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.

 

[jraef]

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

 

[Zogzog]

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.

 

[2571]

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

 

[2571]

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

 

[edison123]

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

 

[2571]

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

 

[edison123]

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.

 

[waross]

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

 

[waross]

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

 

[burnt2x]

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.

 

[ozmosis]

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!