Stator winding insulation is the part of the hydrogenerator experiencing the highest number and the most damaging failures followed by long down times, costly repairs and large economic losses due to interrupted generation. In addition, changing operation patterns from base load to intermittent for the Norwegian ageing hydrogenerator population, have created a need for knowledge of the actual condition of the insulation. This calls for research on new condition monitoring methods. This project will accommodate and evaluate promising variable frequency methods currently adopted by other high voltage apparatuses such as transformers and cables. These methods are likely to provide more valuable diagnostic information of the stator winding insulation condition compared to other methods in use today. Hydrogenerator stator bars from storage or service as well as model bars will be included in the project. The measurements will be related to actual failure mechanisms and classified in terms of condition states. The condition state of stator winding insulation is essential in making correct maintenance and renewal decisions. In this work, financial support from the Norwegian Research Council is essential to establish fruitful co-operation between Norwegian and foreign hydroelectric power companies, NTNU, SINTEF Energy Research, Institut de Recherche d'Hydro-Québec (IREQ), EDF, KTH and the University of Uppsala.