Testing of electrical conductivity of bentonite „Bentoplast 20“ Petrokemija d.o.o. Kutina
Abstract
Due to the accessibility of bentonite and its relatively good properties, bentonite grounding mat is most often used in our region to improve the characteristics of grounding conductors in poorly conductive environments, especially dynamic characteristics (atmospheric discharges, etc.). Bentonite is a volcanic clay, containing minerals (Al2O3, Fe2O3, MgO, CaO, Na2O, K2O) that form electrolytic conductors with water. Bentonite does not leach out of the soil, so the mat does not need to be renewed. However, bentonite is also an electrolytic conductor, so it requires a certain level of moisture. Completely dry bentonite clay has a very high electrical resistance (significantly higher than 1000 Ωm). Since bentonite clay is very hygroscopic, in normal climatic conditions it is possible to expect good conductivity of the mat without special maintenance. However, it is important to know that the salt conglomerate in bentonite and their relative share is not firmly determined, so the conductivity of bentonite from different deposits can vary. Therefore, it is good to determine the characteristics of the specific material by measuring. By adding water in a ratio of 1:1, the resistance of bentonite decreases by about three orders of magnitude. With further addition of water, its resistance increases insignificantly. Unlike metal conductors, the temperature coefficient of wet bentonite is negative, but the change in resistance in the range of 4°C to 40°C is not radical (it changes in the range of 3.6 m – 2.2 m). It was further observed that by drying bentonite mud, its density increases significantly, its plasticity decreases, but its electrical resistance does not increase radically as a result. It is also observed that the dried sample retains its hygroscopic properties. Based on all of the above, it can be concluded that wet bentonite is a suitable material for the bedding of grounding conductors.
Stanko Milun
Full Professor
Faculty alumnus with a research focus in the development of measurement methods in high-voltage systems, signal analysis in electrical power systems, and the application of geoelectrical methods in energy infrastructure. Prof. Milun has been involved in numerous scientific projects, including those related to the optimization of grounding systems for high-voltage plants and the development of transient measurement methods. He has authored 38 scientific papers and over 150 professional studies.
Goran Petrović
Full Professor | Department of Electrical Measurements
Prof. dr. sc. Goran Petrović is a full professor at the Faculty of Electrical Engineering, Mechanical Engineering and Architecture in Split. His research interests include measurement of electrical and process quantities, analysis of geoelectrical and geothermal features of the soil, instrumentation for smart grids, measurement and application of synchrophasors. He is the author of numerous papers published in top-tier scientific journals and contributed to valuable international and national scientific projects.
