I've had the exact same problem twice in the last two years and it has nothing to do with the equipment. What I could not figure out was why the problem occurred at the same time every day, or most days. Must have paid for couple of service calls before we figured out it was a problem with electrical service.
Contact your electrical utility service center and carefully explain the problem to a second or third level customer care agent, someone who knows the diffence between an amp an a dead cat. As them to put recorder on your transformer so they can document the service lapse and trace the problem up the local network or grid.
In my cases the two incidents (each incident lasting more than a week) had different causes but the result was the same. There was a momentary lapse in service which tripped the VFD. Reset the the VFD and you are back in busimess, but what if you aren't there?
