Premature motor winding failures on VFD driven motors in high elevations

Explaining 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.

As though the problem is universal across different manufacturers, the problem lies somewhere in the installation. This may due to the usual suspects of Voltage, Harmonics etc. As it pointed out, the problems do not appear below 3000m. Now this is a guess only as have not had experience in high altitude installations and someone more knowledgeable could confirm this, but when derating for these altitudes, need to apply a correction factor. In aviation, performance of an aircraft is 'normalised' by applying a temp factor over altitude. This accounts for the air density, less air, less lift and maybe less cooling in this application? For example at 2000 feet and a temp of 28 Celcius, gives the aircraft a performance equivalent to say 3500' or so. When manufacturers state a derating factor, we need to take this into account.

Not all Motor/VFD combinations have reactance in the output and it looks to be a plant wide phenomenon based on the description. De-rating already having been addressed tells us that these failed units are not failed due to thermal degradation. Since variable frequency drive connected motors are the only ones mentioned, assume the motor started with ATL and RVSS are not having high rates of failures. we would start at the plants transformer and meter the mains voltage, check plant ground.

Extreme altitude (4500m+) VFD applications required voltage derating to prevent corona at reduced atmospheric pressure - essentially, 575V rated VFDs operated at 380V, and motors wound with insulation suitable for 480V inverter duty (sea level).