The aim of this thesis is to investigate and address the issue of leakage on the bolted joint between the cover and the tank of power transformers. The theoretical part presents the fundamentals of bolted joints and quality management tools. The experimental part describes the initial condition of the bolted joint between the cover and the tank. Using basic quality tools, namely the Pareto chart and Ishikawa diagram, an analysis was carried out to identify the most influential causes of leakage. Based on the results of the analysis, corrective measures were introduced into the transformer manufacturing process to reduce the possibility of leakage occurring. A new bolting method was implemented using continuous tightening tools with specified tightening torques and a defined bolt tightening sequence. The use of thicker DIN 7349 washers and a new bolt lubrication procedure was also introduced for the bolted joint. The implemented measures ensure greater control over the bolting process and reduce the possibility of leakage occurring in the bolted joint between the transformer cover and tank.
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