Plc S-300 issue

I,m a newbie engr, I have a plc operated feed plant here, where we faced some issues recently like sudden motors tripping although we had checked motor circuits and tested vfd (by this method) but everything was fine, overall plant tripping and erorr alarms.
First it indicated alarm of some supply issue so we tested incoming power supply, inverter and other things. So if anyone can guide me about this that what should i check and please refer some tutorial or plc guide.

What brand of VFD? What is the error code that the VFDs are giving on the faceplate?