ABB ACS550-U1

Sounds to me, and just guessing, that there is a air leak in the suction line causing loss of capacity, or failure in check valve causing loss of prime....could be crack somewhere...is there an air bleed on the pump discharge...?

When you say 1/10 the flow rate...what is the cause there? What does the VFD say the drive speed is?

Is there an unusual amount of cavitation (due to the change in pressure during stop/start conditions)? Do you have a way to monitor pressure at intake, pump housing and output?

I wish I knew the cause. Both VFDs appear to be running at reference speed from what I can tell.

Pumps are submerged well pumps with plenty of head, typically about 10'. There are check valves in discharge line from each pump to common header, but again, normally the system runs with no issues. Discharge pressure appears to be fine, but does respond to motor speed changes.

We've metered the hell out of the wiring; all appears to be as it should for voltages and currents in both 3 phase and single phase modes.

Are you sure this is an electrical problem? I would bypass the VFDs and use a clamp-on ammeter to ensure that both motors are drawing approximately the same current and receiving the same voltage. If ok then I would repeat with the VFDs in circuit.

If everything looks ok then it's time to monitor the pressure and flow from each pump under both conditions and compare. Do they feed a common header, are there any check valves, etc., maybe the foot-valve (if any) is stuck open, are they both at the same depth and/or near each other, there's a chance that the water table has receded below the higher pump.

One more electrical thing, are the motors rated for VFD service? If not there's a chance that the insulation and/or the starting capacitor (if there is one) may be failing prematurely due to the transients inherent in VFDs. If the VFDs were added a long time after the pumps were installed then you maybe facing imminent failure, maybe it's time to check the insulation resistance of your pump motor circuits.

Let us know what you find.

No, I'm not sure, except system works fine normally.

The submerged well pumps are about 50 feet apart and less than 100' from a natural lake. It's a municipal water supply. There are hydrostatic pressure transmitter in each well, and neither has shown less than 10' of head at any time in the 40' deep wells. The transmitters are mounted at same level as top of pump, so actual pump head is more like 12'.

Common header with check valves, so pumps should not be fighting each other. Line size is such that there is minimal backpressure on pumps even with both running full out.

Pumps are new as of summer 2013, while drives have been there for about three years.

Like I said, most of the time the system runs fine, it is only when power switches back from 230VAC 3 phase from generator to 230VAC single phase from utility do we see any issues.

Is it possible that this problem has been occurring since pump changeout and has gone unnoticed, or problem has definitely started just recently...? Is it possible that the pumps characteristics have been changed and is creating flow turbulence or cavitation...?

This problem only appears on return to normal power? How do you get it to run normally again once back on the utility feed?

As a qucik try... ramp the pumps up to full speed over 10 seconds or there abouts. I have seen a situation where one pump will deliver pressure before the other one... which raises the pressure in the header... so that the 2nd pump has to pump against that when starting.

The operators generally shut down the pumps, then turn them both back on, all from the PLC/HMI.

I thought it might be from one pump having to fight, but that wouldn't explain why our total flow rate is so low in this case.

Both pumps have a 30 second ramp up and 30 second ramp down configured. When power comes back on PLC, the first pump, the one having what appears to be limiting issues, starts, then the second pump (no issues), starts about 5 seconds afterwards.

I am impressed with the speed of your responses. It is a nice change. You should stick around after this issue has been addressed.

Damn, I should have thought of that! Great idea, I'll pass it onto the customer. I'd go myself, but it's 2-1/2 hours from our office to the site and it IS late Friday afternoon. :D

I think that is similar to what Kramarat meant in post #3, just worded better.

I think he suggested switching the leads from the ATS to the drives, which would not have accomplished anything.

But switching the leads from VFD to pumps? Now, that would be an interesting exercise, and useful.

North of 60: I just took a gander at your location on Google Earth. Mind my asking what you do? I'm just terminally curious, especially about folks in what I would consider an out-of-the-way location.

I will reply to you through CR4 private mail.

But the essential details are... I am a Chief Electrical Inspector for a Canadian jurisdiction.

I was just planting the seed of changing things around to pinpoint whether or not it was a pump problem or something else. A shot in the dark.

Northof60 nailed it.

Somebody knock down my GA. Anybody else with a similar problem should go directly to Nof60's post.

