Diagnostic tests on insulation of old windings prior to rewind can add much to an understanding of the mechanism leading to failure in a machine as well as the relative effectiveness of the various test methods for evaluating insulation condition. An excellent opportunity to make such a study occurred when plans were made to replace the entire stator of a 40,000 kva, 13.8 kv, 81.8 rpm waterwheel generator in service since 1927 at the Cono-wingo Dam of the Philadelphia Electric Company. Thus, a series of exhaustive tests could be made on the original stator winding without delaying the planned outage.
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