In the paper the carried out and applied works concerning a using diagnostic studies for the estimation of present and future state of electrical equipment in railway traction vehicles have been described. Results of a few research works concerning selected elements of electrical supply system and traction drive as well possibility of practical their use in the vehicles exploitation also have been presented. In the end of the pa-per solution of a diagnostic system worked out and applied by Rail Vehicles Institute “Tabor” implemented on type EU07 locomotive have been presented