two identical machine VSD faults minutes apart 4

[2571]

Good morning,
Upon starting the plant Monday morning we had major issues with our compressors, Both went down on a VSD error over current. Putting in a bad spot at the moment, I reset one of the machine and cleared the error displayed and attempted to restart. It errored again, on my third attempt the machine stayed running and hasn't stopped. However, the same twin machine next to it did not fair very well. After the plant pressure was up to par, I put the second machine on line (stand by) as I always do, to be ready to help when required the air pressure dipped and it was asked to come on line. It ran for about 30 seconds and had the same error as the first. When I cleared the error and attempted to restart I was witness to a large flash from the bottom of the motor. After megging the motor I learned the windings were shorted together and now have the 200hp motor out to the repair shop to be rewound. I consulted the manufacture of these compressors asking what the heck happened, and the only thing they can contribute the problem to is, this past Sunday was by far the most hot and humid day we have had in a few years. Not to forget we were having several storms and rain this same morning. They fear the motors condensated inside and when I attempted to start it found the weak spots in the winding insulation. I'm not comfortable with this at all and it does give me a sound reason why this had happened.
Both these machine are VSD driven 200 hp Sullair compressors with WEG motors. After all the dust settle and we calmed down we went looking for water but found nothing. Has anyone of you folks seen something like this? Manufacture claims it happens down south a lot. We are near a oil change and test the oil monthly for breakdown. Sample from last month prove the oil is fine but haven’t seen the results to the sample pulled a week ago. My thought is I have a mechanical issue some where.

 

[davidbeach]

Why don't you believe condensation in the motor windings? Do you know that the motor space heaters (do you even have heaters?) were working correctly and that the motors stayed above condensing temperature throughout the whole weekend? You never even said what the VFD error was.

 

[2571]

There is no space heaters, the error read as follows: VSD drive error over current 1. Cutler Hammer Drive

 

[davidbeach]

So, how did you rule out condensation in the windings?

 

[Zogzog]

[q] They fear the motors condensated inside and when I attempted to start it found the weak spots in the winding insulation. I'm not comfortable with this at all and it does give me a sound reason why this had happened [/q]

I am betting "they" are right. Have you tested the motor to determine if insulation failure has occured?

 

[jraef]

As I posted in the other forum where you asked this, I still think it's a condensation issue.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[edison123]

If this was a totally enclosed motor, I don't see how you could have condensation in the inside air, especially when the motor has been running for so long. How old was the winding and is it VFD rated ?

 

[waross]

It doesn't take much moisture to compromise the windings. The heat of the running motor will quickly return any condensation to the vapor phase. NOT finding moisture in a motor does NOT mean that it hasn't been damaged by condensation.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

So these motors were shut down on a Friday afternoon and restarted on a Monday morning? Two and a half days and three nights? Where any of the nights cool?

And you are near the Great Lakes?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

If this was a totally enclosed motor, I don't see how you could have condensation in the inside air, especially when the motor has been running for so long. How old was the winding and is it VFD rated ?

D we know it was TENV? Even so, a small amount of air exchange through conduits is all it takes. TENV does not mean wash down and vapor tight (or vapour tight for some of you). I used to work for a company based in Florida, this was a constant problem.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[jraef]

So these motors were shut down on a Friday afternoon and restarted on a Monday morning? Two and a half days and three nights? Where any of the nights cool?

Keith,
I don't think you and I (being West Coast guys) have an appreciation for how this works in the Southeast. The Dew Point at 90% humidity can be 90 degrees F!

Cool is relative...


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[LionelHutz]

It's not likely to be a mechanical issue or anything related to a gearbox or the compressor part.

A VFD will find any weak spot in the motor insulation, be it a poor winding job or weakened due to moisture or anything else for that matter.

If you are in a damp humid enviroment then a strip heater that is powered when the motor is stopped is a good idea.

What did the re-wind shop find inside the motor? Did you ask them to take a good look at the failure?

