3.1.3. Passive Coatings

Coatings are applied to the conductor to avoid or at least limit ice or snow accumulations. Passive coatings do not require any external energy, but modify the surface properties of the conductors with the aim of weakening the adhesion forces of water droplets, ice or snow on the conductor surface.

## 3.1.4. Active Coatings

Active coatings use external energy to prevent or limit the accumulation of ice or snow on the conductor surface. Various principles are proposed to prevent or reduce any accumulation, such as heating due to the increase in losses, addition of heating tracers or the reduction in ice adhesion forces through ice electrolysis.

## 3.1.5. Mechanical Methods

Mechanical methods use different principles to break off the accumulated ice or snow. The forces required to break the ice may be applied by linemen with isolated poles or tools pulled by ropes or also from helicopters. Other methods consider apparatus that are installed on the lines temporarily or on a permanent basis. For bundled conductors, the force to break the ice may be generated by a temporary short circuit.

## 3.1.6. Thermal Methods

Thermal methods use different principles to heat conductors and ground wires in order to avoid any accumulation of ice or snow or to melt off existing accumulations. Different energy sources may be used; for example, the energy of the power network itself through load shifting, external current sources such as DC injection or high frequency injection or other external heat sources.

## 3.1.7. Miscellaneous Methods

This last group covers methods that were reported in some reviews and that did not seem to fit in any of the six preceding groups [2]. Some methods are still at a conceptual stage and their feasibility was not ye<sup>t</sup> validated. Other methods were mentioned, but their applicability to power lines does not seem to be efficient [2]. The method 7.8 for asymmetrical operation of a three-phase power line was not included in any of the analyzed review publications, but was mentioned during the public hearing process for the authorization of the construction of the Levis de-icer project by Hydro-Québec [18]. It was therefore included in the last group of this study.

#### *3.2. Comparative Analysis over the Last Four Decades*

Figure 3 shows the chronology of the analysed review papers in relation to the two catastrophic icing events. It can be recognized that the number of proposed anti-icing and de-icing methods increased significantly between the 1980s and 1990s, but there is no remarkable increase in the number of countermeasures during the last three decades. A large variety of methods for anti-icing and de-icing was already proposed in the 1990s, before the two catastrophic icing events in 1998 and 2008. However, the compilation in Table 1 does not show the degree of advancement of the individual methods at the moment of publication. For example, icephobic coatings were already mentioned as a potential countermeasure by Laforte et al. in 1996 [2]. At that time, the stage of advancement for this

passive method was indicated as "in development". Intensive research efforts have led to important advancements in the field of icephobic coatings and surface treatments, as witnessed by recent CIGRE working group activities [19,20]. However, additional efforts in research and development are still required in order to come up with effective and durable solutions for practical applications [20].

**Figure 3.** Chronology of the analysed review papers in relation to the two catastrophic icing events.

The compilation in Table 1 allows two more observations. The analyzed documents before the 1998 Eastern Canada ice storm [1,2] did not include any countermeasure in the field of line design (group 1 in Table 1). Perhaps these methods were initially not considered as countermeasures, because no additional equipment is required. Nevertheless, it can be noted that the knowledge on the positive effects of line design considerations has increased with the experiences gained from various icing events over the past few decades. As shown in the second part of the study (see Section 4.2), several line design measures have been implemented after the 1998 ice storm in Eastern Canada. Reference [11] indicates that these approaches present the best prevention technique for new constructions, but should be seen as complementary to the other countermeasures in order to obtain an optimized protection of power lines against icing events.

The second observation shows that in more recent articles, the miscellaneous methods (group 7 in Table 1) that were proposed in the two documents of 1996 and 2002 [2,6] were no longer included. One might understand that the applicability of these more theoretical approaches has not been demonstrated and that research institutions and electric utilities focused their efforts on the development of already known countermeasures that showed greater potential for practical applications in the field.

#### **4. Selection of Countermeasures for the Integration into Field Operations or for Further Investigations**

Four example cases were reviewed for the selection or recommendation of counter measures for field application. The results are compiled in Table 2. The first column is similar to the one of Table 1 and lists the countermeasures that were proposed over the past four decades. The other columns present the various methods that were considered in the four example cases. The bold and capital letters indicate the methods that were selected or recommended for field applications or further investigations.

