## 1 Introduction  
The transmission network is the core of the power system, connecting electricity consumers to power plants. Due to its key position in the system, the transmission network must be an element that guarantees uninterrupted transmission of electricity to consumers. It should also be remembered that reliable production, transmission, and distribution of electricity to consumers is the primary task of the distribution system operator [1, 2, 3, 4, 5]. Therefore, with the increase in the number and capacity of installed generating installations, and due to the age of transmission lines and system transformers [6], appropriate maintenance scheduling plays an increasingly important role [7]. For this purpose, in [8], the authors used the strategy of preventive maintenance for line reliability by assigning priority to each of the analyzed objects based on indicators that define its importance in the system and its technical condition. A similar issue was addressed in [9, 10, 11]. Due to the continuous and unceasing development of power networks, the topics discussed in this publication may allow for further improvements in reliability for overhead transmission lines and system transformers. It should be noted that a large part of the articles related to the resilience of energy systems [12, 13, 14, 15] and the decisions taken in connection with it [16, 17, 18, 19] in the eventof a sudden-onset disaster mainly focus on the phases planned before a disaster occurs or already in the post-disaster phase. This makes the work of [17] all the more valuable, where the authors present a concept that allows one to create a time window for decision-making, which can save a power system in the event of such an emergency. There are various definitions of reliability in the literature [20; 21; 22; 23; 24]; however, the authors of this article define it as the ability of the elements to achieve the set goals without exceeding the required parameters. The available literature on reliability issues is quite extensive, but only a small part of it refers to transmission lines and transformers. Such work can certainly include [25; 26; 27; 28; 29]. This is because using increasingly accurate mathematical models to determine reliability requires collecting a large amount of data that is not publicly available, and operators of both distribution and transmission systems are reluctant to provide it. The following coefficients are used to assess reliability:  
* AENS (Average Energy Not Supplied);
* AIT (Average Interruption Time);
* ENS (Energy Not Served). In [30; 31], the authors show that the main causes of unplanned overhead line failures are unfavorable meteorological factors such as gusty winds or lightning. The authors of these works analyze the Chinese power grids, and in 2011, these factors were responsible for more than 84% of all unplanned outages and failures. In the papers [32; 33; 34; 35], the effect of wind conditions on the performance of the power system was studied. The work [32] presents a case study for a section of a 230 kV line, examining the behavior of the line under different wind conditions. Atmospheric factors that affect the reliability of the power system as a whole and its elements, such as transmission lines, are considered by the authors [36]. Also, in [37], reliability indicators are presented about weather conditions. To ensure the reliability of power grid operation, one of the methods used is a precise assessment of lightning risk, along with ongoing diagnostics of damage to network elements [38; 39; 40]. In the case of assessing lightning hazard in 110 kV distribution lines and 400 kV transmission lines, such an assessment is made based on the number of lightning strikes in the line or possibly on the number of outages of a given line during the year. More information on this subject can be found in [41]. It is also important to determine the time it takes to eliminate the failure and restore the system to its proper condition.