Powerflex 70 not faulting during power sag

[fiveliter8]

Good day everyone! We have several laminar flow hood blowers controlled using powerflex 70 drives that are tied into our building management system (siemens). Our BMS is programmed to attempt re-start of the drives if it sees both a fault and not running output from the drives. When we get a power outage, all drives restart as they should by our BMS once power is restored. We also receive periodic power sags that last shorter than one second, and when this ocurrs, the drives drop output to the blowers, latch a not running output (which BMS recognizes) but never faults. We can re-create the situation manually with the mains disconnect. What we found is as long as the display on the drive remains on from residual power after mains is lost, and then mains is restored, the drives behave the same way as during power sags. On our equipment that use powerflex 700 drives, we don't have this issue. Looking at the manual for the drive, it would seem the undervoltage limit is hard-set and not adjustable, as we don't see a parameter to adjust this. Is there something we are missing? Our controls engineer is dead set against modifying the BMS program to attempt restart without the fault signal from the drive (and all the red tape that goes along with it). Is this an inherent issue with the 70 and we are stuck with manual restarts after sags?

 

[crawler009]

Hello fiveliter8,

we had a similar problem with the PF70, but our Problem was
that it went to a Fault, without reseting its fault when the power
was restored after 2 - 5, before the inverter could turn off
completely.


Do you have the autoreset for fault on?

In Parameter -> Utily -> Faults -> Fault config 1
(Parameter 238)
you can set the fault sources.
Try to disable all Fault sources, except Motor OverLd
and HSLow Temp, and then see what the drive does.

Best regards,
crawler009


Edit: Or maybe its the parameter (168) Start At PowerUp that should be 1.
Check the parameters 168 - 175.

 

[fiveliter8]

Thank you for the recommendations. Will give them a try!

 

[OkiePC]

I would be very careful about turning off any fault config bits. I would also be careful about restart on power up although I believe that is going to be your best solution. It sounds like your drive logic shuts off and then is restored while the BMS is holding the run signal high. So the drive by default needs a false to true transition of this signal, but otherwise is not faulted. The fault relay should have changed states at least briefly if this is what is going on with the drive.

If you alter the power up behavior, just test the system to see if something is different in all modes, and make every one aware, attach any required signage, etc.

I am being overly cautious, I know it is a fan, inside some huge housing with 90 bolts, right? Anyway I also like to use the fault autoreset timer and retries counters occasionally. In most cases, if you try to reset a fault 3 times with a 2 second delay between each attempt, a person should not be able to get into the danger zone in 6 second assuming it is guarded. If it was a one off overload it may restart just fine, or a nuisance fault due to a power disturbance or other, the autoreset fault settings can be a real time saver. If it is a real fault (usually mechanical overload) you are not going to do much harm in 3 tries, if it'stuck, it will go ahead and fail.

 

[fiveliter8]

Update - issue resolved

All,

Just wanted to post an update.

The digital input for the run signal (parameter 362) needed to be changed from a 7 (run) to a 43 (run level).
During a power sag or blip, we momentarily lose the enable signal to the drive (we learned of the display 'last stop source' parameter from rockwell). Once the enable signal is active again, the drive looks for a run input. When the run input parameter is set for 7 the drive is looking for the run input to transition from off to on before it will restart. Since the run signal stays active, the drive does not see a transition and will not restart until the run command is cycled. If the input parameter is set for 43, it does not require a transition and only looks for the input to be active before it will restart.
The drive does not fault during any of this, so the BMS logic to attempt restart is never executed. We have tested this and all is now good! Thanks for all the insight and assistance!

Alex