Variable Frequency Drive Issues

[jweav2223]

I have 3 Duplex Pump Skids installed at a Treatment Facility. Each skid has 2 Eaton DG1 VFD's installed in the controls. This was my first time to use Drives from Eaton and everything tested find in our facility. Once installed at the customers location the Drives started doing something strange. When I came up to troubleshoot I noticed immediately that 4 of 6 Drives were displaying "NRD" instead of "STP" which I was used to seeing. I cycled power and that did nothing. After talking with Eaton Support I checked the current setting for DC Link Voltage via their Monitoring screen and it was showing 0. For some reason I never did check with my Meter. We discussed with it being 0 instead of 670ish like I should be seeing I had some Drive issues. Last resort they mentioned doing a factory reset. Randomly this resolved the issue as soon as I engaged this feature it switched to "STP". Since I changed minimal settings (Accel, Decel, Preset Speed) it was quick. Tested operation and it worked great. However the next day the customer cycled power and this caused the Drive to return to the "NRD" (Not Ready) state and DC Link Voltage displayed the 0 again. They could do the factory reset and it would switch to "STP" and run normal. Yet every time they cycled power it did this. Any one else see this before?

 

[Highland Controls]

I know nothing about the Eaton drives, but drives typically have voltage on the DC bus as soon as the main AC input turns on. Does this drive have a dedicated control voltage input(24VDC) that allowed the display to be powered without the mains? Did you check AC input voltage at the drive? Are there contactors ahead of the drives?

 

[jweav2223]

I know minimal about Eaton Drives as well. We by standard use Altivar Drives from Schneider but Engineer wanted Eaton. I have a separate external power supply going to the Drives. Line Power at the Drives are 482 Phase to Phase and 277 Phase to Ground Lug of Incoming Power. There is no Contactor ahead of the Drives as it goes Distribution Block --> Breaker (MCP) --> VFD Line Terminals. I didn't actually check the DC Bus Voltage but the Monitor was showing 0. When I did the factory reset of the settings it changed to the ~670 as expected to be there and operated fine. Cycle power and again it would change status state from STP to NRD for Not Ready and not allow any operations until the factor reset was completed again. I did notice the DigIn they told me to loop my 24+ to for Run Enable is factory set to EXT FAULT 1 NO. The Drive isn't in a Fault state though at start up with 24+ at this DigIn and the NRD issue was not seen during testing in our shop. I also don't think this would effect the 0 DC Link Bus.

 

[jraef]

That drive has an SCR front end (rectifier) as opposed to a simpler Diode front end. That means there is a firing circuit for the SCRs. They do this to get rid of what's called a "pre-charge" resistor circuit in the drive that prevents damage to the components from the capacitor charging current inrush when you first energize the line terminals. In a pre-charge resistor circuit, there is a current limiting resistor in series, which is shorted out after a few seconds (or they use an NTC resistor). The alternative is to use SCRs instead of diodes, and ramp the voltage into the caps to prevent the inrush. But as I said, SCRs then require a gate firing circuit instead of a resistor shorting circuit, so it tended to only be done on larger drives.

What has changed in the latest generation of drives is that the drives are all made now with "IPM" devices, "Intelligent Power Modules", which are a single potted device that contains all of the transistors and all of the diodes or SCRs, along with all of the firing circuits for them in one monolithic block. So for the VFD mfr, since the firing circuit fro the SRCs is already there, all they need to do is interface with it on the mP comm bus.

What that means here however is that something is interfering with the command signal to the IPM telling the SCRs to fire, which means the DC bus is not getting voltage through the rectifier. What is causing that is the only actual mystery here. Eaton (or Vacon who actually make the drives) might be able to tell, but would need the drives back for forensic analysis.

What YOU need to do first is to see if you can duplicate this when on a different power system, to eliminate a noise or interference issue as the cause. So remove one of the drives and take it to a different building to power it up. If it still does this, the drive is defective. If not, there is something in the local power system causing the SCRs to not fire. My guess would be something on the line that is causing severe line notching. For SCRs to fire correctly, the system must determine the zero-cross reference point of the sine wave coming in. If that sine wave is very noisy, it can be filtered, but if there is severe line notching, the zero crosses of the notches can "fool" the sensor circuit of the gate driver and it shuts down to prevent misfires and catastrophic failure.

