One of the most important steps for becoming a world class manufacturer is to implement an improvement tool to identify and eliminate production losses. The Anode Service Plant (ASP) in the aluminium manufacturer Hydro Aluminium has become a proactive working plant with respect to Lean Production and Total Productive Maintenance (TPM). The ASP has employed the Overall Equipment Effectiveness (OEE) concept to monitor the equipment related losses of the production system. The challenge was to find a calculation model to identify these production losses without loosing the whole picture of the production system. The model should on the one hand support the management for strategic decision making and on the other hand support the operator in his daily improvement work. The theoretical part of this thesis acquaints the reader with terms of Lean Production, TPM and the related tools. Furthermore a comprehensive research on the OEE concept is provided. It turned out that the models in the literature are only partly appropriate for the ASP. Therefore it was required to adjust the model for the needs of the ASP. The established model is extensively treated in the practical part of the thesis. The analysis of the existing system shows the complexity regarding the data collection. In the description of the model are the production losses discussed and also which contributing factor of the OEE is influenced. Furthermore the visualisation of the losses is presented and discussed. The specifications for the existing systems show the requirements for an automatic data collection. Due to the high number of the existing equipment this way for collecting data was chosen instead of a manual way. In the observed time period it turned out that no butts and the speed losses are even more important contributing factors to the high amount of unscheduled production losses than the equipment breakdowns. If this trend keeps on it will set the focus of the improvement work on new areas in the production system. After the operators are used to work with the improvement tool, then the next step is to combine the results from the OEE data collection with other measurements from the plant.