VFD Fault need ideas
VFD Fault need ideas
(OP)
I have a VFD (AB Power Flex 70) operating a 5 hp motor controlling a progressive cavity pump pumping starch material. The system is set up to pump the material for a time then flush for a time after material is used from tank system cycles again to fill the storage tank. This system has been in service for several years without problems and no changes have been made. Several months ago the drive started kicking out on Fault 24 (following is from manual)- Description: Decel Inhibit-The Drive is following a commanded deceleration because it is attempting to limit bus voltage. Action: 1. verify input voltage is within drive spec limits. 2.verify system ground impedance follows proper grounding techniques. 3. Disable bus voltage regulation and or add dynamic brake resistor and/or extend deceleration time.
Changed the pump and had no problems for about 6 weeks. The problem has returned intermit. Increased the Deceleration rate in the drive from 3 seconds to 4 seconds, thought this help but after 3 days the intermit problem returned. Monitored incoming 480vac for 24 hours, looked ok however during this time the unit operated ok.
Any ideas would be appreciated.
Changed the pump and had no problems for about 6 weeks. The problem has returned intermit. Increased the Deceleration rate in the drive from 3 seconds to 4 seconds, thought this help but after 3 days the intermit problem returned. Monitored incoming 480vac for 24 hours, looked ok however during this time the unit operated ok.
Any ideas would be appreciated.





RE: VFD Fault need ideas
It your power is grounded wye, then the power is probably not the problem. Consider the other issues the manual mentions.
RE: VFD Fault need ideas
Keith Cress
kcress - http://www.flaminsystems.com
RE: VFD Fault need ideas
No other machines have been installed and we generate our own power. The utility plant has added 2 new turbines to increase cap. and sell power to the grid just about the time this problem started. I am not sure how to try to tie the problem to the new turbines. I know of no other operating or power issues in the plant. Thanks for the replies.
RE: VFD Fault need ideas
Q? What is fault 24 and why is it not in my manual?
A! Fault 24 is the "Decel Inhibit Fault." This fault was not listed in the first manuals printed for the PowerFlex 70 drive, but are printed in the current circulation manuals.
This means that the drive is not following the commanded deceleration because it is attempting to limit bus voltage. You will want to verify that the input voltage is within the drive's limits. Verify the system ground impedance follows proper grounding techniques. Disable the bus regulation and/or add dynamic brake resistors and/or extend deceleration time. Parameter 238 bit 6 is the location to turn this fault on or off. By factory defaults this bit is on. Parameter 161, 162 and 160 are the bus regultation parameters that can be adjusted for application if the bus regulation is desired
RE: VFD Fault need ideas
It sounds to me that the VFD is trying to brake the motor and pump to a stop and the energy it is removing from the motor is over-charging the capacitors in the VFD. Try increasing the decel time further. You could also set the VFD to allow the motor to coast to a stop.
RE: VFD Fault need ideas
LionelHutz I agree, the reason I increased the Decel from 3 seconds to 4 sec (maybe I should go more). I cannot figure out why it goes for days without issue then back to back cycles it faults. The Operators run it in auto, I verified by watching it when it happen and the material (starch) is always the same.
Power is the other variable that I think is out there. I left a Fluke Meter on record on incoming A & B and was able to catch a fault the min.=475vac & max.=481vac. It has operated without problems for 24 hours and before that it faulted on 4 back to back cycles (about 1 cycle every 90min.) Measuring each phase to ground A=265vac, B=285vac, C=286vac.
RE: VFD Fault need ideas
It sounds like perhaps the new generation added may be keeping the mains higher which means the DC link is sitting higher. So when your drive goes into decel there is less headroom on the DC link capacitor bank to store the regenerative energy.
If coasting to a stop is an issue you can go with adding a braking resistor. Since you almost don't need one, it could be pretty small, power wise.
Keith Cress
kcress - http://www.flaminsystems.com
RE: VFD Fault need ideas
RE: VFD Fault need ideas
Is it possible you have an intermittent fault (loose connection) in the drives speed setpoint so it tries to go from normal to zero in no time flat which causes the code 24?
Roy
RE: VFD Fault need ideas
Thanks.
RE: VFD Fault need ideas
As far as the motor/load is concerned, if it stops in a few seconds then ok-it has no effect on the VFD, or it could take minutes to stop if the inertia is high and there is no friction (e.g. fans). Either way, the VFD would not 'see' it.
RE: VFD Fault need ideas
RE: VFD Fault need ideas
Do you think someone fat fingered a default parameter to other than default? I have had so many problems at customer sites before where this was the issue.
Do you have a list of parameters? I know this drive has hundreds. Do you have a list of parameters to compare it with todays list?
Maybe default it then change the parameters that need to change from default.
RE: VFD Fault need ideas
You might need to connect some high speed recording equipment to see what's happening. There could be sub-cycle transients that are causing the trip. A VFD fed with 3-phase power has 6 charging peaks per cycle. You only need a transient which boosts 1 or 2 of these peaks to cause the trip you see. A Fluke meter would never record this type of problem. I believe the Fluke use is 100mS averaging which is 5 or 6 cycles. Way too slow.
Do you have any capacitors around this VFD? Do you have any contactors switching the line power near this VFD? Is there a line reactor on the VFD?
RE: VFD Fault need ideas
I would immediately install a 5% line reactor ahead of the drive. It's not an expensive device and would be good protection for other power-related problems too. If the problem persists after that, a more detailed study might be in order.
As to a progressive cavity pump "motoring", I don't think so. That's about inconceivable due to their construction.
RE: VFD Fault need ideas
RE: VFD Fault need ideas
The VFD controls deceleration to a set time, the time programmed. If this is too quick then you will possibly get a level of regeneration. If you need a controlled stop, try a coast stop first and see how long it takes to come to a stop from 60Hz (or 50Hz depending on where you are in the world) and this will give a rough guide as to the decel time.
Alternatively, just increase the decel time to something like 10 secs (if your process can cope with this) or more and see if you get an alarm.
Maybe I'm a little too long in this industry but when companies make a point of highlighting a specific alarm or fault, it is often a 'problem' fault. FAQ's are often a subtle way of saying this is a bug but we don't want to call it a bug so we'll call it an FAQ.
RE: VFD Fault need ideas
He has already stated that he has extended the decel time out with no relief and went to Coast to Stop with no relief so there is near zero chance of the pump motoring on decel.
I'd say that motoring of the pump is not the cause of his faults. The next most likely cause would be input power transients, it seems to me.
RE: VFD Fault need ideas
Keith Cress
kcress - http://www.flaminsystems.com
RE: VFD Fault need ideas
No caps. or inductive switching around device.
DickDv I agree. I looked at the pump first then I posted for help and I temp. installed a iso. transformer 480-480 ahead of the drive yesterday when I posted the "follow up" post. It has been about 18 hours and no issues. I will report the findings when enough time passes to see a good or bad result. Thanks for all on this site I work for a small company without allot of Staff to discuss problems with. This site fills that gap.
RE: VFD Fault need ideas
RE: VFD Fault need ideas
Thanks for the come back, we all learn. Congrats.
Keith Cress
kcress - http://www.flaminsystems.com