I have a Powerflex700S 480V drive running a 350hp motor connected to a process fan. I appears that every once in a while (mostly at night for some reason) the drive trips on an instantaneous trip.
When looking at this paramater it states that this trip occurs when the motor current reaches 214% of full load current. Full load current is 392A so the drive must see 838A in order to trip on this fault.
Our DCS does not show any increased current or any trend upward in the current before it trips. Even if there was an upward trend due to process conditons or something the drive would hit its "overload" or "overcurrent' fault before the instantaneous, is that correct?
I have put a power meter on the drive output to watch and see if I can recordd any transients, since our DCS may not be quick enough. My question is what on a fan can cause the current to be driven so high so quickly that it causes an instantaneous fault? The only thing I can think of is some of intermittent cable or motor fault? The system is ungrounded (zig-zag xfmr for ground detection) so this pretty much rules out any ground fault current.
Is it possible that the drive is being fooled into thinking there is this much current for some reason? Noise, harmonics, etc..?