DC Bus Overvoltage Faults are usually caused by motor regeneration/braking.
Symptom 1-
" Lets temporarily ignore this statement because this is an assumption. Not a bad one but a guess nonetheless. I saw no evidence, yet, that indicated there was a utility/supply problem.
My biggest question is this: When you command the VFDs to STOP, do the fans need to come to a quick and controlled stop (braking) or can they simply coast to a stop (like most fans do)?
If there is no need to BRAKE the fans then you need to set the "Stop Mode" VFD parameter to "Coast to Stop". There is no reason for it to be anything else.
Next I would definitely set the "Flying Start" parameter to "Enabled". No reason for it to be off. No reason for the VFD to care whether its stopped or spinning before it restarts. (on a fan)
Symptom 2:
-If there is ANY slight blip in power. Usually occurs when its windy, these VFD's are the first to trip but everything else stays running."
This says that the wind is trying to move the fans faster or slower then the VFD is commanding them to go.
If the wind tries to slow the fan down the VFD applies more power and spins the fans back up to speed: No problem there.
If the wind tries to speed the fan up then the VDF must SLOW or BRAKE the fan: This is the PROBLEM.
When BRAKING the VFD must dissipate the extra energy. This is dissipated as heat (on the vfds in question). The VFD can only dissipate so much past which the DC Bus voltage rises.
For symptom #2 you need braking resistors. They will dissipate the extra energy that the VFD alone cannot currently handle when slowing a high inertia load.[/QUOTE]
I don't disagree with most of what you said, but I also will give credit to the OP that he likely knows there is incoming power supply problems occurring. This could easily be observed by light flicker, or other loads cycling, or electrically held control circuits dropping out. If the tripping VFD's were the only symptom, he may be asking his question a little differently if he doesn't know there is a problem with incoming power.
I also don't disagree with your theory of the wind speeding up/slowing down the fan, but have to question just how likely this is to happen on a severe enough level that it trips the drive. What is a windy day? Some places that may mean anything over 10 mph winds. Other places though they do have calm days, 10 mph is pretty usual and not considered "windy". Some even get 25 mph winds and may consider that to be somewhat normal, but do acknowledge it is not calm winds either. Something tells me these fans need to see at least 20-25 mph gusts before it will have much impact on the drive's ability to maintain output speed, particularly when it is trying to increase fan speed and even then it needs to hit the fan from the right direction - nearly straight into the fan inlet, or it will not have such direct impact.
If the wind is blowing POCO lines get to swinging around and eventually connections do loosen up and can easily cause the kind of blips the OP is discussing. Most of routine maintenance by rural power companies is repairing things damaged by wind, most of it just things that happen over time. Go out on some of the days we have had the past couple months with the wind blowing over 30 mph and watch those lines whip around and it is amazing they don't fail more often than they do.
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This says that the wind is trying to move the fans faster or slower then the VFD is commanding them to go.
