⚡ electrical engineering

Impact of Inhomogeneous Ice Accretion on Conductor Aerodynamic Stability

This study utilizes numerical simulations of crescent-shaped ice accretion to demonstrate that increased ice nonuniformity exacerbates conductor aerodynamic instability by widening the range of wind attack angles susceptible to galloping, thereby providing a theoretical basis for mitigating ice-related power grid disasters.

Original authors: Yang Feng, Zhengkang Li, Qin Xiao, Ji Kai, Fu Yucheng

Published 2026-07-03

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Yang Feng, Zhengkang Li, Qin Xiao, Ji Kai, Fu Yucheng

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Big Picture: Why Ice on Power Lines is a Wobbly Problem

Imagine a high-voltage power line stretching across a snowy mountain. When ice forms on it, it doesn't always look like a perfect, smooth donut. Sometimes, the ice builds up unevenly, creating a lopsided, crescent shape (like a half-eaten cookie or a banana).

This paper is about why that uneven shape is dangerous. When the wind blows on this lopsided ice, the wire doesn't just sit there; it starts to dance violently. This violent shaking is called "galloping." If it gets bad enough, the wire can snap, or the tower holding it up can collapse, causing blackouts.

The researchers wanted to figure out exactly how the unevenness of the ice makes this shaking worse.

The "Recipe" for the Experiment

To study this without waiting for a real blizzard, the team built a digital simulation (a computer model) of a power line covered in ice.

The Shape: They focused on "crescent-shaped" ice, which is the most common type that causes trouble.
The Variable: They created different versions of this ice. Some were thick, some were thin. Some covered the whole wire evenly (180 degrees), while others covered only a small slice (90 degrees).
The "Non-Uniformity Coefficient": This is the paper's main invention. Think of it as a "Lopsidedness Score."
- A score of 0 means the ice is perfectly round (no problem).
- A high score means the ice is very uneven and lopsided (big problem).
- They calculated this score based on how thick the ice was compared to the wire's size and how wide the ice arc was.

The Wind Tunnel (Virtual)

They ran their computer model through a virtual wind tunnel, blowing wind at the iced wires from every possible angle (0 to 180 degrees). They measured three things:

Lift: Does the wind try to push the wire up?
Drag: Does the wind try to push the wire backward?
Twist: Does the wind try to spin the wire?

The Two "Bad Guys" (Instability Mechanisms)

The paper uses two scientific rules to decide if the wire will start galloping. Let's call them the Up-Down Shaker and the Twister.

The Up-Down Shaker (Den Hartog Mechanism):
- The Analogy: Imagine pushing a child on a swing. If you push exactly when they are coming toward you, they go higher. If the wind pushes the wire in a way that adds energy instead of slowing it down, the wire starts bouncing up and down uncontrollably.
- The Rule: If the wind creates a "negative slope" in how it pushes the wire, the wire becomes unstable and starts galloping vertically.
The Twister (Nigol Mechanism):
- The Analogy: Imagine holding a long stick and twisting your wrist. If the wind catches the lopsided ice just right, it can make the wire spin or twist violently.
- The Rule: If the wind creates a torque (twisting force) that increases as the wire twists, it becomes unstable.

What They Found: The "Lopsidedness" Danger Zone

The researchers compared wires with low "Lopsidedness Scores" (more even ice) against wires with high scores (very uneven ice). Here is what happened:

1. The More Lopsided, The More Dangerous (For Up-Down Shaking)

The Finding: As the "Lopsidedness Score" went up, the range of wind angles that caused the wire to shake violently got much wider.
The Analogy: Imagine a perfectly round balloon. It's hard to make it wobble in the wind. Now, imagine that same balloon with a heavy rock glued to one side. Suddenly, even a gentle breeze from almost any direction can make it wobble wildly.
The Result: A wire with very uneven ice is unstable in a much wider range of wind directions than a wire with even ice. The "danger zone" for wind angles grew significantly.

2. The Twist Didn't Change Much

The Finding: The "Twister" instability (Nigol mechanism) didn't care much about how lopsided the ice was. Whether the ice was slightly uneven or very uneven, the range of wind angles that caused twisting stayed roughly the same.
The Analogy: The twisting problem is like a specific key that only fits one specific lock. Changing the shape of the ice didn't change the lock; it just made the shaking (wobbling) worse.

3. Bigger Wires = Bigger Danger

The Finding: Thicker wires (larger diameter) had a wider range of dangerous wind angles than thinner wires, especially when the ice was thick.

The Bottom Line

The paper concludes that uneven ice is the real culprit behind dangerous power line shaking.

If ice forms evenly, the wire is relatively stable.
If ice forms unevenly (high "non-uniformity coefficient"), the wire becomes unstable in a much wider variety of wind conditions.

Why does this matter?
The researchers say that by understanding this "Lopsidedness Score," engineers can better predict when a power line is about to start galloping. This helps them warn about potential disasters before the wires snap or the towers fall, keeping the lights on during winter storms.

