Repeated motor winding failure of IngersollRand Screw Air Compressors 75 kW

Hello Colleagues,

What can be the root cause of repeated winding failure of two identical 75KW air compressors motors? The motors are controlled via a VSD.

No earth fault was detected. So, Is it only about wrong settings? Does anybody knows about the overcurrent and short circuit protection methodology in the VSD? what should I check?

Unfortunately, it is not mentioned in the compressor user manual how to see the VSD settings. I would appreciate if somebody send me the advanced manual of IRN75K in order to investigate this issue.

How long between replacing the motor did the fault occur again? Could be overcurrent demagnetizing the motor from the VSD, shaft alignment, temperature, etc. Protections are device specific, you'd have to look up the particular VSD and compare settings to recommended. Verify with the vendor as well
Thank you MicrobicTomb for your feedback. We have changes 3 motors within 1 year.

Would you please clarify what do you mean by " Protections are device specific"?

Thank you!
Device specific in the sense of what options are available to you. For example, does the VSD have overcurrent protection? If so, what are the ratings? Verify with the manufacturer or manual to make sure all the settings/parameters are correct. (Do you have an air compressor vendor who can supply you with the manual or feedback on settings for the VSD?)

If it were me, I'd check the basics first. What's the voltage look like, how's the current out to the motor, monitor the current to the motor during normal operation, force higher current during monitoring by starting up with lower than normal pressure out. Are there any audible changes to normal operation? A hum or vibration that wasn't present before?
Are you using motors that are designed to be operated from VFDs? VFDs can create phenomena that can cause high voltage spikes to travel from the VFD to the motor windings and damage the windings. This can happen very quickly if your motor was not designed with newer higher voltage insulation. The terminology in the motor industry is "inverter duty", and although that has no "official" definition that everyone agrees on, it's still a good place to start.

If you have older motors that are not "inverter duty", then you should add filters to the output of the VFD to try to protect them from those voltage spikes. However you can often spend more for a filter than you will pay for a new inverter duty motor.