what a monday

[LHarrington]

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.

LHarrington

 

[ptonsparky]

Do your drives have an option for Ground Fault detection that has been disabled? I would have thought this option would have picked up before an overcurrent fault if we are looking at insulation values due to humidity.

I am not familiar with this large of compressor system but were they trying to start against high head pressure?

 

[76nemo]

Just how old are these motors????

 

[hurk27]

Do your drives have an option for Ground Fault detection that has been disabled? I would have thought this option would have picked up before an overcurrent fault if we are looking at insulation values due to humidity.

I am not familiar with this large of compressor system but were they trying to start against high head pressure?[/QUOTE]

Sullair compressors are a Screw compressor, not a reciprocating, there is no head pressure, with a VFD driven one I would say less than 10 years old.

My uncle started the company with Don Hoods back in the late "60s"

The company was bought out by Sunstrand Corp, but is still about 15 miles from me in Michigan City, In.

 

[mcclary's electrical]

I was called to a lumber yard for a 150 Gardner Denver compressor. The machine kicked breaker at start up monday,,,,they reset and tried again. The motor went phase to phase short sparks flew. Come to find out they had pressure washed the compressor that saturday,,,,without covering the motor,,,,,wooops

 

[Jraef]

Motor winding condensation is a big problem in some areas to be sure. But for it to happen, you need a specific set of circumstances; high relative humidity followed by cool relative temperatures, i.e. below the "dew point" for the humidity and barometric pressure. Most weather services will offer that information if you ask, but it's not something that the average weather girl tells you on the evening news. The thing is, the higher the relative humidity, the higher the dew point, so if you have 90% RH, your dew point can be as high as 90 degrees F! (that's why I said relatively cool temps). Unfortunately, this is something that does happen quite a bit in the Southeast US.

Some VFDs provide a feature called a Motor Winding Heater function. What it does is that it puts a low level of controlled DC current on the motor when it is off; just enough to keep the motor windings warmer than the surrounding air. It doesn't harm the motor and can prevent this sort of thing. If your VFDs don't do that, see if they have a feature called DC Injection Braking (most do). With a little trickery, you can use that feature ot accomplish the same thing. It's a lot trickier that way, but on some drives its the only way.

You can also add strip heaters to the motors to do the same thing. The trouble is, you have to run new conduits etc., because they can't be powered by the same motor conductors. This can get expensive on a retrofit.

There are also separate Motor Winding Heaters that act just like the VFD feature, but they are usually used when there is no VFD, because using them with a VFD involves some expensive interlocked contactors to prevent them from being in the circuit at the same time as the VFD.

See what you have available to you, then post what you have for more help on how to implement it.

 

[LHarrington]

Do your drives have an option for Ground Fault detection that has been disabled? I would have thought this option would have picked up before an overcurrent fault if we are looking at insulation values due to humidity.

I am not familiar with this large of compressor system but were they trying to start against high head pressure?

yes we do have Ground fault detection and it is enabled

 

[LHarrington]

Just how old are these motors????

Just three years old, everything is covered under Wegs warrenty thus far with the exception of my lack of sleep and heartburn.

 

[LHarrington]

I was called to a lumber yard for a 150 Gardner Denver compressor. The machine kicked breaker at start up monday,,,,they reset and tried again. The motor went phase to phase short sparks flew. Come to find out they had pressure washed the compressor that saturday,,,,without covering the motor,,,,,wooops

I thought I had wet motors and/or drives as well but there were no sign of water any where on the motors, floor etc... We had a problem last spring when our roof leaked directly into the drive of the same machine that blew the motor but that drive was replace and corrections to the roof and the tops of the drives were take to ever prevent this from happening.

 

[LHarrington]

Motor winding condensation is a big problem in some areas to be sure. But for it to happen, you need a specific set of circumstances; high relative humidity followed by cool relative temperatures, i.e. below the "dew point" for the humidity and barometric pressure. Most weather services will offer that information if you ask, but it's not something that the average weather girl tells you on the evening news. The thing is, the higher the relative humidity, the higher the dew point, so if you have 90% RH, your dew point can be as high as 90 degrees F! (that's why I said relatively cool temps). Unfortunately, this is something that does happen quite a bit in the Southeast US.

Some VFDs provide a feature called a Motor Winding Heater function. What it does is that it puts a low level of controlled DC current on the motor when it is off; just enough to keep the motor windings warmer than the surrounding air. It doesn't harm the motor and can prevent this sort of thing. If your VFDs don't do that, see if they have a feature called DC Injection Braking (most do). With a little trickery, you can use that feature ot accomplish the same thing. It's a lot trickier that way, but on some drives its the only way.

You can also add strip heaters to the motors to do the same thing. The trouble is, you have to run new conduits etc., because they can't be powered by the same motor conductors. This can get expensive on a retrofit.

There are also separate Motor Winding Heaters that act just like the VFD feature, but they are usually used when there is no VFD, because using them with a VFD involves some expensive interlocked contactors to prevent them from being in the circuit at the same time as the VFD.

See what you have available to you, then post what you have for more help on how to implement it.

I will look into this option by consulting the manufacture of the drive and the compressor to see if it is an option. I would assume it is, because these units can be put outside if you purchase the weather package which includes canopies, side wall and several other options. I will also ask out local weather to provide me with the weather conditions you had mentioned.

Thank you everyone for you help thus far.