VFD Faults
VFD Faults
(OP)
We are having problems with a VFD, at a Pump Station, having "HW Overcurrent Faults" after the weekly generator exercise event. The odd thing about the fault it does not happen when the weekly exercising of the generator occurs, but it happens approximately 3 to 6 hours, or more after the generator runs. There appears to be some connection between the VFD faulting and the generator weekly exercise, but all parties are at a loss as to what it may be. The generator is a Kohler 100KW/125kVa natural gas fired. The service is 277/480 volt 3 phase. The VFD is a Allen Bradley Power Flex 400 and it is used for a Pump Station with 2- 24.8 HP, 460 volt submersible pumps. Has anyone ever run across this time of problem before or have suggestions for possible causes of this problem.





RE: VFD Faults
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: VFD Faults
Has something reduced the pumps' working heads? More flow than in the past?
If the DC brake volts are adjusted too high or an improper DC boost setting can trigger that fault.
Any chance of the drive's room humidity rising dramatically after the generator has run?
Keith Cress
kcress - http://www.flaminsystems.com
RE: VFD Faults
That brings up this curious thing about your observation of it only being related to having been run from the generator 6 hours earlier. It's possible that this is coincidental, but it sounds as though you have observed it as a consistent event sequence. That raises more issues than it solves. I can't see it having anything to do with the VFD itself, although honestly, I kind of like Keith's idea on humidity. For example when the generator is exercised, the exhaust must be vented, so a lot more outside air is introduced to the room to replace it. Six hours later the pump station is being called for less duty and the VFDs shut down, cool off and the added room humidity condenses in and around the drives, current flows to ground and the drive is tripping on that current flow, or at least the sensors used to determine current flow are being shorted and giving a false signal. Remote, yes, but I think plausible.
So what else, if anything, is different about how it is run when in the testing of the generator takes place?
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: VFD Faults
RE: VFD Faults
RE: VFD Faults
If it is just the interruption then you could cause it without the generator at all. Maybe a longer dead time would help.
RE: VFD Faults
I'd be taking a close look at what happens in that pump station 6 hours after the generator shuts down. Sounds to me as though it might be something set on automatic, like maybe an engine block heater? Oil filter? A capacitor bank that is disabled while the generator is on and re-enabled 6 hours later? Battery charger?
Here's aanther issue though, are we assuming the VFD was actually running the pump when it faulted, or could it trip on HWOC while sitting idle?
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: VFD Faults
On a HW (high water) alarm,the pumping system normally starts the second pump. The second pump tries to start but may be spinning in the opposite direction due to first pump running and creating reverse flow down the second pump head if both pumps discharge into the same pipe or vessel. If that is the case, you need install or repair check valves at the pumps discharge or put the check valves at some other location on each of the pumps discharge lines and put an anti-backspin timer on each pump. It has been a few years since I have worked Power Flex drives, but I seem to remember there is such a timer in the drive setup.
ps: afterthoughts 1) Check all of the grd connections @ the service, drives, and pump motors.
2) Check you water level controls and wiring, such as floats, ect.
Hope this helps and good luck
Dave
RE: VFD Faults
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: VFD Faults
I most likely worked on at least 20 Power Flex Drives, which most were for pumps.
Dave
RE: VFD Faults
Any components that could manually or automatically isolate input or output of VFD might need further investigation.