mutabi

Ok guys, I touched on this in another thread, and I would really like to get some goo recommendations on what to do.

We have a 30HP motor, turning a belt driven gearbox, connected to some drivelines which turns some arbors, which then cut into a copper tube.

We have 42 of these machines. Every so often we get a machine where the motor will either fault out on overcurrent, or will give a motor stall fault.

We use ABB 600's and 800s to run the motors.

We have been having a lot of trouble with one machine the last month or so. We have changed the motor out with a rebuilt one. We changed the drive out tonight and went from an 800 back to a 600. And still it stalls out. At idle , it pulls about 12 amps. FLA is around 38. If I run the motor at full speed, while cutting the tube, it will pull right at around 38 amps, and get up to 47 amps after a lil while, and then start bogging down before it stalls. Why it doesnt trip out on overcurrent I do not know.

The question is, how can you check to see if the motor is good or bad? CHeck it with a meter phase to phase and its balanced and around 0.2 Ohms. Meg it to ground, and get very high meg Ohms. But that still does not guarantee that the motor is good. Is there any other check?

Yes it could be a load problem, but we can turn the gearbox by hand. It has oil in it. We can turn the arbors by hand no problem. And the guys that set up the arbors to cut the tube, swear up and down that the alignment is good and there is no reason the motor shouldnt run.

Someone must have a solution to this problem. Yes we could step up to a bigger motor, but that would involve convincing the boss, and having to modify machines.

Is it possible that the drive is limiting the torque that the motor has? ANd i dont mean through the various settings. If I run the motor at 30Hz, which is where they like to run it, is the motor running with less torque/hp that if we used a regular motor starter?
How about if we run the motor at 60Hz with the drive(which we have tried)? is it running at full potential then?

Someone please help!

wirenut1110

It sounds to me like your drive is kicking out because of motor slippage at low speeds.

I've been out of this for a while but, the way I understand it, is with a regular voltage/hz drive, you lose torque at low speeds or that the speed/torque/slippage is linear. Like a motor running at 20 hz, it's HP is reduced like 50%. So it would be like your 30 HP offering only 15.

The use of vector drives for particular applications because they can offer 100% torque at zero speed.

PS. Google vector drives and it can explain it a lot better than I can. But it sounds like this is your issue, that your motor is trying to do the same work at 30% speed so your actual HP at that speed is like 18.

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Jim

micromind

Since the motor is belt drive, I'd change the sheaves so as to operate the motor at a higher RPM.

Generally speaking, the torque of a motor will remain about the same at varying RPMs, thus HP follows speed. Higher RPM = higher HP.

HP is what does the actual work, torque is nothing more than stress on a shaft.

Rob

John Valdes

If this were my problem it quickly would become ABB's and your motor shops problem too. These people are paid to market and support their equipment. I know because I used to work in this industry. ABB has one of the best controls on the market.
Have you taken advantage of ABB's training. Does your motor and drive shop have seminars? You need to learn about drives and motors. Call them today. You might be able to correct your issue with a 5 minute phone call. Why bust your butt when they have the answers you need.

Wirenut, You are right on with your post. Slow speeds and low torque are the hallmark of the non-vector type controls. However, he uses the word "stalling". This could mean a number of things.

76nemo

You have a thermal imager at work?

wildleg

the answer to your question is in your question. you have 42 of these and one is bad ? the answer has nothing to do with changing the motor or the sheeve sizes or any other reconfiguration. the answer is finding out what is wrong with this one machine. feel all the bearings, sheeves, belt tensions, gear boxes, check the wire connections, whatever is hot or loose is what is wrong.

__________________
That tiger ain't go crazy; that tiger went tiger! You know when he was really crazy? When he was riding around on a unicycle with a Hitler helmet on! - chris rock

John Valdes

Another thing you might want to check: Are all these machines identical? If so make sure VFD program settings are exactly like the others. You should be able to take all the settings from one VFD and upload these settings to another VFD doing the exact same job. This will at least eliminate a programing error, should there be one. Operators sometimes can make changes without even knowing they did anything.
Have you called ABB and your motor shop yet. I would have done this yesterday. Even if you fix your issue, you should not let the opportunity to learn something from these people to evaporate. You may find yourself in this situation again. Maybe next time you will understand to how to correct it yourself.

