Capacitor Bank Damaged by VSD Harmonic

First off you don't know for sure that the small inverter loading is what damaged the capacitors. I'm not saying it didn't, I'm just pointing out that just because they were the only things connected does not automatically mean they are the cause.

That said, high harmonic currents can cause the capacitors to over heat and swell, eventually causing the breakdown of the electrolyte. The is one of the main reasons why I never recommend bulk PF capacitor correction or even automatic PF correction systems such as what you described. EVERY one I have ever worked on or with has had a catastrophic failure like this. Those systems were designed in an age when VFDs and SMPS based ballasts were unheard of. Resonance problems now make automatic PF correction systems a very risky endeavor in my opinion.

What can you do? Investigate thoroughly to determine if the damage was caused by a resonant harmonic situation or a surge/ spike on the line. If it was harmonic related, find the crucial harmonic and design a de-tuning reactor and/or filter into your system to avoid that problem in the future.

Thank you very much JRaef for your answering my question.

I have 2 unit of similar 4000A main switch board with same spec , the other connected to 200 Ampere loads except some lighting and air conditioners.The capacitor bank is work good.

Thank you and Regards