Pulse-count distribution as a possible diagnostic tool for assessing the level of degradation of rotating machine insulation

A method is presented by which one can qualitatively assess the condition of epoxy mica insulation systems used in large rotating machines as a function of time. Experimental techniques for acquisition and analysis of failure data are presented. Experiments were conducted 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. Diagnostic measurements such as incremental loss tangent, capacitance change, partial discharge pulse count/magnitude, and PD energy were performed along with destructive measurements (dielectric strength). There appeared to be an excellent correlation between pulse count/magnitude and dielectric strength. This fact can be used in the assessment of the degree of degeneration of the insulation