Assessment of remaining insulation life of high voltage inductionmotors

摘要

Various insulation tests were performed on the aged polyester/micainsulation of 3-6 kV rating motors. About 100 machine samples have beenretrieved after 11-22 years service in the field and tested beforerewinding. The tests include measurements of insulation resistance,polarization index, dissipation factors, partial discharges, and ACbreakdown voltage. The insulation resistance and polarization index tendto decrease with operating time, while the dissipation factor tip-up andpartial discharges show no clear tendency. The breakdown voltage showsgradual decrease with operating time. A good correlation is foundbetween the remaining breakdown voltage and a new index log (R_d/R_w), where R_d andR_w are the insulation resistances measured under dryand wet conditions, respectively. Using these test data and a modernsoftware tool, the authors have developed a prototype expert system fora diagnostic consultation