Powerflex 755 Fault 5 Overvoltage

Hi all - -

Looking for advice on what to look for hopefully, I am not a drive guy. Off site today and don't have anything in front of me, but here is the details I can recall at the moment:

New installation, however this line is identical to others in the factory, and also this is the first time factory has used 755. Has been 70's and 700 and a few 525 sprinkled in of the other lines. This line is all 755, roughly 30 or 35 VFDs. Most of the application is on pumps, some Axiflow screw, some centrifugal, a couple Positive Displacement, etc. All Ethernet. We set all drives for HD instead of normal. All the drives have their blue donuts filters installed, can't think of the name of them at the moment.

Two drives are giving us a Fault 5, over voltage on the DC bus. The first one (30HP) is a centrifugal pump on a closed water system. At 60 Hz, is when we see the fault, and it will only run at full speed for about a minute. At lower speeds it will run ok. The second drive (150HP) is on a homogenizer. We see the fault when the line is ramping down, around 35 to 40 Hz. It is fairly consistent at the same moment when it faults.

We rely on the CCW startup wizard to help us setup drives. Again it is not in front of me, but in general we set the motor data obviously, calc the motor poles to the rpm (most stay at 4), disable reverse, set accel and deccel 5 to 10 seconds depending on pump, sensor less vector, disable breaking, set to coast (factory uses this to try to recover from brown outs if possible) set the comm port for speed ref, set most pumps for 6 to 60 Hz. I can't think of other settings at the moment, but most things we leave to defaults or disable.

Just looking to see if someone might know something to look for or have experienced this before and by chance say "go set parameter x to y!"

One of the questions is because the 755 handles a lot of applications for motion and whatnot, are there parameters the CCW startup wizard doesn't cover that we should be aware of?

We started a case with RA on the smaller VFD before the big guy starting showing the signs. We may try to get the local RA office to send in their drive guy, just wanted to see if we could try a couple ideas on Monday!

Thank you all for your time and any thoughts.

mort81 said:

Hi all - -

Looking for advice on what to look for hopefully, I am not a drive guy. Off site today and don't have anything in front of me, but here is the details I can recall at the moment:

New installation, however this line is identical to others in the factory, and also this is the first time factory has used 755. Has been 70's and 700 and a few 525 sprinkled in of the other lines. This line is all 755, roughly 30 or 35 VFDs. Most of the application is on pumps, some Axiflow screw, some centrifugal, a couple Positive Displacement, etc. All Ethernet. We set all drives for HD instead of normal. All the drives have their blue donuts filters installed, can't think of the name of them at the moment.

Two drives are giving us a Fault 5, over voltage on the DC bus. The first one (30HP) is a centrifugal pump on a closed water system. At 60 Hz, is when we see the fault, and it will only run at full speed for about a minute. At lower speeds it will run ok. The second drive (150HP) is on a homogenizer. We see the fault when the line is ramping down, around 35 to 40 Hz. It is fairly consistent at the same moment when it faults.

We rely on the CCW startup wizard to help us setup drives. Again it is not in front of me, but in general we set the motor data obviously, calc the motor poles to the rpm (most stay at 4), disable reverse, set accel and deccel 5 to 10 seconds depending on pump, sensor less vector, disable breaking, set to coast (factory uses this to try to recover from brown outs if possible) set the comm port for speed ref, set most pumps for 6 to 60 Hz. I can't think of other settings at the moment, but most things we leave to defaults or disable.

Just looking to see if someone might know something to look for or have experienced this before and by chance say "go set parameter x to y!"

One of the questions is because the 755 handles a lot of applications for motion and whatnot, are there parameters the CCW startup wizard doesn't cover that we should be aware of?

We started a case with RA on the smaller VFD before the big guy starting showing the signs. We may try to get the local RA office to send in their drive guy, just wanted to see if we could try a couple ideas on Monday!

Thank you all for your time and any thoughts.

Click to expand...

Have you considered Line Reactors on the supply side?
Have you considered Dynamic Braking?
IF the drive ever trips, while not running, just sitting there powered up, on Over Voltage, this is most always the fault of the supply system. You might only see it on Monday morning, before the rest of the plant is fully running. Or, other times. MOST typically, other VFD with the same supply will also have this fault, but you do say that this is the first 755 (the only one?), so perhaps small differences????

The centrifugal Pump that trips on speed change is easy. There is something about the hydraulics in that specific system that is allowing more siphon action on that pump than others, so at the short decel ramp time, your motor frequency coming from the drive is lower than the actual pump speed, turning your motor into a generator and putting DC energy into the bus with nowhere to go. For that one, you need to simply experiment with lengthening the decel time to get rid of that situation. I would do so in increments of 2 to 3 seconds.

The other one that is tripping only at steady state full speed and at no other time is trickier. If there is a valve in the system that is also trying to control flow even though there is the VFD, or a powered check valve, that could create a similar situation as above, but in kind of the opposite manner. How that can happen is that the drive ramp up time is actually too LONG compared to the valve opening time so that when your valve goes to 100% open, but the VFD is not yet at 100% speed, the higher available flow allows siphoning and pulls liquid through the pump faster than it is wanting to via the VFD, again turning the motor into a generator. Remember, all the motor needs to become a generator is for the relative motor rotor frequency to be higher than the stator frequency, and all the VFD has control over is the stator frequency. So any time the VFD commanded frequency is lower than what the load pulls the rotor (in this case siphoning liquid), kinetic energy in the system is converted to electricity that goes into the DC bus.

If playing with the accel/decel times doesn’t cure that, it may be some other source of resonance in the power system, ie PFC capacitors on some other machine or an adjacent regenerative drive or something. That’s going to be harder to find and more expensive to fix, so try the free stuff first. Lengthen the decel time on the one that trips on decel, shorten the accel time on the one that trips at full speed.

Specific to the 755 there is also a parameter for turning on and off what’s called “DC Bus Regulation” which might also help, especially on the steady state one. But that often comes with other side effects that the AB Tech Support people can discuss with you, which is why I mention it last.

Try changing parameter 53 motor control from 0 (sensrls vector) to 2(custom V/hz) and see if this helps you out. Also auto tune the drive.