"Current" Woes

Hello
I have multiple extruders that use 4-37KW 980 RPM 74 Amps 380Volt motors. This is attached to an appropriate Abb ACS 600 series Drive. The motor leads for this machine are all attached to the output of the drive then breakout to each motor through an overload set for 75 amps.
All parameters for the drives on multiple identical Extruders are the same except the extruder with the problem has parameter #31.04 which is under automatic resets section; it turns on or off automatic reset for OVERCURRENT alarms. This is turn off on the problem drive and the other running extruder has it turned on.
We completed a rebuild to the extruder gear box on June 2, 2009 and ran the extruder Starting June 8, 2009 we started to get OVERCURRENT faults on the drive. We could not find anything obvious our feeling is that the gearbox is running correctly. When trending the output of the drive we did not see the extruder running near current limit We amp probed all 4 motors and found one motor of the four was drawing about 10 more amps than the other 3 motors. We have another motor from a spare machine and on June 16, 2009 we replaced the motor. The extruder seem to run fine. All 4 motor loads seem within 1 to 2 amps.
Starting yesterday July 20, 2009 we started getting OVERCURRENT faults from the Extruder again. We see one motor drawing about 6 amps or so more than the other 3 motors. It is not the replacement motor that has the greater load.
The spare machine does have 2 more motors so I can change the motor.
But I have to wonder
How 2 motors from the same machine can go “a little bad”
Should I just expect to need to change all the remaining motors?
What do I tell the motor repair shop to look for while trying to fix the removed motors?
Could it be as simple as changing the 31.04 parameter and hopefully the drive will ride through the issue?
Can the current sensing “loop” of the drive go “soft”?
Can the current sensing “loop” of the drive be tested?

I am currently working on borrowed time. I am also getting some conflicting advice from my “circle of experts” and would greatly appreciate any thoughts, comments or idea’s you may have.
Thanks for the help
Michael

A couple of possibilities,

First, have you checked the voltage at the problem extruder? It may be at the end of a heavuly loaded distribution network, and voltage drop would cause the motor to pull more current for the same hp.

Second, are you sure that there isn't an actual mechanical issue with the problem extruder that causes it to occasionally pull higher current, damaging the motor?

Is there proper air flow around the motors? Excess heat can cause the coils to melt and arc.

Maybe a case fan has gone bad if they are in an enclosure. Maybe the area is not getting cooled by the HVAC well enough.

We have seen strange problems with identical machine occur because of a few degrees difference in air temperature around them.

Or maybe you have more dirt in that area that has gotten into the motors?

Maybe the other motors were damaged when the first motor went out. Now they are pre-disposed to failing and it is only a question of when?

Maybe..... guess I am all out for now.

I agree with Tom, I would first be looking for any connection point (including the overload connections themselves) where there could be a voltage drop. These type of poor connections will only get worse as they heat/cool with useage.

mrdegold said:

Hello
Abb ACS 600 series Drive.

Click to expand...

These are tough old brutes!

mrdegold said:

All parameters for the drives on multiple identical Extruders are the same except the extruder with the problem has parameter #31.04 which is under automatic resets section; it turns on or off automatic reset for OVERCURRENT alarms. This is turn off on the problem drive and the other running extruder has it turned on.

Click to expand...

Michael,

Perhaps the "Good" machine resets itself and you never know!

mrdegold said:

Can the current sensing “loop” of the drive go “soft”?

Click to expand...

I have had a current sensing device from a ancient Square D drive go bad. This must have happened before I was involved with this company as they had two in the stock room and no other spare parts for this drive.

I would PM Dick DV he's very sharp on on ABB drives.

mrdegold said:

Hello
I have multiple extruders that use 4-37KW 980 RPM 74 Amps 380Volt motors. This is attached to an appropriate Abb ACS 600 series Drive. The motor leads for this machine are all attached to the output of the drive then breakout to each motor through an overload set for 75 amps.
All parameters for the drives on multiple identical Extruders are the same except the extruder with the problem has parameter #31.04 which is under automatic resets section; it turns on or off automatic reset for OVERCURRENT alarms. This is turn off on the problem drive and the other running extruder has it turned on.
We completed a rebuild to the extruder gear box on June 2, 2009 and ran the extruder Starting June 8, 2009 we started to get OVERCURRENT faults on the drive. We could not find anything obvious our feeling is that the gearbox is running correctly. When trending the output of the drive we did not see the extruder running near current limit We amp probed all 4 motors and found one motor of the four was drawing about 10 more amps than the other 3 motors. We have another motor from a spare machine and on June 16, 2009 we replaced the motor. The extruder seem to run fine. All 4 motor loads seem within 1 to 2 amps.
Starting yesterday July 20, 2009 we started getting OVERCURRENT faults from the Extruder again. We see one motor drawing about 6 amps or so more than the other 3 motors. It is not the replacement motor that has the greater load.
The spare machine does have 2 more motors so I can change the motor.
But I have to wonder
How 2 motors from the same machine can go “a little bad”
Should I just expect to need to change all the remaining motors?
What do I tell the motor repair shop to look for while trying to fix the removed motors?
Could it be as simple as changing the 31.04 parameter and hopefully the drive will ride through the issue?
Can the current sensing “loop” of the drive go “soft”?
Can the current sensing “loop” of the drive be tested?

