Turbine generator ground current arcing detection apparatus and method

Abstract

Changes in flux density in large rotating machinery induce a voltage in the rotating shaft of the machine. The shaft is isolated electrically from the machine frame so that currents do not flow from the shaft to the frame toward ground potential. Apparatus and method is provided for detecting arcing current between the shaft and support bearing surfaces which may occur upon failure of the insulation which isolates the shaft from the frame. The method involves monitoring the high frequency voltage components developed between the support bearings at opposing ends of the rotating shaft. The apparatus includes an electrical connection at each of the two shaft support bearings. The two connections are brought to the input of a high pass filter. The high frequencies passed by the filter are connected to the input of a radio frequency detector which provides an output indicative of the high frequency input. The high pass filter and detector are isolated from ground so that there is no path for arcing current to ground provided through the apparatus. The detector output is optically isolated from and coupled to a device for displaying the presence of voltage signals in the high pass band which are indicative of arcing current and subsequent pitting at the bearing-rotor shaft interfaces.