A device for supervising different positions of a valve of a high voltage converter station located on a high voltage potential level comprises members arranged on a high voltage potential level and adapted to detect function parameters of the valve on a high voltage potential level and send values detected thereby to first control units for controlling the semiconductor components of the valve. The first control units have devices for processing the detected values and the first control units are adapted to utilize light conductors running back therefrom to a valve control unit for sending data resulting from the processing to an arrangement for supervising the valve located on a low potential level.