Experiences with online partial discharge diagnoses on turbogenerators

This paper describes the experiences with partial discharge diagnoses of high voltage turbogenerators. After a short introduction of the structure of a high voltage winding with Roebel-bars the sources of partial discharge in the winding are described. The phase resolved partial discharge pattern analysis as well as the applied method for online and offline partial discharge measurement are described and practical measurement results for offline and online diagnoses are presented. The important link to maintenance actions is outlined for a typical case. In an example the fingerprints of offline diagnoses and online diagnoses of the same generator are compared. Also the change of the fingerprint over a period of three years is presented. The degradation of the insulation in the first period due to increased operation voltage and the fingerprint after maintenance actions during the second operation period are shown. The interpretation of the partial discharge fingerprint is discussed for presented examples. Many typical partial discharge patterns have been collected and classified for many years. Therefore, it is possible to identify fingerprints at the very first online measurement. An example is presented.