No need to remove the GA point, Your's was a valuable contribution.

That is one of the nicer things about CR4 if you ask me, the longer term members seem to work well as an accidental team by times.

Thanks. I've got plenty of GA's for cracking jokes, etc. When it comes to the technical stuff, I think the genuine best answers should be at the top of the page. Yours actually hit on something the OP hadn't thought of.

Wow. 30 years in the VFD industry and I have NEVER seen this kind of situation. Not the control / output problem, but the odd arrangement of single phase utility power and a 3 phase backup generator. Very interesting. At first glance I can't see anything wrong with the approach, I'm just shocked to see something I have never even thought of, let alone come across. You get a cookie for Stumping the Chump!

Surging (or more likely, "Hunting") on the other hand, seen that plenty of times. So some background if you please.

PID loop being used in the VFDs? Sounds like a No, that the VFDs are just following the PLC signal. Just making sure.

If it's just a PLC follower in the VFDs, is there a PID loop in the PLC? If so, what's the PV coming from?

One signal from the PLC split into the drives, or in series (if it's 4-20ma), or two completely different analog outputs from the PLC, isolated from each other?

Safe to assume you used shielded wire for the signals and only grounded one end?

With this odd 1 phase / 3 phase / ATS arrangement, how are you handling the neutral on the single phase service?

Safe to assume its a 3 phase delta on the genset output, but is it high leg, corner grounded, or floating?

When you say one starts up fine and runs, then the other one surges, is there a timing function in the PLC Run command that staggers them? Or are both VFDs being re-initialized at the same time, but responding differently?

When you say the pressure is low, what is measuring that? If the device is electronic, any chance it is getting a squirrelly signal that is giving you a false reading? In other words, did you check to make sure what it's telling you is corroborated by a different device?

Can't think of any more right now, but that may change.

Monday morning, back to work...

Manually set VFD speed reference through PLC from HMI, retained across restarts. No PID in VFDs, separate AOs to VFDs. NEVER ground shields at both ends, good way to ensure screwy operation.

I will have to contact customer for questions on feeds, we furnished control panel with VFDs, PLC, and HMI, electrical work done by other (local) contractors.

PLC starts Pump 1, which surges, first, then starts Pump 2, which runs fine, after a five second time delay in PLC. Both drives are fed same reference over separate AO channels.

Hydrostatic head in wells is measured by submerged pressure transmitter, one per well. 4-20mA output back to PLC AI channels. Both transmitters have been verified using direct measurement, both agree with actual measured water heights. We know the depth of level xmtrs in wells, and can measure height of water in well.

I think JRaef may have hit on something. Details on how the generator is grounded please?

How long are the VFD to the pump conductors? If the generator is not grounded, I can see the possibility of capacatince issues causing problems on transition back to the grounded utility source.

I have seen this before. The ABB VFD is the common item. The pumps you have are quite a lot smaller than I worked on. When you shift from utility to power, the time delay is sufficient to allow all the water to drain back out because the generator takes time to start up. When the operator shuts it off, it doesn't turn back on mmediately. No problems right? When the utility comes on, the transfer is fast, and if one of the motors is running backwards due to the draining water, the ABB drive gets confused and tries to continue the same rotation. Pumps are nortoriously inefficient running backwards. If this is like the VFD that I had, it was programable for a delay on restart due to loss of power, if not it can be done on the programable controller. Either way, you need a slight delay after any shut down of the pump, and it should have been programmed in. It is easy to time the pump for run down after removing power to determine the amount of delay needed. Many pumps will coast down and then reverse mechanically due to a water collum and finally come to a rest. Try a shutdown and see if that is happening. If not, I still think a little time delay after shutdown or utility transfer will fix the problem.

That sounds feasible, but why wouldn't the check valves prevent that from happening?

The water shouldn't be flowing backwards.

In a lot of Submersible well pump designs, there is no check valve except at the top, the water is allowed to fall back down the hole to avoid having the weight of it on the pipe all of the time. So when turned off, the pump spins backward for a few seconds, but it can be a lot longer depending on the depth.

Ah. So the delay idea might just do the trick.

Adding a delay after power restore is an excellent idea. Your scenario is highly probable. Wells aren't very deep, 40', but I could see there would be some spin-back.

