Bezpieczeństwo Pracy i Ochrona Środowiska w Górnictwie Number 01/2020

The history of organised forms of mining supervision in Kraków dates back to the Middle Ages, i.e. to the issuance of Statut dla żup solnych (Statute for salt mines) by Casimir III the Great. Mining offices in Kraków operated in various forms depending on the political power and political system at a given time; in modern times they operated as a mining starostwo, a district mining office, or a State Mining Office. The successor to these bodies is the District Mining Office in Kraków, which has been established in its current form by a regulation of 1946. As part of their activity, mining offices in Kraków have supervised the extraction of most of the minerals available in Poland: rock salt, crude oil, natural gas, hard coal, metal ores, brine, healing and thermal waters, rock minerals, sand, and gravel.  In addition, they currently supervise over tourism flows in the historic Bochnia and Wieliczka salt mines and building a tunnel through the Luboń Mały mountain. Those employed in the District Mining Office in Kraków are committed to ensuring safety for persons working in mines, ensuring general safety, and limiting mining effects on the environment.

This paper presents the issue of overvoltages when switching off transformers in actual power supply systems. The analysed power supply networks for transformers are powered from typical mining substation bays with 6 kV vacuum or sulfur hexafluoride (SF₆) circuit breakers or contractors. Given fast technological changes in design solutions for contractors and circuit breakers, switching-off times of supplied circuits have gone down ten times. Shorter switching-off times of supplied circuits cause a considerable increase in voltage once the contractor or circuit breaker activates. Due to the fact that such devices are installed in potentially explosive atmospheres, an attempt has been made to calculate such overvoltages based on actual power supply systems in mines. From the point of view of operation safety, an important result of the calculations is the presence of the pulsatance difference before and after circuit breaker deactivation (ω_N²-ω²) in the denominator of the formula (14) for recovery voltage. This is of cardinal importance for safety. When the value of pulsatance after circuit breaker deactivation (ω_N) is similar to this value before circuit breaker deactivation (ω), the denominator then approaches 0, and recovery voltage  u_p(t) approaches infinity. Therefore, when power services of mines plan to modernise their power grid, it is always recommended to recalculate the portion of the grid so as to avoid the pulsatance value before and after circuit breaker deactivation becoming equal (ω_N = ω).

Environmental law and geological and mining law require mining companies to take the necessary measures in order to protect the environment and ensure land revegetation after mineral extraction. The scale of the issue is illustrated by the volume of land occupied by mining operations in 2017 – 41,017 ha. As part of liquidation and revegetation activities, mining companies often add new landscape values and usefulness, frequently better than the original ones for the environment, to the areas transformed as part of open-pit mining. Among a very wide range of revegetation directions, three main ones may be distinguished: forest, agricultural, and water. Forest-oriented revegetation, carried out by the Szczakowa sand mine in Jaworzno or the Szeligowiec mine in Siewierz for example, involves preparing the land for forest use. Water-oriented revegetation is carried out by, for example, the Przecieszyn III open-pit mine in Przecieszyn and the Dwory aggregate mine in Oświęcim. It involves profiling the slopes of the reservoir and preparing the land for recreational, breeding, or ecological functions. Agricultural-oriented revegetation aims to prepare the land for agricultural or horticultural production.