(Note: The paper focuses strictly on the physics of the ice and wind interaction. It does not propose specific new hardware to fix the wires or clinical applications for human health.)

Technical Summary: Impact of Inhomogeneous Ice Accretion on Conductor Aerodynamic Stability

Problem Statement
The stable operation of transmission lines is critical for national socio-economic development, yet expanding power grids increasingly traverse complex terrains prone to extreme weather. Ice-induced galloping remains a severe threat, capable of causing conductor fractures, tower collapses, and phase-to-phase flashovers. While existing literature extensively investigates aerodynamic characteristics regarding environmental factors (wind speed, turbulence), icing parameters (thickness, roughness), and conductor configurations (bundle arrangements), there is a notable gap in research concerning the non-uniformity of ice accretion shapes. Since galloping instability typically occurs under non-uniform icing conditions, understanding how the distribution asymmetry of ice affects aerodynamic stability is essential for accurate risk assessment.

Methodology
This study employs a numerical simulation approach to investigate the aerodynamic stability of conductors under varying degrees of ice non-uniformity.

Numerical Model: The research utilizes the SST k-ω turbulence model, selected for its ability to accurately resolve both the main flow field and the near-wall region, which is critical for simulating wake fields around iced conductors. The governing continuity and momentum equations, along with transport equations for turbulent kinetic energy ( $k$ ) and specific dissipation rate ( $\omega$ ), are solved.
Mesh Strategy: An overset mesh method is implemented to efficiently capture aerodynamic parameters across various angles of attack. The domain is divided into a background mesh and a refined foreground mesh (covering the conductor and a 5D radius), connected via interface boundaries.
Simulation Parameters: Crescent-shaped ice accretion is modeled as the research subject. Simulations cover wind attack angles from 0° to 180° (exploiting symmetry) with 15° intervals. The study varies conductor diameters (20 mm and 30 mm), ice thicknesses (30% and 60% of diameter), and icing angles (90°, 120°, 150°, 180°).
Stability Criteria: Aerodynamic stability is evaluated using two established mechanisms:
1. Den Hartog Mechanism: Assesses vertical galloping stability based on the condition $C_D + \frac{\partial C_L}{\partial \alpha} < 0$ .
2. Nigol Mechanism: Assesses torsional galloping stability based on the condition $\frac{\partial C_M}{\partial \alpha} < 0$ .
Non-uniformity Coefficient: A specific parameter, the ice non-uniformity coefficient ( $a$ ), is defined as $a = (b/\gamma) \times 100\%$ , where $b$ is the ratio of ice thickness to conductor diameter and $\gamma$ is the icing angle. This coefficient quantifies the degree of ice distribution asymmetry.
Validation: The simulation model is validated against experimental data from Reference [17] (conductor diameter 26.82 mm, ice thickness 6.7 mm, wind speed 10 m/s). The simulation results for drag, lift, and moment coefficients show high consistency with experimental trends, confirming the model's reliability.

Key Results
The numerical analysis yields several specific findings regarding the relationship between ice non-uniformity and aerodynamic stability:

Aerodynamic Coefficients: As the icing angle decreases (increasing non-uniformity), the variation range of the lift coefficient increases significantly. The drag coefficient generally increases with ice thickness, while the torsional coefficient shows a slight increase in variation as icing angles decrease and thickness increases.
Den Hartog Instability: The study finds a direct correlation between the ice non-uniformity coefficient and the range of wind attack angles susceptible to Den Hartog galloping.
- For a 20 mm conductor with 0.3D ice thickness, increasing the non-uniformity coefficient widened the unstable wind angle range from 0° to 3°.
- For the same conductor with 0.6D ice thickness, the range widened from 1° to 6°.
- For a 30 mm conductor, the effect was more pronounced: at 0.3D thickness, the range expanded from 4° to 19°; at 0.6D thickness, it expanded from 5° to 21°.
- Conclusion: A higher non-uniformity coefficient widens the range of wind attack angles susceptible to vertical galloping, thereby exacerbating aerodynamic instability. Larger conductor diameters also correlate with a larger range of Den Hartog galloping angles.
Nigol Instability: In contrast to the Den Hartog mechanism, the range of wind attack angles susceptible to Nigol (torsional) galloping (primarily 30°–180°) shows no obvious change with varying ice non-uniformity coefficients. The study concludes there is no significant relationship between the icing non-uniformity coefficient and the Nigol galloping angle range.

Significance and Claims
The paper claims to elucidate the specific impact of ice shape non-uniformity on conductor galloping, a factor previously under-researched. By introducing the ice non-uniformity coefficient, the study provides a quantitative framework for analyzing how asymmetric ice distribution alters aerodynamic stability. The primary contribution is the demonstration that increased non-uniformity significantly expands the instability window for vertical galloping (Den Hartog mechanism) but has negligible impact on torsional instability (Nigol mechanism). These findings offer a theoretical basis for improving early warning systems and mitigation strategies for ice-induced disasters in power grids, particularly for lines traversing harsh environments where non-uniform icing is prevalent.