I am currently working on borrowed time. I am also getting some conflicting advice from my “circle of experts” and would greatly appreciate any thoughts, comments or idea’s you may have. hanks for the help Michael

Click to expand...

OK lessee if I have this right.

You are using a single VFD to drive the motors on 4 extruders.
Each extruder is mechanically independent from any other.
The only thing in common to all 4 is VFD.
Each 380V 37 Kw 74 amp motor has overload set for 75 amp.

#1 extruder - rebuilt gearbox June 2, 2009 gearbox seem OK
Starting June 8, 2009 started getting overload faults on drive. Motor drawing normal amperes according to trending

???? extruder Jun 8 motor drawing 10 amps more than others. Replaced motor with spare June 16. All seems OK.
WHICH EXTRUDER??

Jun 20 VFD overload trips again.

How is VFD put together ie one IGBT and set of CTs
OR one set of controls and 4 IGBT and 4 CTs?

Where did you get trending data? Is this for all four motors?

Are these screw type extruders?
Have you pulled the screws?
How old are they?

Are all four extruders fed with the same material?
IS IT really the same?
Are the all extruding the same product?

Recommend putting ammeters on all four motors and keep a close eye on them.

Dan Bentler

Sorry for the confusion
I am driving 4 motor on the same Twin screw extruder. Each motor mechanical connected to the other 3.
My plant currently has 5 of this same model extruder.
I am attaching an image that may clear this up some.
I think what we'll do first is change the parameter and try to run I agree with milldrone that perhaps all the other extruders see this issues but ride past it because of this setting. Beside what do I got to loose?
I am one who would always prefer to have a couple steps plan out in advance. What do I do if this parameter change doesn’t work? I can always change the motor. But I am still troubled by what to I tell my motor repair shop to fix??
Thanks for the help
Michael

Since they're all mechanically coupled, any physical differences between the motors will likely result in one or more of them handling more of the load, and therefore drawing more amps.

I would suggest that you perform a test with a megger on all of the motors and the wiring to ensure that one of them does not have a problem which is affecting the drive.

Be sure to disconnect the leads from the VFD if you do this.

Paul

OK that changes things
We now have extruder 1
Driven by motors A B C D.
Changed motor A replace with A.1
Next another motor starts runnin high
Was that A.1 or ??

One of the rules I have found valuable is
go back to the last thing you did
SO
I would go back to the gearbox. Especially so if it is becoming the same position motor having problems. Are these C face motors that bolt onto geabox individually with all four in a planetary arrangement driving one gear OR ?? Is motor driven gear (hi speed) mounted on motor shaft or in gearbox? What kind of shape are motor bearings in?

I am not sure you have motor problems so would not jump and ship motor off to shop unless you want it checked out - especially if they can load it on a dyno - might be worth a couple hundred to get a clean bill of health.

How dirty are the motors. Extruders I had to work on looked like garbage dumps. Check cooling fans and filters.

is each motor on its own IGBT or are the motors paralleled off one IGBT?
Check connections of course and use IR to check for heating.

Dan Bentler

mrdegold, I have rather deep roots with the ACS600 and can probably help you at least from the drive end. First, the setting of 31.04 matters nothing if 31.01 is zero. If 31.01 is more than zero, it is true that the drive will attempt a reset of an overcurrent fault if 31.04 is on but it would only do that after the delays programmed into 31.02 and 31.03. If an extruder stopped and restarted like that, I believe you would hear about it because a lot of product would be scrap. Actually, I sincerely hope that 31.01 is programmed to zero. An automatic restart on an industrial machine is horrendously dangerous and, whoever programmed it that way deserves a lot more than a severe scolding.

Second, check the setting of 20.03 Maximum Current. When the motors in total try to draw more current than this level, the drive will slow the motors down to try to avoid the excess current. If the operators are not reporting these kinds of speed disturbances, it is unlikely that the problem is mechanical binding or product viscosity, etc. I'm assuming that 20.03 is set somewhere close to the total FLA of 300amps.

Third, if, as you report, the drive is actually faulting on Overcurrent then the drive is seeing rapidly rising current far above the Maximum Current level. Actually, the drive is trying to protect itself when it faults this way. By far, the most likely cause is flashing from phase to phase either in the motors or in the motor leads. Meggering may not reveal the defect since it seems to "heal" as the motor cools and restarts.

Strange as it may seem, I believe that the motors are probably at fault here. Before you sent one off to a motor shop, check to see that drive parameter 30.17 Earth Fault is set to Fault. If it is (and it should be) then you can also tell the motor shop that it is most likely a phase to phase defect, not phase to ground. The ACS600 is very good at detecting ground faults but, if 30.17 is turned off, then it will allow the ground fault current to rise high enough to cause a drive Overcurrent or even a Short Circuit fault.

I'd surely be interested in what you find. Let us know.

