Powerflex drives

DUNK · Aug 22, 2006

We have over 100 powerflex drives of different styles in this plant ranging from Flex4 to 700. We are having a problem with Mainly the 70's tripping out on over voltage. We do have about 1 or 2 Flex4's trip out every now and then with the same fault. Befor you ask we have asked our power company if they are having a problem on their end and they told us that they do have a capacitor bank that needs to be changed out and could be the problem. The question I need answered is is their a parameter in the drive that I am looking over that will prevent this fault? Its not happening with all the drives just a few.

TimWilborne · Aug 22, 2006

Can you give some details on the application that the drives that are tripping are in and are they on the same circuit? I wouldn't blame that power company that quickly.

Ken Roach · Aug 22, 2006

In my (limited) experience, overvoltage faults refer to the DC bus voltage inside the drive, rather than the incoming AC line voltage. The majority of these faults happen when the drive is trying to decelerate a load and the regenerative EMF gets put back into the DC bus of the drive.

This is usually due to either an undersized drive for the application, or a too-fast deceleration time.

First, try to figure out if the drive was decelerating when it faulted. If the drive is on a network, this should be easy to do using the Status word.

Next it's a question of the application. You could slow down the decleration, add a brake resistor module, or enable current limiting which will extend the deceleration when necessary to keep the bus voltage down.

LJBMatt · Aug 22, 2006

I've had customers with the same problem. They have high incoming line voltage (495 - 500VAC during weekends) that would trip out the drives on an overvoltage. What Ken says is true regenerative power on the DC bus back to the drive can cause overvoltage faults, so you would want to use dynamic braking or a brake resistor package. For the high line voltage the company ended up using isolation transformers to feed their drives to bleed off that extra voltage and that has cured their overvoltage issues.

DUNK · Aug 22, 2006

These drives are controlling rotary valves. These rotary valves are dispensing flour in flour lines at our silos. Hmmmm, maybe the decel is fast.. I will check the decel on the drives and see..

Thanks for the input!!

DUNK · Aug 22, 2006

I just checked the decel on the problem drives and they were 2 sec. I bumped them up to a 5 sec decel time. My next move is to wait..

Thanks again

DickDV · Aug 22, 2006

Dunk, the key piece of info on high bus faults is whether the fault occurs when the drive is idle or when the drive is running the motor.

If when running the motor, the problem almost always is regen energy from a rapid decel. If you can't lengthen the decel, you must add a snubber brake and chopper (the drive might already have the chopper)

If the fault occurs during idle times, the problem is the power supply. If can be extremely fast noise pulses and not a generally high AC line voltage. I would cure this by first adding 3% line reactors in the power leads. If the problem persists, add the same snubber prake package as above. It will work with the reactors to swamp the overvoltage when the power line gets noisy.

JohnW · Aug 23, 2006

Sounds like a problem with harmonics, if the power company capacitors are on your side of the transformer then the harmonics from your drives has probably damaged them. The line reactors that DickDV suggests should go some way to reducing the harmonics. It may be as well to carry out a harmonic survey.

russrmartin · Aug 23, 2006

Bus Voltage is your problem

The Overvoltage fault is due to bus voltage, and does occur when the load is in deceleration. You were correct in bumping up the decel time, but you may have to go longer. If the problem persists, you may have to install a dynamic brake. This is listed in the manual, and the two suggested remedies are what is mentioned above.

JesperMP · Aug 23, 2006

As others have suggested, the trips may be caused by regen during decelleration.

However there is another possible cause, and that is regen caused by the load being a large oscillating mass. In this case there can be regen for each rotation of the drive motor.
The difference is that it can happen during run at constant speed, not just during decelleration.

The remedy is the same, chopper + brake resistor.
Be warned that the brake resistor may have to be much larger than if regen just happens for the short time during decelleration.

mellis · Aug 23, 2006

Dunk,

Another possible choice...

If your application will allow it, you can switch your stop mode to "coast" instead of ramped. Then you don't have to guess about "how fast is too fast". I've had the same issue pop up on drives for pumps. The "ramped" stop mode just happened to be the default setting and was not needed. I think your rotary valves would be a similar situation.

JohnW · Aug 25, 2006

What is the fault code and what type of final gearing does the valve have?

Ken Roach · Aug 25, 2006

Any chance that these drives are networked to a PLC ?

It might be helpful to allow your PLC to babysit the drives for a while, so it could tell you what certain values are (incoming AC voltage, DC Bus voltage, stopping versus faulting, etc) when the fault happens.

Powerflex drives

DUNK

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