Evaluating Turn Insulation Degradation Using Sweep Frequency Response Analysis

Turn insulation in stator multiturn coils is often involved in machine failures. To date, however, there are no tests for determining the long-term performance of turn insulation. Conventional diagnostic tests (partial discharge (DP) and dissipation factor (DF) measurements) are not accurate for the detection of turn insulation degradation. Sweep Frequency Response Analysis (SFRA), based on analysis of winding impedance in the frequency domain, has been used for more than 40 years to diagnose power transformer windings, and its application in rotating machines is currently the subject of research. The aim of this study, is to evaluate the SFRA capability to assess turn insulation degradation by the insertion of fault resistances between turns at three locations on a spare coil. SFRA measurements were compared to a numerical simulation using an RLC model representative of the stator coil.