Lenze VFD Automatic Start & Current Fault

[jbuck]

I have an Atlas Copco rotary vane pump which is wired into a temperature on/off switch (Johnson Controls) so the pump and start and stop based on my outside air temperature settings. It is powered with a Lenze VFD. This pump station is remote and it's not practical to visit each time I want to start or stop the pump according to sap flow.

The issue I run into is upon a cold startup, the pump will begin to turn and ramp up to operating speed for a few minutes but then shut off due to an over current fault from the VFD. The VFD does not automatically reset and requires a power cycle to reset and start again (again, not practical). However, the same thing happens after a restart unless I close the inlet valve to the pump so the oil heats up faster. The pump oil is cool so viscosity is high, so it takes more current to run the pump at rated speed. The pump rated power is 3HP and rated current is 9A. I have been slowly increasing the overcurrent trip setting on the VFD to 12-13 amps to try to allow the pump to warm up before it trips, but have not been successful yet. I don't want to allow too much current into the motor for too long.

Has anyone else set up one of these vane pumps this way? I'm curious how other people avoid this problem. Two possible ways to solve the problem might be to enable a VFD automatic reset function if it exists or derive the right short term electrical current limit so the pump motor continues to run and warm up the oil.

Thanks for any advice out there!

James

[DrTimPerkins]

Cold starts can be a problem for pumps, especially with the larger pumps that have a lot of inertia when they first ramp up. Can you put a heat lamp on it so it stays warm? Maybe use a lower viscosity oil early in the season and change it when it gets warmer.

You might be able to program the VFD so it ramps up really slowly at first so the current draw isn't as high.

[wmick]

Couple ideas...
Like Dr Tim said... 1.Have a look at your acceleration time program... Im looking at a Lenze manual and this one is able to be set as high as 3600 seconds (1 hour)
2. Consider synthetic oil... They tend to be far less prone to viscosity change with temperature.... I use it for gear-boxes on equipment in cold areas, for exactly the same problem.
3. Check your programming for an "auto restart function"... the manual I am looking at, has one... Parameter P110.
4. Magnetic Oil Pan heater... Not sure if you have any flat spots you could stick one... I use them on a couple compressors, to keep the oil warm for starting. (I also use them on tractors)https://www.amazon.ca/Zerostart-3400017-Portable-Electric-Transmissions/dp/B0076DUV2Q


If you have a make and model of your VFD, Id be happy to take a further look at the parameters for you.

Good luck

[GeneralStark]

I have zero experience with vane pumps but I have also had issues with over amperage with my liquid ring pump when there were lots of leaks in the woods, typically first run of the season, or when a bunch of drops popped off spouts. I had set up the VFD for the pump using the high current rating on the pump, but the manufacturer of the pump says it is ok to run at a higher amperage so since I bumped up the setting on the VFD I haven't had an issue.

So, one thought is to determine what is the highest amperage you can safely run the pump at for a sustained period of time. Perhaps you can get away with a higher over amperage setting without damaging the motor....

Something else to consider is just running the pump 24/7 and ridding yourself of any concerns related to the pump starting and stopping etc... I'm pretty sure this type of pump can be set up with a vac. transducer so the VFD will turn the pump down when the sap freezes up. Either way, the cost of electricity will likely be offset by more sap and less trouble.

[Amber Gold]

I second what Hogback said. Just run the pump all the time. There's been days when I thought there's no way I'm getting sap today, and stop at the woods for a quick check and found I got a decent run. If you leave the pump running, you know you'll get any sap that's coming to you, and you're eliminating a possible failure point...the temp sensor.

You could put a vac. transducer in, and I have one that's been sitting on the shelf for 5 years...but my philosophy is I want all the vac. I can get...and then it brings in another failure point.

[Shaun]

I also run my 3HP vane pump all season. These industrial pumps like to stay running.

[jbuck]

Thanks all, very good points and suggestions. I'll make some adjustments and let you know how it goes. It may take a few iterations of changing one parameter at a time since other external factors change at the same time (outside temp, leak volumes, etc.). But I think the pump motor acceleration time constant is likely the best way to solve the problem. I understand the position many have about just leaving the pump on 24-7 (manual ON/OFF), but in my case I'd prefer to have more autonomous operation because of the remote woods location. Thanks again.

[DrTimPerkins]

I guess the other thing I'd add is that you should do regular maintenance with these pumps during and off-season, Typically just a very small amount of the specified lubricant added slowly into the vacuum stream while the pump is running. We tend to turn ours only once a month for an hour or so just to exercise them. The tolerances are so tight on these pumps that even a small amount of rust is not a good thing. We also have found that sending them back for cleaning/retuning every 4-5 yrs keeps them running in really good condition.