**1. Introduction**

To reach the consumption areas, electricity often travels large distances through power transmission lines due to the remote location of most power plants, crossing different climatic environments. These transmission lines are often exposed to various stresses influencing their operation, causing in some cases different outages. Power grid infrastructures in many countries around the world are consequently impacted by ice and snow accretions. Some countries in the arctic region, such as Canada, the United States, Russia, Iceland, and Scandinavian countries, have been exposed to these problems since the deployment of electricity networks [1–3]. Additionally, power lines crossing mountainous areas are prone to ice and snow, for example, in China or Italy [4,5]. Furthermore, climate change leads to more and extreme weather events in various countries [3]. As the impact of ice and snow accretions is more intense for temperatures close to the freezing point, the occurrence of critical situations may not be limited to the known cold regions of our planet.

Associated to the ever-growing world's population and faster industry development, many power grid projects have been commissioned or are underway around the world. The impact of snow or ice events consequently gained importance. Extreme reliability is therefore demanded for electricity distribution. When failures occur, they inevitably lead to high repair costs, long downtime, and potential risks to human safety. Therefore, a variety of countermeasures against atmospheric icing of power lines were proposed in the past to avoid or at least to minimize power outages during such ice or snow events. Pohlman et al. [1] in 1982 firstly reviewed the various anti-icing and de-icing methods

**Citation:** Brettschneider, S.; Fofana, I. Evolution of Countermeasures against Atmospheric Icing of Power Lines over the Past Four Decades and Their Applications into Field Operations. *Energies* **2021**, *14*, 6291. https://doi.org/10.3390/en14196291

Academic Editors: Abu-Siada Ahmed and Andrea Mariscotti

Received: 2 September 2021 Accepted: 27 September 2021 Published: 2 October 2021

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known at that moment. Since then, various other reviews and technical reports have been published [2,6–11]. In the framework of the present contribution, the evolution of the proposed countermeasures over the past four decades was analyzed by comparing these reviews. In the second part of the article, a few study cases focusing on the selection of methods for field applications or further investigations were examined based on the publications [4,5,12–16].

It may be noted that it is not the intention of this article to provide detailed information on each individual anti-icing and de-icing method. This information can readily be found in the various publications cited in the article.

For the general understanding of the importance and possible impact of snow and icing events, some information on two examples of important cases of ice storms are provided. Furthermore, some general information on the distinction of anti-icing and de-icing methods as well as on the general impacts of snow and ice on power lines are included.

#### *1.1. Two Examples of Extreme Ice Storm Events*

Similar to any meteorological event, snow and ice storms do not occur on a regular basis. However, some areas of the world may experience these events more or less recurrently. Rarely, extreme icing events occur with disastrous impacts on a larger region. Two of such catastrophic events may be recalled here:


#### *1.2. Anti-Icing and De-Icing*

The literature uses commonly the two terms: "anti-icing" and "de-icing". The first term, "anti-icing", is used for the approach where it is intended to prevent any accumulation of snow or ice on the power lines. The second term "de-icing" identifies the approach where existing ice or snow accumulations are to be removed [2,8]. Some methods are efficient for one or the other approach. For example, icephobic coatings are a measure against ice buildup [8], whereas mechanical methods such as manual scraping or roller wheels are used to remove the ice or snow that was already accumulated [2]. Other methods such as heating of the conductor may be applied for both approaches [5,9]. More details on the distinction between anti-icing and de-icing methods can be found in the appendix B of [6] and in reference [11].

**Figure 1.** Example of icing impact on a high voltage transmission line (1998 Eastern Canada ice storm, credit: Photo Hydro-Québec).

**Figure 2.** Example of icing impact on a medium voltage distribution line (1998 Eastern Canada ice storm, credit: private archive).

#### *1.3. Consequences of Ice and Snow Accumulations on Power Lines*

The impacts of ice or snow accumulations on power lines are already well documented by different authors, e.g., [1,8,11]. It should be mentioned here that the impacts for power lines are mainly of a mechanical nature. The increase in the static load is important due to the additional weight of ice or snow accumulations (for example, ref [15] mentions up to 100 kg/m) and it may push the supporting structures to their limits. Furthermore, dynamic forces may become problematic, either due to galloping of conductors or ground wires or during the shedding of the additional weight. If two adjacent spans of a standard tower shed their ice load at different moments, the tower may be subjected to lateral forces beyond its designed limit.

Electrical failure may also occur in some cases [11]. Conductors of different phases may ge<sup>t</sup> close or in contact due to unequal accumulation or dynamic wind forces. Induced corona discharges may increase power losses or electromagnetic interferences. Finally, ice-covered insulators may experience flashover, especially if the line is subject to pollution or salt deposit (natural from the sea or artificial near highways) [11]. A review of the present stage of knowledge of outdoor insulator flashover is presented in [3].
