The paper shows the development of a knowledge based system to evaluate the technical condition of a hydro power plant including its components. This system analyses the condition of the components by evaluating selected influencing parameters and together with selected parameters about the whole power plant, it leads to statements about the existing refurbishing potential and the urgency of refurbishment measures including a priority list of technically advantageous component refurbishments. A subsequent economic evaluation analyses the influence of several economic influence parameters on the optimum refurbishing time. Finally results of case studies including sensibility analysis of the influence parameters will be shown.