#### *4.1. Technology Integration within Hydro-Québec after the 1998 Eastern Canada Ice Storm*

References [12–14] show the analysis performed by Hydro-Québec after the 1998 ice storm in Eastern Canada. Eleven countermeasures were considered and a detailed evaluation of each method using several criteria was carried out. This analysis allowed assigning a score to each method and establishing a ranking. The numbers in the second column of Table 2 represent the results of this ranking. The two methods with the highest scores were:

	- − Approval for the project was obtained in August 2004 [21].
	- − The engineering for the de-icer project was completed in 2005 [22].
	- − In 2008, the commissioning of the de-icer project was completed [23].
	- − However, the de-icer could not be used until today. One of the main reasons for this blockage is the risk of ice pieces falling onto highways and damaging cars during the de-icing period. Therefore, Hydro-Québec started installing the LC-spirals (method 4.2) on the power lines above highways in 2017 [24]. These installations are relatively difficult to schedule as the highways have to be closed temporarily. The installation efforts are scheduled through 2023 in order to cover all critical highway crossings.

Hydro-Québec did not only rely on these two methods. The following other countermeasures were integrated into field operations on the Hydro-Québec power network:


Furthermore, several line design considerations are adapted to strengthen the network against impacts of future winter storms [27]:


Another example for the improvement of network design is the construction of a new line for the interconnection of a windfarm in 2011. This line had to be constructed in an

area with particular weather conditions that favour the accumulation of important ice loads. The following line design considerations were applied in this particular case [28]:


**Table 2.** Summary of the countermeasures that were selected for application or future investigation in four different countries.



#### **Table 2.** *Cont.*

#### *4.2. Recent Applicability Studies in Italy*

Even if Italy is not an arctic country, it experiences major power outages from time-totime, mainly due to wet snow accretions. Reference [5] presented an analysis of various anti-icing measures for the Italian power system including recommendations for the implementation of a new method. Until now, two passive methods have already been in use: in 2019, about 20,000 counterweights (method 2.1) were installed on 2500 km of 132 kV lines, which led to a significant reduction in power outages due to snow overload. As the second countermeasure, interface spacers (method 2.3) were first installed on some critical spans of 132 kV lines in 2007. Due to the success in eliminating phase-to-phase faults, about 28 km of double circuits were equipped in 2019 with these devices.

As there are some local areas that have recurrent service disruptions due to wet snow accretion, the applicability of thermal anti-icing was studied. Detailed load flow analysis showed that load shifting (method 6.1.1) would not allow obtaining the current magnitudes that would be needed to create sufficient heat in the conductors. Moreover, the installation of shunt reactors (method 6.1.3) at critical locations allowed the creation of sufficient current flow. Thus, the Italian network operator started a program for the installation of shunt reactors at different critical sites. It is noted that the addition of these shunt reactors might also be beneficial for voltage regulation in the local networks.

#### *4.3. Recent Applicability Studies in Norway*

A recent applicability study of anti-icing and de-icing technologies was presented by [15] for the Norwegian power grid. Presently, the main method for de-icing of power lines consists of the use of helicopters that strike the lines with a pole attached to an insulated rope (method 5.1.5). Several technologies were investigated in order to verify if they could be applied in the context with the specific conditions that prevail in Norway: mostly in-cloud icing, extremely non-uniform ice loads, sometimes only on a few spans, with difficult or no terrestrial access to the lines due to complex topography and remote areas.

A workshop was organized in October 2018 where about 80 international specialists gathered and presented the current development state of various methods. Nine methods were retained for further analyses as these were considered potentially applicable to the Norwegian conditions. The following preliminary recommendations were formulated in [15] in order to identify the methods that should be further investigated:


#### *4.4. Recommendations after the Winter Storm of January 2008 in China*

The important icing disaster in large parts of southern and central China in January and February 2008 led to intense research efforts and an important number of publications similar to the development that could be observed in Québec after the 1998 ice storm. As examples, two reviews [4,16] were included in the present analysis. It should be mentioned that China experienced an increase in the high voltage DC line projects during the last years. Therefore, Li et al. [16] elaborated various technologies designed for thermal de-icing of DC power lines (method 6.3). Lv and He [4] concluded that the development of de-icing methods for power lines are expected to follow a trend towards mechanical de-icing based on robots (method 5.1.6).

In another publication by a joint team of experts from university and power companies [29], Jiang et al. reported on the strategies and status of anti-icing methods that were studied in China after the 2008 ice storm. Various countermeasures applying coatings, laser technologies, and robots as well as AC and DC de-icing techniques were tested. It was found that the thermal de-icing method using DC voltage (methods 6.2.3 and 6.3) is a convenient solution with relatively low power demand and high efficiency. According to Jiang et al. [29], more than 200 substations have been equipped with fixed DC de-icing systems and mobile ice-melting devices are also employed by various utilities. Two years later, Jiang et al. reported ongoing research efforts with emphasis on the load current transfer method of bundled conductors (method 6.5) [30].