If it does work fine elsewhere, look around at any other nearby machinery for something with an old (or really cheap) DC drive. They were notorious for causing that. Some other older linear power supply that is starting to fail might also do that, even and older lighting ballast on its last legs.

 

[jweav2223]

I will try to remove one and see if I can duplicate the issue. We connected to our 480VAC in shop and the issue was never seen during test so makes me believe it will not be duplicated. These are located in a large government facility in their treatment building. Lots of older and newer equipment mixed in together tightly in this building so could be lots of things creating the noise you're suggesting. Would a Filter on the Line Side help?

 

[Gary Lee D]

Not knowing how you have this wired and configured this is a bit of a stab in the dark.
If you have you run or stop bridged out permanently then check the settings of these inputs. Some drives have the option f setting these as simply inputs or having to see a change of state, ie true to false or vice versa, rising or falling, etc etc.
This would explain why a factory reset changed its state.
Good luck

 

[jweav2223]

Nothing special with wiring. One DigIn is programmed to Run Forward at AI2 Speed Reference. A second DigIn is programmed for Preset Speed 1. So if just one DigIn active (1-0)) then VFD Runs Forward looking at AI2 for reference speed. If that one and the other are active (1-1) the VFD Runs Forward at Preset Speed setting. Once they both are not active (0-0) the VFD Stops.

For the person mentioning the noise. I have (2) 2HP, (2) 3HP and (2) 40HP set ups. They are within a 40ft x 25ft section of this facility. The smaller versions are the only ones doing this. The 40HP have never had the NRD issue (0 Bus Voltage). I'm not very knowledgeable on noise so this may be a dumb question. Possible that the "noise" is not so much to effect the 40HP but can effect the smaller units?

 

[mendonsy]

Have you tried starting each one individually with the other drives shut off to isolate the source of the problem??
If the smaller drives run when the 40hp is shut down then you definitely need to install line side reactors (probably a good idea anyway). If they don't run then something else is causing the problem.

 

[jweav2223]

Issue happens when I cycle power to the station. It doesn't matter if the others are running, disconnect engaged or with power to the Drives. It has happened with everything just sitting idle and it has never happened while actually operating the Motors.

 

[DwSoFt]

I would deffinitely talk to eaton tech support on this one. they have helped me a few times with faulty equipment.

 

[jweav2223]

Randomness of the issue we're having. The Drives apparently are very sensitive to the 24VDC that is being supplied to it. I had exactly 24VDC to it when measured with a Meter. The Drives would be NRD. If I dial the voltage up it would stay at the NRD Status and also Fault. Dial the voltage back down to 23.3.-23.7 area and it would switch to STP and allow me to run. Anything roughly 23.2 or less would NRD again. Go back up to around 23.5-23.7 and it would switch to STP again. Eaton Support said they recommended it to be around 23.7 instead of 24 and mentioned it was very sensitive to the supplied power.

 

[g.mccormick]

Randomness of the issue we're having. The Drives apparently are very sensitive to the 24VDC that is being supplied to it. I had exactly 24VDC to it when measured with a Meter. The Drives would be NRD. If I dial the voltage up it would stay at the NRD Status and also Fault. Dial the voltage back down to 23.3.-23.7 area and it would switch to STP and allow me to run. Anything roughly 23.2 or less would NRD again. Go back up to around 23.5-23.7 and it would switch to STP again. Eaton Support said they recommended it to be around 23.7 instead of 24 and mentioned it was very sensitive to the supplied power.

holy craps that was the issue? .3 volts between all good and all ****. If using the internal 24 source, is the issue mitigated?

 

[jweav2223]

Seems to have been the issue. We have 3 duplex pump skids at this site for a total of 6 Drives. Each skid has a 24VDC Power Supply. I adjust all 3 Power Supplies in that range and they would change from NRD to STP. Did the up above the range and NRD and eventually Fault every time. Go below the range every time back to NRD. Very tight window to be in and quite strange for that window to actually below 24VDC as a lot of units are regulated at this voltage. We are not using the internal power supply and didn't check to see what would happen if using it.

 

[jraef]

Wow... that's a tight operating range for an industrial product.