Does anyone have experience with premature winding failure on appropriately derated LV motors installed above 3000M on Inverter PWM? I am looking for data that would help to explain some premature motor winding failures (multiple manufacturers) on VFD (multiple manufacturers) driven motors in high elevations. Some motors are VPI, all are inverter rated. Voltage varies from 460/480V - 575 and 690V. PWM varies from 1.5 - 3kHz. The failures are not seen at elevations below 3000M and the actual analysis of the failed motors are unreliable. Motors are appropriately derated for elevation in all cases.