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Research of Generator Stator Bar Insulation Detection based on Isothermal Relaxation Current Method

In this paper, a non-destructive method based on isothermal relaxation current (IRC) theory was used to diagnose the insulation condition of stator bar specimens during thermocycling aging. One thermocycling aging cycle is “room temperature-160 °C - room temperature”. In test cycle, five specimens were taken out to do insulation puncture test except IRC test. IRC test includes three steps, i.e. polarization, short circuit and depolarization. The experiment results show that the post curing exists during thermocycling aging process. According to IRC-Analysis, the trap distribution in the insulation could be obtained. The result shows that the degradation of stator bar with anticorona coating is mainly caused by the weakened interface bonding strength through the analysis combined the trap distribution and residual breakdown voltage. Meanwhile, a third exponent decay model was used to reduce the effect of noise.