The Aging of the Insulation System of Large Rotating Machines in Frequency Domains

The insulation of stator winding in a rotating machine consisted of mica and epoxy resin materials. The structure was also composed of junctions, so, a diagnostic monitoring condition of this insulation was taken into consideration. First, the results of the polarisation and depolarisation current measurement (PDC) of the test sample (stator winding rate of 13.8 kV) were investigated, as an experiment in the laboratory. The conditions of the experiment were conducted under different thermal stresses of 25°C and 100°C. The test sample was full stator bar. As found, the trend of the temperature of the winding rise if the current of the polarisation and depolarisation was increased. Second, the results of the PDC were calculated from the time domain to the frequency domain. The aim found that the aging point of the insulation system should take into consideration the results of the calculation of the frequency domain. The aging of the insulation system was a variant by the thermal stress, which was an effect from the complex capacitance and polarisation losses in the insulation winding system. Finally, this identified the phenomenon of the aging of the machine insulation system.