DOL chnaged to PowerFlex 525 Issue

I'm having an issue with a PowerFlex 525 (25B-D043N114).

The set-up was as follows;

EXTARCT FAN 1 --->---|--- BOOST FAN --->
EXTRACT FAN 2 --->---|

Extract Fan 1, DOL, NP 18.5kW @ 400V @ 50Hz
Extract Fan 2, DOL, NP 18.5kW @ 400V @ 50Hz
Boost Fan, DOL, NP 22.0kW @ 415V @ 50Hz

The boost fan is used to compensate for losses in the ductwork from the extract fans so that the air stream gets to its destination. In this set-up when both extract fans are running the boost fan pulls around 20A per phase, with fan speed around 2000RPM. The boost fan when idle does freewheel at approx. 500RPM when the upstream equipment is running.

We then changed the boost fan from DOL to the PowerFlex VFD. The following parameters have been changed from default;

P31 = 415
P32 = 50
P33 = 41
P34 = 41
P35 = 4
P36 = 1480
P37 = 22
P39 = 1, also tried 0.
P41 = 30
P42 = 30
P43 = 0
P44 = 50
P45 = 1
P46 = 2
P47 = 2
T65 = 13
T76 = 2
T81 = 0
A545 = 0, also tried 1.

However when we run the boost fan it keeps faulting out on overload.
When the boost fan is turned on and the extract fans are off it pulls around 28A(read from VFD HMI). When you turn on one of the extract fans the current goes up to around 35-37A, when the second extract fan turns on the current is around 48A and the output frequency is reduced to around 47Hz, thus reducing RPM of the fan to around 1700RPM.

I am looking for advice as to what could be causing this and potential solutions to try. We installed a bypass arrangement in case the VFD failed so the boost fan is currently operating DOL.

Thanks in advance.

Are you sure you have the VFD putting out the correct phase rotation? Remember, if you determined the rotation when DOL, the VFD input doesn't reference that, so the output can be different even if wired visually the same. Simple enough to check, just tell the VFD to run the other direction from the keypad.

Thanks jraef. This was exactly the problem! That'll teach me to check things myself rather than taking someone else's word for it. Changed direction output terminal, now running ok.

I'll give you one guess as to how I thought to check that...

(Hint: you are not the first, nor the last person to have this happen to you, but chances are it will never happen again. )