Stretching 480 meters across open water, the line is fully exposed to steady crosswinds. In early March 2025, after an LKX-MULTI device was installed on the span, it began capturing unusual oscillations almost daily, far more frequent than on other lines. What was happening? In short: aeolian vibration, a wind-induced conductor vibration that can silently damage power lines over time.
What Is Aeolian Vibration and Why Does It Matter?
Aeolian vibration is a high-frequency, low-amplitude oscillation of overhead conductors caused by steady winds blowing perpendicular to the line. As wind flows past the cylindrical conductor, it forms alternating vortices on the downwind side, a phenomenon known as vortex shedding. If the wind speed is in the right range (typically about 1–7 m/s), these alternating vortices create rhythmic forces that make the line vibrate like a guitar string.
While the motion is small, the consequences can be serious. Aeolian vibration repetitively flexes the conductor and its hardware, causing cumulative fatigue damage. Over time, this can lead to broken strands in the conductor or damage to fittings like clamps and insulators. The risk is greatest near tower attachments, where bending stresses concentrate. In extreme cases, uncontrolled vibration can lead to catastrophic line failure. For both reliability and safety, it’s critical to recognize and mitigate aeolian vibration on susceptible spans.
A video captured by the LKX-MULTI device at the span, shows exactly how this looks in practice: the conductor moving in quick, subtle oscillations under steady fjord winds.
A view of the fjord crossing span. Its unique exposure to steady perpendicular winds makes it a hotbed for aeolian vibration.
A “Perfect Storm” of Wind Conditions at the span
What makes the fjord crossing span so prone to aeolian vibration? The answer lies in its unique location and wind environment. This span crosses a fjord with little to block or disrupt the wind. Importantly, the prevailing winds in the area blow almost directly perpendicular to the line an ideal scenario for vortex shedding. Moreover, winds at this site are frequently in the moderate range that triggers aeolian vibration. From March to September 2025, the average wind speed at the span was about 4.2 m/s, and nearly 90% of the time the wind stayed below 7 m/s. In other words, most hours were spent in the “aeolian danger zone” of steady, moderate breeze.
Wind rose chart for the span (March–September 2025). It shows that winds came predominantly from the east, southeast, and west, directions almost perfectly perpendicular to the conductor’s orientation (indicated by the blue line). The vast majority of wind speeds were in the lower to moderate range, typically between 1–7 m/s, which is exactly the range most likely to trigger aeolian vibration.
The span’s physical characteristics also play a role. At 480 m in length, it has a relatively low natural frequency and less inherent damping. It is strung with an ACAR (Aluminum Conductor Alloy Reinforced) conductor, 28.14 mm in diameter, a strong cable, but one that, like any conductor, can vibrate under the right conditions. The fjord likely channels winds in a stable, laminar pattern, further fueling continuous vortex shedding. In contrast, gusty or turbulent winds tend to disrupt vibration. Here, the fjord acts almost like a wind tunnel, creating the perfect storm for sustained aeolian vibrations.
402 Hours of Vibration: What the Monitoring Revealed
Once Laki Power’s LKX-MULTI monitoring device was installed, the data quickly confirmed the issue. Over a four-month period (3 March to 7 September 2025), the span experienced an accumulated 402 hours of aeolian vibration, the equivalent of more than 16 full days of oscillation. These weren’t isolated events; vibrations occurred almost daily, often lasting for hours, unlike other spans equipped with the same sensors.
The system defined an “aeolian vibration event” by three criteria: (1) the conductor’s pitch fluctuations exceeded a threshold, (2) wind speed was in the 1–7 m/s range, and (3) wind direction was roughly perpendicular to the line. During the study period, all three conditions were met frequently, confirming that the span was undergoing persistent, classic aeolian vibrations under fjord-crossing winds.
Cumulative hours of aeolian vibration recorded per week on the span (March–September 2025). By beginning of September, the total reached ~402hours. This consistent activity was not seen on other monitored lines.
Local, on-site measurements were essential. A distant weather station would never have captured how often the fjord winds blow at just the right speed and angle to drive vibration. The case highlights the importance of measuring wind directly at the span in question, as terrain and orientation can make conditions uniquely risky.
Mitigation and Monitoring: Keeping Vibration Under Control
To guard power lines against aeolian vibration, operators usually turn to two key approaches: installing hardware and keeping a close eye through monitoring.
Install Vibration Dampers
The most widely used method is the installation of Stockbridge dampers, the weighted devices often seen near tower attachments. These are tuned to absorb the energy of aeolian vibration and dissipate it as heat. On long spans, several dampers may be installed at each end, providing a reliable first line of defense. This simple, proven technology has been used for decades and remains the go-to solution worldwide.
Continue Monitoring
While dampers control the motion mechanically, ongoing monitoring ensures the problem remains under control. Sensors track how often and how strongly a span vibrates, helping operators confirm that mitigation is working and giving them early warnings if risk levels rise again.
In short, the formula is straightforward: catch it, damp it, and keep watching it. With well-placed dampers and continuous monitoring, even wind-exposed fjord crossings can be kept safe from long-term vibration damage.
Who Should Pay Attention
Persistent aeolian vibration represents a progressive reliability risk. It rarely causes sudden failures, rather, it develops slowly, demanding ongoing monitoring, preventive maintenance, and timely action across multiple areas of utility operations.
Asset managers are responsible for long-term network reliability and cost control. Because vibration fatigue builds up quietly, neglect can result in costly repairs or unexpected outages.
Maintenance and inspection crews are often the first to notice early warning signs such as strand breakage, clamp wear, or hardware fatigue. Their on-the-ground observations are essential for early intervention.
Design and planning engineers must consider vibration exposure during span design, damper placement, and hardware selection to reduce risks before a line is built.
Operations teams play a crucial role in day-to-day system resilience, ensuring that mitigation measures such as dampers and sensors continue to perform effectively over time.
Broader Implications for Other Long Spans
The experience at this Icelandic fjord crossing offers lessons for the broader power industry. Many transmission lines have long spans over valleys, rivers, or fjords where winds are funneled into steady, perpendicular flows. These spans, while impressive feats of engineering, may also be quietly fighting the wind every day.
Operators elsewhere should take note: if a span is exposed to steady crosswinds, especially in the 1–7 m/s range, it may be vulnerable to the same kind of persistent vibration. A targeted monitoring campaign and the installation of dampers where needed can prevent fatigue before it accumulates. With modern sensor technology, early detection is easier than ever, allowing utilities to act before small vibrations become major problems.