""Third, if, as you report, the drive is actually faulting on Overcurrent then the drive is seeing rapidly rising current far above the Maximum Current level. Actually, the drive is trying to protect itself when it faults this way. By far, the most likely cause is flashing from phase to phase either in the motors or in the motor leads. Meggering may not reveal the defect since it seems to "heal" as the motor cools and restarts."""

DICK Let me check this flashing would be more common in older motors than in MG 1 pt 31 BUT how common in the MG 1 pt 31 is it to the point of being a problem and then require rewind?
Thanks for mentioning that "healing phenonym" explains why a VFD would fault out on ground fault and when checked to ground after deenergize and cap bleed off would indicte all /OK phase to phase and any phase to ground (done with Fluke VOM only). Left in shop to dry out for several days tehn ran trouble free for a year that I know of. Have always wondered about that. Real old hobart food mixer.


""Strange as it may seem, I believe that the motors are probably at fault here. Before you sent one off to a motor shop, check to see that drive parameter 30.17 Earth Fault is set to Fault. If it is (and it should be) then you can also tell the motor shop that it is most likely a phase to phase defect, not phase to ground. The ACS600 is very good at detecting ground faults but, if 30.17 is turned off, then it will allow the ground fault current to rise high enough to cause a drive Overcurrent or even a Short Circuit fault"".
DICK Thanks will always ensure ground fault enabled.

Dan Bentler

Going back to the first thing that was done. Was there a failure in the gearbox that caused the rebuild? If so, was the cause of the failure found? At what point are you seeing the overcurrent fault? Is it on startup or after it has been running and up to operating temperature? If you have a good motor shop they can usually tell you what the cause of the failure is. I worked on plastic extruders for 10 years and one thing I have found is that when the screw is worn the shearing between the screw and barrel can cause the extra load and large amounts of heat that can be transfered into the gearbox. Does this gearbox run hotter then the rest? I would find someone with a good Fluke power monitor and take a detailed look at the VFD output waves.

Kevin

First I like to thank everyone for there help I appreciate it.

I will try to answer the additional questions that have been asked as best as possible.
The motor we are seeing the 6 amp gain is mounted to a different physical location than the motor from 5 weeks ago.
Each motor mounts to a gear reducer (transmission) that is then attached to the gearbox.
All motor are powered from a single drive output they share 1 IGBT per phase.
Parameter 31.01 which is the number of automated reset trials has a value.
The trial time (31.02) is set to 30.0 sec.
The Delay time (31.03) is set to 2.0sec
Maximum Current (20.03) is set to 200.0%Ihd
Earth Fault (30.17) is set to fault

What the reason for the original gearbox rebuild was damage to the gears. This machine/gearbox was probably from the mid 1980’s and never done before so my feeling would be more of just wore out.

We have been running these same model extruders for a very long time this machine that is giving me trouble now was run on an Abb sami star drive. Years ago we update the cabinet and replaced that with the ACS 600 series drive. I currently have 2 of these machine using the ACS 600 and 3 more running on ACS 500 series drives all these drives have the automatic reset feature active for overcurrent faults.

My understanding of the function of the automatic reset feature is that it will attempt to reset the fault the number of times set in 31.01 within the time period set in 31.02 waiting the delay time set in 31.03 in-between attempts to reset. I am under the impression that the first attempt is not delayed.

While thinking about this problem I thought that we have be running these machines forever here. I have been trouble shooting them a long time and before me it was the guy I have as our plant Electrician, now it’s the both of us. And neither of us has ever seen any of these 5 machines in all these years do anything like this. We have seen burnt motor’s, oil in pecker heads (and why is it called a pecker head) and yes earth ground faults from the drive. Making me guess I’m missing something stupid.

Thanks again for the help
Michael

Going off on an unlikely, but possible tangent, seeing as everyone else has given the sensible answers.

Check that the earths and screens concerning these motors are tight and in good condition.
My thought being, that cables act as a capacitor, and at higher frequencies, that drives produce, this can build up to a significant value which the drive current needs to also feed.

I did tell you it was a tangent didn't I.

Dan, insulation failure or the beginnings of failure can occur in any motor whether rated MG1P31 or not. The flashing is the prelude to total failure and the ACS600 is very good at detecting the early signs of this.


mrdegold, the way you have 31.02 and 31.03 programmed, the drive will fault and then wait 2 seconds to attempt to reset. If the reset fails, it will wait another 30 seconds and then try again up to however many attempts you have programmed into 31.01. I would think that a two second stop would cause enough upset on an extruder to generate some concern among the operators.

As to programming an industrial machine for automatic reset, I've already made my view of that known. Let it suffice to say that, if I was commissioning the machine and was being forced to program an automatic reset, I would walk off the job before I would do it. I want to end my career without anybody's blood on my hands.

Finally, why a motor junction box is called a "pecker head", I'll leave for someone else to answer. All I know is that it isn't called that everywhere, especially where women are working in the maintenance trades!

I am convinced that you have a motor failing and I see no reason to believe that it necessarily is the one with high amps. With four motors in parallel on a single drive, it becomes almost impossible to sort out the bad actor until the smoke starts to roll. Fortunately, you've got some spares around. What a luxury that is, these days!