It is a 2100HP induction motor, 12 poll. Inverter IGBT's fire at about 12Hz (electrical frequency) so at about 2.5% slip motor runs at 117rpm (full load HP).
Here is my question: Should the inverters be derated because they are firing at such low frequency (12 Hz)? My boss thinks so and I am not sure because I don't see why and I have not found any reference online indicating so... :?
LMAO, there have been a lot of off question replies here, including lots of questions about whether your motor that is apparently running fine without overheating running 12hz, 117rpm, is capable of running fine at 12hz, 117rpm...,,,
Your OP was whether the DRIVE needs derating. You have seen lots of questions about what the motor nameplate rating is. Can you provide that? If so, a lot of the off topic replies can be answered.
Bottom line I see is you asking if a particular drive can run at 12hz w/o derating. Again, we cannot answer this but your drive mfgr can. I suggest you not get sidetracked with the motor heating issues if that is not a problem but rather find if your particular drive fgr can handle 12hz full nameplate current at 12hz. Have you asked them? what have they replied?
so since your motor IS rated 117rpm@12hz BASE speed, back to your OP question: can your present drive handle this without derating: Again, you must ask your drive mfgr if it can - we will asll give you guesses based on our experience. The only way we can say NO IT WON't is IF YOU GIVE US MOTOR NAMEPLATE DATA AND DRIVE NAMEPLATE DATA. Then we can compare the two and show you if the drive AMPERAGE rating is LESS than the motor amperage rating. That is all we can tell you. As for a motor rated same or less amperage as your drive which is normally run at 60hz you must ask your drive mfgr. What have they told you? If they are unwilling to tell you, then it would be nice to know their name so some of us can avoid them in the future. But I suspect you have not asked them yet. Have you?