Attention AB drive Guys

I posted this question a few months back but did not get the answer and it could be that the answer is not out there. But here it goes.

I have a PowerFlex 4 that is used for the lift/lower and travel for a bridge crane. It uses a contactors to send voltage to either the travel or the lift motor. Now to the problem.

Very intermittent problem (maybe once a month) where the VFD faults out for an I/O comms fault and right after (less than a second) for a HW overcurrent fault. It is always in that order when I look in the fault query. I have changed out the entire drive including the I/O card. I have changed out the cable from the PLC to the VFD and ensured that it is shielded right. There are two other drives on both sides of the problem drive neither of these have ever had a problem. I have monitored where the hoist is at at the time of the fault and there is no pattern.

The PLC uses the 24VDC from the drive to a relay output card for fwd reverse stop ect. Is it possable that I could somehow be inducing a spike from the relay output card into the VFD causing this? It uses an analog card for the speed referance.

I have called my vendor for AB and they are stumped.

Any idea's???
Thanks

Why are you using contactors with the Drive? You shouldn't need to and doing so could be part of your issue, depending on where the contactor is (electrically) in your setup. Does the contactor have an aux contact that has anything to do with the drives run controls?

I don't work for AB but, in general, it is asking for trouble to put contactors in the motor leads of a drive. In this case it seems that the idea is to use one drive to operated two different motors with the contactor selecting which one is under control.

I assume that the two drives adjacent to the problem drive are operating one motor only and do not have the contactor.

First, I would be sure you have a suppressor network on the contactor coil to minimize ringing and kickback spikes.

Second, I would arrange the controls so the contactor can only be cycled when the drive is Run Inhibited.

If the faulting can't be eliminated, I would review carefully the safety aspects of doing an immediate automatic fault reset. If there are no safety issues with auto reset, I would set the drive up for immediate reset and the operator will probably never know the fault occurred. I emphasize---safety issues must be reviewed first before considering this.

Ok I will clear a few things up for everyone.

You are right that the VFD drives 2 motors. The two other drives do the same thing. This is on an Automated Electro-Plating line. The line has three hoists. I have this same set up on another line that has been in operation for 4 years without any issues.

As far as reseting the fault we have a fault reset tied to the Wonderware HMI. This will not reset the fault. Pressing the stop button / reset on the drive does nothing. The only way to clear the fault is to power down the drive.

Yes the contactors come on a split second before the enable for the VFD and the VFD drops out a split second before the contactors release.

What fault # are you getting? Your original post said the problem was on a "70", this post said a "4". I assume you've amped your motor(s)?

Sorry it is on a 70. It is fault 121. Followed by a HW Overcurrent fault. In that order each time.

I had been reading some stuff on powerflex 4 and 40's got my # mixed up.

Do a megger check on your cables from VFD and also to the 2 motors
and ....if the the problem still continues and the VFD are the same chenge them between to see if the problem is transfered....

Regenerative?

Just a thought that occurred to me. But take this with a big grain of salt, I am still learning this great field.

Are the motors themselves fully stopped before you open the contactor? Is there a chance the other one may still be spinning, flywheel induced, when you pull that one in?

One of these conditions may allow a spike back onto the drive which it does not like.

I like the PowerFlex family but they do not seem as hardy as the 1336 Family and prior.

Both Motors are SEW Eurodrive motors they have a brake on them so that when the power is gone the motor is stopped right away.

WAG: The I/O fault happens first. The drive tries to stop the load (ramp or coast?). At what point is the brake de-energized (engaged)? Could the brake on this particular motor be causing the overcurrent fault? Take a close look at how the drive fault contact is wired, and the brake coil.

