Assessing the Level of Degradation of Rotating Machine Insulation

The work covered in this paper pertains to a method by which one can qualitatively assess the condition of epoxy mica insu-lation systems used in large rotating machines, as function of time.-Experimental techniques for acquisition and analysis of failure data have beeh presented. Experiments have been con-ducted on actual rotating machine coils subjected to combined electrical and thermal stress, under simulated conditions, so as to reflect the service environment as far as possible. Diag-nostic measurements such as incremental loss tangent, capac-itance change, partial discharge pulse count/magnitude, and PD energy have been performed along with destructive mea-surements (dielectric strength). Excellent correlations between pulse count/magnitude and dielectric strength appear to be present. This fact can be used, in the assessment of the degree of degeneration of the insulation