PD diagnostics on rotating machines. Possibilities and limitations

A short overview is given of typical PD sources within large rotating machines. Characteristic pros and cons of online and offline measurements are presented and their significance with regard to condition based machine maintenance is discussed. The possibilities as well as the limitations of PD measurements as a tool to assess the insulation conditions of rotating machines are outlined. Examples are given for online PD measurements on generators that allow a clear diagnostic decision and therefore a reliable condition assessment to be obtained. However, it is additionally shown that PD measurements have some intrinsic limitations and therefore can not detect virtually all insulation related problems.