Another WAG, if your I/O cable is "bruised", and intermittently shorting causing the I/O fault, the drive may be attempting an immediate stop while the contactor is opening which could lead to the overcurrent fault. Does this drive have the fail safe jumper option? If the drive fault contact opens, will that cause the contactors to open immediately?
I use contactors after the drives as a general practice on all types of AC drives. Yes, it's true that can cause faults if the contactor fails or the drive attempts to run during contactor closing or opening, but with careful wiring and programming of the drive and controls, they are trouble free and provide hardwired safety. Timing is everything, and it's easy to overlook a condition that may cause faulting. DickDVs suggestion for setting up the auto reset feature will get you up and running the fastest, but like he said, make sure there are safety issues before doing that.

mrdmrd said:

Sorry it is on a 70. It is fault 121. Followed by a HW Overcurrent fault. In that order each time.

I had been reading some stuff on powerflex 4 and 40's got my # mixed up.

Click to expand...

There is no fault 121 listed in the Flex 70 manual so has AB told you what it is? OR did you mean Fault 12 which is HW Overcurrent?

Since you have 2 machines that are identical I hope you verified the parameter settings are identical and the programming...ie when the contactors open/close are timed/done the same.

The manual offers the obvious; Check programming. Check for excess load, improper DC boost setting, DC brake volts set too high or other causes of excess current.

Another aspect could be the electro-mechanical brake, if that is what you have, could be binding or not properly adjusted which could cause an overcurrent if not released properly.

A little extra programming could be done to determine at what point the fault is occuring.

If you have 2 systems that are identical and one does not offer any problems then I would look for what is different, has to be something even if its just a loose wire.

The manual; http://literature.rockwellautomation.com/idc/groups/literature/documents/um/20a-um001_-en-p.pdf

Maybe they left it out of the PF70 manual too:

http://domino.automation.rockwell.com/applications/kb/RAKB.nsf/0/043432341227F54985256B73006F707A?OpenDocument

Is The I\o Cable Shilded? Is It Ruted Together With Power Cable?

Make sure you have programmed and are using the drive "Running" bit back from the drive. This bit will remain on as long as the motor is being turned. Make sure the brake does not engage until the running bit is off (motor stopped) Also make sure the contactor cannot swap motors until the drive running bit is off.
I have run accross a few installations where the drive start bit was being used to control a brake. This would not allow the motor to ramp down because the brake was engaging before the drive decelerated down to zero/stopped. This resulted in infrequent OL's.

Ok everyone I found out that I don't know what I am talking about.

Here are the facts

Hardware PowerFlex 700

Faults
HW OverCurrent 12 The drive output current has exceeded the hardware current limit. Check programming. Check for excess load, improper DC boost setting, DC brake volts set too high or other causes of excess current.

I/O Comm Loss 121 I/O Board lost communications with the Main Control Board. Check connector. Check for induced noise. Replace I/O board or Main Control Board.​

According to the fault queue they always happen fault 121 then fault 12.​

What I have done so far:​

Replaced the drive with one that I removed from a line in working condition the day previous to the swap.​

Replaced the Cable that runs from the PLC to the I/O board. Ran it outside of the wire duct to ensure nothing was being induced.​

Made sure that the proper shielding was in place on the cable.​

Checked all perameters with the two other drives on this line which are setup to perform the same functions as the problem drive also checked setting against another line that is a twin to the one with the problems. All perameters are the same for all six drives.​

Checked all wire connections all are tight.​

Took amp reading from each motor. All well within specifications.​

I have not done the following:​

Replaced the cable for the analog speed referance signal from the PLC to the VFD.​

Dropped a granade in the control cabinet and slammed the door (but getting closer every day.)​

Other information:​

Drive uses a coast to stop because of the mechanical brake on the Eurodrive motors. As each hoist approches it's target station the hoist slows down to a crawl so that the brake does not slam on at full speed.​

Same drive runs 2 motors, never at the same time. One is for the lift and one is for the travel. Two contactors decide which motor get the power from the VFD.​

The only way to clear the fault is to power down the drive. I think this is because of the I/O comms fault. It has to re-establish communication with the I/O board.​

Thanks to everyone that has givin input to this problem.​