• Adding a delay after power restore is an excellent idea. Your scenario is highly probable. Wells aren't very deep, 40', but I could see there would be some spin-back.

Yes. It's also especially problematic if you have "Flying Restart" enabled (not sure what ABB calls it). Flying Restart is a way for the drive to monitor an already spinning motor and "catch up" the VFD's output frequency to match it so that you don't connect to the motor out of phase. However if the motor is spinning the OPPOSITE direction from what the VFD is being told to run, the Flying Restart circuit is attempting to stop the motor by reversing it first, then that can cause it to go into current limit, which limits torque and in a submersible with no check valve, can allow the water start falling again, which keeps it spinning backward, which causes it to current limit etc. etc. etc.

A quick check shows that ABB calls it "Flying Start" and it's done in parameter 2101, set to 3 or 5. You should never need Flying Start on a submersible pump, I would disable it if it's enabled. Common error by the way. Flying Start is a great feature for a lot of things, and techs often enable it out of habit when commissioning a drive.

Well, we sent an experienced engineer up to the site today (I couldn't go because of previous commitments), and what the issue looks like is that we must allow the drives to power down completely before we re-energize with a source having different # of phases. No problem on transition from utility (1 phase) to generator (3 phase) as ATS waits until generator output up and stable before switching to generator, which gives drives time to power down.

On the other side, switching from generator to utility is almost instantaneous, so drive doesn't get to power down completely and drive gets confused, thinking it lost a phase somehow.

We will have to add contactors on the drive inputs so that we can hold off re-energizing the drives when the ATS switches.

Huh. I cannot for the life of me think of a reason why a drive would "get confused" based on a change in the number of phases coming into the rectifier.
If that were true, then losing a phase on a 3 phase drive would be exactly the same. I have had phases lost of 3 phase VFDs literally hundreds of times, I have never seen a drive get "confused". Overloaded? Yes. But yours are properly sized, shouldn't make any difference whatsoever.

I would expect it is still just based on the delay that is inherent in the transfer to the generator and that going the other way, there is no delay (or less delay).

Normally, I would agree, but I checked the ACS550 documentation, and it does detect and fault on excess ripple in DC bus voltage which can be caused by loss of supply phase. My understanding is that the drive takes ripple measurements starting at power-up, and if it suddenly increases over the average to date, reports it as a supply phase loss.

Which means if you start with 3 phase and suddenly switch to 1 phase without the drive resetting its ripple voltage average by powering down, it will throw a hissy fit. Switching from 1 phase to 3 phase would decrease ripple, which is just hunky-dory as far as it is concerned.

Sometimes, you can have too many diagnostics.

Quote:

^{Normally, I would agree, but I checked the ACS550 documentation, and it does detect and fault on excess ripple in DC bus voltage which can be caused by loss of supply phase. My understanding is that the drive takes ripple measurements starting at power-up, and if it suddenly increases over the average to date, reports it as a supply phase loss.}

<sup>Which means if you start with 3 phase and suddenly switch to 1 phase without the drive resetting its ripple voltage average by powering down, it will throw a hissy fit. Switching from 1 phase to 3 phase would decrease ripple, which is just hunky-dory as far as it is concerned.

Sometimes, you can have too many diagnostics.</sup>

You know, that actually is a great theory. Like I said, this dual source 1-phase / 3-phase situation is something I've never come across before, and DC bus ripple monitoring is also relatively new. I knew it is used to detect phase loss, but I was thinking that because of the drive being over sized to get enough capacitance, it wouldn't make a difference. And it probably wouldn't if the DC bus ripple monitoring wasn't going on, or the phase loss was not sudden. But the sudden CHANGE and instability of the measuring parameters seems very plausible as the culprit to causing unpredictable reactions.

I also now wonder if you have DC bus regulation turned on, and the change in output frequency was the drive's attempt at doing something about it?

Something new to file away in the vault. Thanks!

I had assumed when you mentioned that the back up generator was 3 phase, that you only used 1 phase from the genset to feed the transfer switches. You mean to tell me that you use all three phases when on the generator?

If so... that is very weired. How is this mess grounded?

I don't know. Electrical installation was by another contractor. We furnished control panel with drives, PLC and HMI. I will find out.