g.hope

Hi people, new to the site and this one interest me. There's many ways to attack this problem. As john said, check to see if all 42 machines are really the same, also is the machine doing the same as the others, ie: cutting the same size tube, same rate (eg: 100 pieces per minute),etc. If they are the same, then check the control of the VFD, what I mean, is it PLC control? is it hard-wired (maintaining contactor-relay)? Profibus? Check to see if the VFD is staying enabled, it might be kicking in and out. Check what John said and compare all the parameters in the VFD, also check the motor nameplate with another motor to see if they are the same. You've already changed the motor and that tells me it can't be that. You've changed the VFD, so that should not be it either. If you can, disconnect the gearbox from the tube line, and then run the motor and see what happens, if it runs o.k. then its down the line, if not, check your connections,all the way from your motor to the disconnect to the splitter, you might have something lose or a faulty relay/contactor. If you think it's the VFD, change with one thats working in production now, and see what happens. Good luck!

mutabi

Yes, all 42 machines have the same setup. I.e. VFD-->motor-->belt driven gearbox-->arbors that cut into the tube.

The motors vary between 25HP and 30HP. The one giving trouble was a 30HP. In the end I ended up changing out the motor. But I hate "throwing parts at the problem". I want to be able to justify changing it.

After changing it, the machine ran better, but still occasionally bogs down while cutting (finning) a tube. So there is some problem somewhere.
The drive was changed out as well, and I did make sure its settings matched the motor nameplate.

I can let the machine run continuously without a load i.e. no tube being finned, and it will run just fine. It only bogs down under load.

Its not possible to set the machine up identical to another one, as even though they are all finning tubes, there are different products, different size tubes, and even different tube material.

I would love some way to test to see if the motor is as good as it was when it was new. A megger/meter MAY only tell you if you have a motor problem.

Here is a question, does anyone have access to a frequency/torque graph for running a motor? Like, one that shows at what speed it has full torque, half torque etc

John Valdes

Swap motors. Take the one in question and replace it with one that does not give you any problems. If the problem follows the motor, it's the motor. Same with the drive. I think you have a mechanical issue. What did ABB and the motor shop say? You asked for advice.

p_logix

I hate "shotgun troubleshooters" as well. But this should be pretty simple to troubleshoot you have 42 machines that are alike.

That should have been part of you're predictive maintenance routine.
Megger the motor when it is brand new then continue megging during your PMs and record for trending purposes.

What else would you want it to tell you? You have a bad bearing?


Remember 42 machines were set up the same. I am sure at one point this machine ran fine. I doubt it needs to be re-engineered. Just make sure you have uploaded the parameters from another VFD thats working and download them to the one you are having trouble with. I believe this was already mentioned.

And you believe "the guys".



How many hertz are you running at when the motor faults? I had a problem where a motor ran fine at 17 hertz but when it ramped up to 60 HZ the drive faulted out. The motor megged out as a short to ground. The motor winding insulation was starting to break down and at 17 hertz which was 127 volts, not enough to "jump" or cause a overload, or the VFD to Fault. The megger 500 scale test found the faulty motor.



What exactly is the reading. Do you have at least 1000ohms per volt. VFD's don't like low megs and sometimes it will fault out but run across the line just fine.

Sometimes we run are drives at 90 HZ. This is done when we don't have the proper gearbox in stock and the conv. belt is running to slow.
The higher frequency you run these motors yes the less current draw but your motor windings better have good insulation.

Based on everything you are saying and if all parameters are the same, motor megs out and is balanced, VFD runs fine when you disconnect the T leads from the drive and the VFD is not drawing high current when at speed with no motor/load. All hardwiring and components check out O.K. It is probably a mechanical problem/Jam etc..

This setup doesn't have a brake does it?

__________________
p_logix
"Meggers Don't Lie, Electricians Lie". Go LAKERS!!!!

mutabi

Heck we barely have a PM program let alone a predictive maintenance program. And I am convinced that the people running the PM program, dont think that the electrical side of the PM needs attention.

I would love to be able to spend time megging motors and graphing the results. But we can barely keep up with breakdowns let alone anything else. This recession has meant our numbers have been reduced drastically.

