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two identical machine VSD faults minutes apart
4

two identical machine VSD faults minutes apart

two identical machine VSD faults minutes apart

(OP)
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.

RE: two identical machine VSD faults minutes apart

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.

RE: two identical machine VSD faults minutes apart

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

RE: two identical machine VSD faults minutes apart

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

RE: two identical machine VSD faults minutes apart

[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?

RE: two identical machine VSD faults minutes apart

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  
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RE: two identical machine VSD faults minutes apart

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 ?

RE: two identical machine VSD faults minutes apart

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

RE: two identical machine VSD faults minutes apart

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

RE: two identical machine VSD faults minutes apart

Quote (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 ?
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  
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RE: two identical machine VSD faults minutes apart

Quote (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?
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  
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RE: two identical machine VSD faults minutes apart

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.
 

RE: two identical machine VSD faults minutes apart

(OP)
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.
 

RE: two identical machine VSD faults minutes apart

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."

RE: two identical machine VSD faults minutes apart

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.  

RE: two identical machine VSD faults minutes apart

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.

RE: two identical machine VSD faults minutes apart

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.

RE: two identical machine VSD faults minutes apart

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/productcatalog/Industrial+Heaters/Component+Heaters/Components+-+Strip++Ring++Disc/OT/model-details.aspx?m=3528
Part number;
129365      OT-817 IRON 240V1P 175W
Or
Web page;
http://www.chromalox.com/productcatalog/Industrial+Heaters/Component+Heaters/Flexible+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

RE: two identical machine VSD faults minutes apart

(OP)
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.

RE: two identical machine VSD faults minutes apart

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

RE: two identical machine VSD faults minutes apart

As I suggested in the other forum where you first posted this, you might also check to see if the VFD you are using as a "motor winding heat" function built in. Many do now.

If not, you can possibly create a control circuit to make use of the DC Injection Braking feature to do the same thing (the MWH feature is actually the same capability with different logic). What you do is create a "2nd motor profile" that you engage when the motor is going to be off for a long time. Use a Smart Relay to call that 2nd profile and to initiate a pulsed "Run" command, with the drive set for a preset speed of 0Hz, for just a second and then turn off again. This triggers the DCIB, which you set for the maximum time it will allow, but set the DCIB current for about 10% of the FLA. Then just recycle the pulsed Run command again after the DCIB times out. If you want, use a temperature sensor to only initiate this system when the temperature is low enough, but that's tricky because its a moving target with varying humidity (and humidity sensors are usually spendy).


"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: Eng-Tips.com Forum Policies  

RE: two identical machine VSD faults minutes apart

No fishing this time (Did that last week in VA mountains), family va-ca, actually headed up to Macinaw Island. As Waross said it dosent take much heat, you only need to keep the internal temp 1 degree higher than external temp to prevent condensation. I have seen some people just throw a drop light in there on a temperory basis (Not with the motor energized of course).

Sounds like you are on top of the testing part, good luck with your new motors and let us know what happened.

P.S. Listen to Jraef's advice on the VFD, he is a wizard at this stuff.  

RE: two identical machine VSD faults minutes apart

(OP)
My fear of the North Compressor not starting this morning was true, After we received our rebuilt motor last night a installed, tested and ran for an entire night, we shut the machines down for a few hour between shifts. When I got to work this morning and attempted to start the North compressor I had the same problem as last Monday, load pop, flash from the front and the drive faulted out. So back out there we go to pull a second motor off and sending it to the shop to be rebuilt. "So this is what hell looks like!!"

2571

RE: two identical machine VSD faults minutes apart

(OP)
Just to be clear the new motor and compressor is running fine, My post read like it was the same machine we just fixed. Remember I had the same faults on both machines but was able to get the North machine up and had not turned it off all week until last night. I'm really considering adding some liquid brave to my coffee this morning.

2571

RE: two identical machine VSD faults minutes apart

Did you get a failure report from the rewind shop on the first motor ?

RE: two identical machine VSD faults minutes apart

(OP)
Not in hand or on paper, they claim the insulation is what failed. When they performed the their surge test they pick up cross talk from wye to wye at 2000v. Does that help?

2571

RE: two identical machine VSD faults minutes apart

What do they mean by wye to wye ? A surge test checks the turn-to-turn insulation and phase to phase insulation. So, if I assume the motor is wye connected, you would see different ringing patterns on the scope between the failed phase and the healthy phase.

wye to wye ? cross-talk ? Thye should be clearer.

RE: two identical machine VSD faults minutes apart

We tend to have more problems with a rising temperature than a falling temperature. When the temperature is falling, the motor core tends to be warmer than the ambient. The deadly part is in the morning when warm moist air may drift in while the motor core is still cool.

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

RE: two identical machine VSD faults minutes apart

By the way, anti-condensation heaters are often connected at 50% of rated voltage. Either 120V to a 240V rated heater or two 120V heaters in series on 120V. They last almost forever.

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

RE: two identical machine VSD faults minutes apart

A good upkeep policy could help! On my other life, there is a standing order never to run units that were on standby for more than 6 hours. Techs should megger all standby units and put PAR lamps if they'd catch low insulation windings! On a small sheet of paper, techs sign-off every unit for clearance to operate. Simple but cost-effective.

RE: two identical machine VSD faults minutes apart

I find it unusual the VFD is tripping on current fault (error 1) and not Earth Fault (error3). Insulation failures in motors should typically indicate error3.

Another point. When a VFD trips on something as serious as current fault; I would check out the load, the motor, connections, etc before simply resetting the VFD and trying again. Faults in VFD's are there for a reason and had there been a major issue relating to a current fault, then resetting the VFD could create bigger problems with the VFD-i.e. bang!
 

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