The master’s thesis covers analysing of the use of lightning protection in substations. The first part presents the theoretical approach of the formation of lightning discharges and reasons for probability of direct lightning strikes to object. Then are presented methods for the analysis of protection against direct lightning discharges. The rolling sphere method which is also used in simulation calculations is described more in detail. The purpose of the master’s thesis was to determine the most optimal method for calculating the radius of a virtual sphere in the analysis of lightning protection in substations with the rolling sphere method in our country. The radius of the rolling sphere depends on the current against which we want to protect the devices in the substation and two constants that have been empirically determined over the years, based on electrogeometric models, by various researchers. Based on the analyzes of the model of the substation, I compared the calculations of radii according to five selected different methods (different constants used) and found that for the currents used for the coordination of lightning protection in Slovenia, the most conservative method for calculating radius is according to the findings of the Institute of Electrical and Electronics Engineers (IEEE), and the least according to the determination of radii by the standard IEC 62305-1. The latter is the most adequate from an economic point of view but the least from the point of view of the degree of reliability of protection against lightning strikes. Taking into account both requirements, the calculation using the constants determined by Brown proved to be the most suitable method for calculating the radius of a rolling sphere.
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