Intermittant Drive trips

We have an application using Siemens MM430 200hp drives running variable-speed water pumps. The pumps maintain level in a hotwell, 1 drive running at a time. A drive will run for up to 9 days at a time and then fault, normally on overvoltage. We have line reactors installed (before we installed them the drives would trip every 2-3 days instead of every week.) The load side cables are around 100 feet long, which would seem short enough not to require load reactors, but could I be wrong on this?

Ramp times are about 15 seconds to full speed up and down, and the drive ranges from about 38-42 hz, this over the course of 5-10 minutes. All the parameters in the drive use the exact data from the motor nameplate. We have 3 drives and they are all set up the same, and all acting the same.

We took out the voltage boosting functions to try and combat this, to no avail. Does anyone have other ideas we could consider?

Water Boy

Just an idea. Are you by any chance removing the run command then trying to restart the pump before the drive finishes it's ramp down?
This scenario can cause overvolt faults. We programmed our logic to remove a run command and not allow the pump to be turned back on until the ramp down time has expired and it prevented all overvolt faults.

No, the drives run more or less continuously (except when they trip!). There is no automatic stopping of the pumps unless a low level condition exists, which is not happening.

When we had pump issues we used to document all parameters in the system to see if there was a pattern or recurring symptom. We had levels, flows and pressures to maintain so we built in preventative logic and diagnostics.
You might see if you get air in the line, or intermittent sensor that requires debounce control. It's kind of hard to say it's the drive's fault without being there.

It could be a loose connection on the outlet side of the VFD. A loose connection will generate archs that will appear as overvoltage to the drive.
It is the same that happens if the drive is disconnected on the outlet side when loaded (I have tried that and it generated an overvoltage alarm on the drive).

We just got the Simatic Drives software package, which we're going to use to monitor a bunch of the parameters in the drive to try and isolate this a little better. Our feeling right now is that it's a rogue parameter somewhere in the drives which we haven't found yet... we just installed these in January and we're not terribly familiar with the Siemens Micromasters yet. The only external signal to the drive is the speed command to it, which is a PID loop running off of a bubbler. The PID loop settings never change.

Our power line is also suspect, but I would think that the line reactors should have taken care of that. We did put a data logger on the incoming line for about a week and weren't able to find anything substantial.

Jesper- I would suspect a loose connection if it were only one of the drives doing it, but it occurs on all three.

In general, after I have eliminated the electrical faults and power quality problems the other guys have identified, I suspect that the acceleration and deceleration times are not long enough.

A 200 hp centrifugal pump constitutes a significant inertia resisting the drive and motor changing speed. This can be exagerated by the effect of the water flow trying to make the pump into a turbine.

Generally, if the drive is tripping out on overvoltage it is a result of the decelleration time being too short and the load inertia generating back EMF. Generally, if the drive is tripping out on accelleration you will get an overcurrent trip. DickDV can shed additional light on this.

Try extending your deceleration time by 25% to 30%. You can't be too far off the mark because your trips are intermittent. Slight change in backpressure or flow rate may be making the difference between riding through the speed change and tripping out. Note that if you change your acceleration and decelleration times you may have to tweak the tuning on the PID loop a little!

We had some much smaller drives that were tripping out with overvolt. Turned out to be a grounded leg in a heating unit on our roof. I am assuming that you monitor such conditions with size units that you have, but it is a thought.

I tend to support Tom Idea change you ACC and DCC in one of the drives and see if you have any change.

Thanks Tom and Arik, I'll try that... of course, it's likely to be a week or more before I know if it worked but I'll keep you posted.

Lots of good suggestions above. If I were to list them in order of trying them, I would start by doubling the decel time on only one drive. See if it continues to run the next time the other two trip.

If the drive is doing the PID control, you may have to limit the speed slew rate in the output of the setpoint controller. Hopefully, the drive has the capability to do this.

Being a European drive, it most likely has an EMC filter that only operates properly on a properly balanced AC supply. US ungrounded delta power sources drive these systems nuts when they encounter significant imbalance, worst case being operation with one leg grounded. On the drives I am familiar with, imbalance causes the drive to fault on DC Bus Overvoltage. The solution, short of changing the nature of the power supply, is to disconnect this EMC filter network. Hopefully, the drive mfgr has provided instructions on how to do this.

Motor lead lengths and reactors or not in the motor leads are not a likely source of this fault.

Finally, JesperMP, you say you have pulled the motor leads open while loaded?!!! HOLY COW, MAN! THAT'S A GOOD WAY TO BURN ALL THE HAIR OFF YOUR HANDS, FACE, AND HEAD OR A LOT WORSE!!!!! Opening loaded motor leads lead to a huge flash which highly resembles being hit by lightning. Anyone considering doing this, JUST DON'T!!!

Dick,
you are right, but I didnt open the leads manually, it was the emergency stop system that at first I thought that it was most important to shut the system down immediately (with the disconnect in the outlet of the VFD).
Normally the circuit would allways be engaged, tripping only when a safety was violated. I soon changed my mind and switched the disconnect to the inlet side of the VFD.
The downer with this is that my network connection to the drive will also be zapped when it happens, but it must be this way I guess.

In some cases, it's allowable to place a contactor between the VFD and motor, but you want to remove the ENABLE on the drive before opening the contactor.

Otherwise you can get the spectacular display Dick mentions... :nodi:

beerchug

-Eric

Right, I did experiment with a timedelay between stopping the drive and opening the contactor. But when the E-stop is activated there cant be a timedelay.
Also, the E-stop can be activated any time, for example at the most severe moment, when the drive is accellerating or decellerating.
So it can be a gamble to put the contactor after the VFD, and I dont want to risk anything.

By the way, all modern VFDs that I have tried generate their control voltage from the mains. So when you cut the mains, it dies completely.
In the old days there was a separate supply to the control, but that seems to be out of fashion.

All of this doesnt help Water boy much of course.

A contactor in the motor leads is OK because it is designed to handle the flash. I prefer to see a pre-action switch on a motor lead disconnect to interrupt the drive enable circuit also.

Most modern drives can tolerate a contactor opening in the motor leads without damage but, if the contactor is reclosed with the motor standing still, you almost always will get an overcurrent trip.