I have seen a number of motors where the factory winding job was poor and that was the weak spot where they failed. Actually, I think every time we've been dragged into a VFD related motor failure problem and we look in the motor we find the same thing. Typically, there is a spot on the end windings where the wire from different phases cross and touch each other imposing all or most of the phase to phase voltage directly on the varnish. Despite the claims that the varnish is good for 3kV or 4kV or whatever they're up to this week, it still fails. Add some moisture or humidity to that spot and it's even more prone to fail.

 

[2571]

Thank you everyone for your replies. to answer some of the questions. I can't rule out condensation, maybe because I have never seen it until now is why I can't wrap my head around it. The motor isn't enclosed it has four large air vent that allows you to see straight into the windings. This being the third year since I had installed these compressors and several other compressors had been in the same room just didn't seem likely. I don't mean to come off as rejecting the idea just really scrambling to find the answers for my own piece of mind and upper management. We are getting our motor back today and I have to be honest I'm very nervous about the whole thing. We haven't even shut the other machine off in fear it may not start. I'm really trying to learn from this experience but damn this is nerve racking. No pressure here!!!!
Davidbeach had asked if it was cool in the morning to answer that yes it was, we hit 91 on Sunday and very humid, then Monday morning we were in heavy storms and pouring rain about 65 degrees. I'm only 30 mile from the Saginaw Bay.

 

[sreid]

Although it's probably "Belts and Straps," since you are having the motor rewound you could have 1) the stator wound using magnet wire with Quad Build varnish 2) have the stator vacuum impregnated and 3) have the stator "Tropicallized."

 

[Zogzog]

I am headed to Saginaw bay tommorow. Did you ever test the motor before having it rewound? What were the test results? You only mentioned you meggered the motor and the windings were "shorted together", that is what you should see meggering phase to phsae. Did you check the winding insulation to ground? I hate to say it but you may have jumped the gun rewinding this motor.

 

[davidbeach]

Condensation, and you just hit the jackpot Monday in that both went at the same time. Probably many cycles of condensation and drying and this was just the time for the insulation to pinhole. Add heaters to keep the motors above the dew point when they are shut off.

 

[edison123]

Ah, an open type motor. That could have a condensation issue, I suppose. Did the rewind shop fit some heaters at least now and rewind the stator for VFD duty ? A failure report from that rewind shop would help in identifying the cause.

 

[waross]

Here is a suggested strip heater that should give protection.
Apply 120 Volts to a 240 Volt rated heater.
Web page;

http://www.chromalox.com/productcat...trip++Ring++Disc/OT/model-details.aspx?m=3528

Part number;
129365 OT-817 IRON 240V1P 175W
Or
Web page;

http://www.chromalox.com/productcat...lexible+Heaters/SLN/model-details.aspx?m=3595

Part numer;
121523 SL-N-1-10-0-10-S-120V-50W
If you have room inside the end bell, lay one of these inside the end bell at each end of the motor.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[2571]

zogzog,
Feel free to stop by,I could tell you where the fish are if that the nature of your visit, any suggestion for this weekend until I receive these heater? Wrap the motors with shipping blankets, turn the wall heaters on and keep the whole room warm? I starting to buy into the condensation theory it seems to be the only thing that the two have in common. you had asked if the motor was tested prior to rewind yes we have a dual wye wound motor and it was between the two wyes was what was shorted. We had also surge test the motor. It was tough to see on the scope but you could hear it plain as day. Sounded like a card in bicycle spokes. Please be patient with me, this was a new experience for me. I have no one else to turn too. Thanks again everyone.

 

[waross]

The condensation occurs when the dew point of the ambient air is above the interior temperature of the motor core. The best use of heaters is to apply a small amount of heat to the machine frame where it will heat the core by conduction. It doesn't take much heat.
In the mean time, a controlled steady temperature in the room is the best.
Rising temperature combined with a rising dew point are the conditions to be avoided. The motor core temperature does not rise fast enough and when the dew point goes above the core temperature condensation results.
Normally raising the temperature of a mass of air drops the relative humidity. But should a mass of warm moist air drift in from a nearby body of water or swamp, the stage is set for internal condensation.
Until you get some heaters, a steady temperature and no air changes is the best way to avoid condensation.

Bill
--------------------
"Why not the best?"
Jimmy Carter