EVALUATION OF THE EFFECTS OF ELECTRICAL STRESS DURING ACCELERATED THERMAL AGING ON DIELECTRIC PERFORMANCE OF INSULATION SYSTEMS FOR LOW VOLTAGE MOTORS

International audienceThree sets of 10 motorettes were characterized along aging. Thermal agingconsisted of isotherms at 240°C. Electrical aging consisted of the application of an ACvoltage just above the Partial Discharge Inception Voltage (PDIV). Aging sequence was aseries of 6 cycles of 72 hours. In between aging cycles, the evolution of PDIV andInsulation Resistance on Coil-Coil and Coil-Ground configurations were monitored.Polarisation Index provided by the ratio of measured resistance after 10 min and 1 minwere calculated. As concerns thermal aging, PDIV decrease was of 10 to 22%. Thisdecrease occurred mainly after the first aging. Electrical aging under partial dischargeactivity can be revealed by a significant increase of the Polarisation Index. Electricalaging led to 90% failure during the third aging cycle with typical PD-free EIS while none ofthe motorettes with strengthened EIS were affected during six cycles. PD analysisrevealed with the strengthened paper a specific behaviour consisting in a discontinuousregime of discharges