The following master’s thesis presents reconstruction analysis of the existing 110 kV air-insulated switchgear in the distribution substation 110/20 kV Jesenice. The first chapters presents the criteria, which are important in the reconstruction and theoretical background of the high voltage substations. Further, the reasons and causes for the reconstruction of the high voltage substation are described in more detail. The dimensioning of equipment on normal and short circuit loads is carried out. Two possible solutions of the integration of Jesenice distribution substation into the 110 kV Slovenian electric power system are shown. The second part shows the systems for protecting and management of the new gas-insulated metal-enclosed high voltage switchgear. In the final parts of this thesis, the reconstruction and updating of the existing grounding system is shown. The design and calculation of lightning protection for the new building of high voltage GIS is presented in the form of detailed analysis.