I believe you answered my question there. No way to tell unless we start megging periodically.


Yes we usually upload settings from another VFD.
lol you have a point, and it is something we do come across. However, its very hard to prove someone else has messed up when you dont know how to do their job. Setting up the machines is not easy, can take hours of looking under a microscope.


The motors are rated for around 1170 rpm. We run them routinely from about 300rpm to 800rpm, depending on what product they are running.

Quote:

This setup doesn't have a brake does it?

No brake involved. We even just coast the motor to a stop. Now if it is finning a tube and the drive motor is shut off without opening the arbors, it will come to a complete stop in less than a second. This is done regularly. I dont think it would affect anything though.

Thanks for your help. I would still love to see some RPM Vs Torque chart.

John Valdes

[quote=mutabi;96591]
The motors are rated for around 1170 rpm. We run them routinely from about 300rpm to 800rpm, depending on what product they are running.
[quote]

Two things: Gear Box and RPM.

Whats the ratio of the gearbox? Is it the output from the gearbox that is running at 300-800 RPM or the motor itself?

Fortunately you have a 6 pole motor (1200 RPM) and the gear box.
But, low motor RPM's translate to low torque. Low torque can cause stalling. So tell us whats up with the RPM's. Gear box output or motor speed. This very well could be corrected in short order. Their are several ideas I have now. Tell us more and I will share these ideas with you.

One more thing. Have you changed out the gear box yet? It very well could be the problem.

mutabi

I will have to check into the gearbox ratio, but I believe it is 1:1. The main function of the gearbox is to create 4 shafts out of one as each machine has to have four spinning arbors.

The motors themselves are running between 300 and 800rpm according to the HIM. It does seem like the slower they run, the more they tend to stall. So at lower speed, am I getting lower torque?

John Valdes

If it's 1:1 ratio you have no reduction at all. Your motor cannot be expected to perform at 300 RPM. The torque has fallen down so low it cannot turn anything. This what I suspected as soon as you told us the RPMs.

http://www.abb.com/product/seitp322/...a005dcb0b.aspx

The link above is for the ACS800 series control. This is a torque control/drive. Do you have this drive in torque mode? The drive is designed to give you almost full torque at low RPM's without the need for a feedback device.. You need to contact ABB on this and make sure you have this drive set up properly!

Where do you live? I can get you a contact and phone number. But this is what you should have done to start with.

mutabi

Alright now this is more like it. We did start to upgrade our 600's to 800's, but ya know, I dont believe we knew there was such a thing as torque control on them. In this particular case, we actually downgraded from an 800 to a 600 as we didnt have any spare 800's left, and had just gotten a rebuilt 600 back in.

I will grab a manual on Monday and try to see if I can figure out how to run it in torque control mode.

That was indeed my suspicion, the lower the RPM the lower the torque. I always imagined it like a bicycle going down a hill and trying to get up the next hill. The slower he went the harder it would be to get up the next hill. The faster he went, the more momentum he would have to get up the next hill.

I will update as soon as I find out something. thanks a bunch

mutabi

Dang, welll I did a bit of research online. Yes we do run the drives in DTC mode. There may be some other settings not quite right though. You are right though. ABB needs to be contacted.

John Valdes

Thats right. You could have already had this fixed. One warning. Calling ABB directly is not your best bet. Call the supplier that sold/sells you the drives. They can get the attention of ABB better than you can. Also, they can come to your plant. ABB is going to send you to a master distributor anyway. So just skip that step and call them yourself.

Please let us know what transpires. I would like to know what you find out.

acdrive

I think this is a good advise. Also you can turn to the manufacturer for help.

__________________
ac drives, servo motors, soft starters, frequency inverter

John Valdes

He has one of the best torque controls to be found in ABB. These drives perform extremely well with out the need for encoders or resolvers. I think he has this figured out, as he has not been back since we discussed speed in relationship to torque.

At 300 RPM, I am very confident the drive can produce all the torque required for his application. He does not have an every day run of the mill drive. It's an ABB.

PS.....OP.....Just in case you have not figured this out, have you auto tuned the control? This is a very important step in setting up the ABB drive. It needs to know what you want it to to do. Auto tuning on this drive is performed with a load and in the application. It learns how to operate properly on its own. Auto tune today.