150 HP Air compressor breaker trips

[Davebones]

We have a Atlas Copco GA110 (150 hp ) air compressor installed in 1997 . Our supervisor went to start the compressor the other day and the motor shorted out . As he said he knows this is the 2nd time he's known ( not sure how many times before its seen a short ) of a short in the motor I have a concern about the breaker " LH36300 300 amp " feeding it . Know that they are only rated for so many hard shorts . Right now there is only a 200 amp ( 125 hp rated ) non-fusible disconnect at the compressor . I started to look at changing the non-fusible disconnect to a fusible disconnect with the idea we could coordinate the fuses to go before the breaker trips . I noticed that the wire from the breaker to the disconnect is only 3/0 . I know for a 150 hp the disconnect need's to be at least 400 amp and the wire should have been 4/0 . Being this was done in 1997 and has been running this way should we consider upgrading the wire and disconnect ??

 

[JFletcher]

What are the actual FLA of the machine? Standard motor charts show 150HP 180A @ 480V, and 4/0 cu is good for 230A... even 4/0 AL is good for 180A, so unless it's 3/0 Al, the wire is sized ok*. How long a run to the panel? Yes, the disco is too small, i dont know about coordinating fuses with the breaker; even if the fuses are a lower amperage, there is no guarantee they would blow before the breaker trips with a high fault current.

Have you ruled out the normal suspects like poor maintenance, low oil, particulates getting past the filter, *long run causing excessive voltage drop, low voltage at the panel, higher than designed for ambient temperature, etc.?

 

[kwired]

Is this across the line started, reduced voltage starting method, or VFD driven ?

 

[MrJLH]

We have a Atlas Copco GA110 (150 hp ) air compressor installed in 1997 . Our supervisor went to start the compressor the other day and the motor shorted out . As he said he knows this is the 2nd time he's known ( not sure how many times before its seen a short ) of a short in the motor I have a concern about the breaker " LH36300 300 amp " feeding it . Know that they are only rated for so many hard shorts . Right now there is only a 200 amp ( 125 hp rated ) non-fusible disconnect at the compressor . I started to look at changing the non-fusible disconnect to a fusible disconnect with the idea we could coordinate the fuses to go before the breaker trips . I noticed that the wire from the breaker to the disconnect is only 3/0 . I know for a 150 hp the disconnect need's to be at least 400 amp and the wire should have been 4/0 . Being this was done in 1997 and has been running this way should we consider upgrading the wire and disconnect ??

Is this motor fed from a MCC? If so, and if you can justify pulling the entire bucket out off the MCC live send it out to get it tested at a NETA certified shop.

Are you sure the motor shorted out? Did you confirm with a MCE test? I had the same issue with a pump and the breaker failed due to an earlier single phasing issue from the utility. It was quicker and easier to pull and replace the entire MCC bucket.

As far as your wire size, I have a similar issue. I want to get the system re-fed but my organization is willing to live with the risk as the higher ups wont let me spend the money on such a feat. Remember to that your cable may need further de-rating due to breaker lugs.

The "150Hp" is that the rating of the compressor or the nameplate off the motor? You may have a de-rated motor.

 

[kwired]

Our supervisor went to start the compressor the other day and the motor shorted out . As he said he knows this is the 2nd time he's known ( not sure how many times before its seen a short ) of a short in the motor

A short in the motor would have required repair/replacement the first time around before it would run again. Need more details of what he is calling "short".

Is a chance nothing is wrong with motor and it is just close to magnetic trip point when starting, and occasionally will cross that magnetic trip point when conditions are just right.

 

[Besoeker]

A short in the motor would have required repair/replacement the first time around before it would run again. Need more details of what he is calling "short".

Is a chance nothing is wrong with motor and it is just close to magnetic trip point when starting, and occasionally will cross that magnetic trip point when conditions are just right.

Or just wrong..........
Frivolity aside, I agree. Need more details

 

[texie]

A short in the motor would have required repair/replacement the first time around before it would run again. Need more details of what he is calling "short".

Is a chance nothing is wrong with motor and it is just close to magnetic trip point when starting, and occasionally will cross that magnetic trip point when conditions are just right.

I agree. And if this is truly a standard 150 HP motor with 150 HP of load starting across the line then the breaker is way to small for most applications. I'd be surprised if a 300 amp breaker would start a 150 HP motor with no load on a reliable basis.

 

[Jraef]

Motor shorted twice is something that would concern me more than anything else here. It's either under sized for the compressor, or there is something seriously wrong.

But do you know for SURE that the motor is actually bad? A common issue with compressors is that the unloader valve sticks closed and when that happens, it's almost like trying to start the motor into a locked rotor, so the breaker trips. If you call a motor shop with no ethics, they will tell you what you want to hear, rewind it needlessly to make their money, then offer to re-install it, at which time they fix the unloader valve. I know this from experience...

 

[MrJLH]

Motor shorted twice is something that would concern me more than anything else here. It's either under sized for the compressor, or there is something seriously wrong.

But do you know for SURE that the motor is actually bad? A common issue with compressors is that the unloader valve sticks closed and when that happens, it's almost like trying to start the motor into a locked rotor, so the breaker trips. If you call a motor shop with no ethics, they will tell you what you want to hear, rewind it needlessly to make their money, then offer to re-install it, at which time they fix the unloader valve. I know this from experience...

What he says.

I had a similar issue to one of my compressors last year but it was with the turn valve. The compressor would load and unload causing huge spike in current and would trip the circuit breaker. Turned out it was the regulator which controls the turn valve.

 

[retirede]

Motor shorted twice is something that would concern me more than anything else here. It's either under sized for the compressor, or there is something seriously wrong.

But do you know for SURE that the motor is actually bad? A common issue with compressors is that the unloader valve sticks closed and when that happens, it's almost like trying to start the motor into a locked rotor, so the breaker trips. If you call a motor shop with no ethics, they will tell you what you want to hear, rewind it needlessly to make their money, then offer to re-install it, at which time they fix the unloader valve. I know this from experience...

This is an oil flooded rotary screw compressor. The inlet valve has to close on shutdown and remain closed otherwise it pukes oil out of the air filter. The compressor is unloaded by bleeding off the pressure from the air/oil reservoir. The inlet valve on this type of compressor will not cause a loaded start. If the tank is not depressurized completely, you will have problems when starting. There is normally a pressure switch to prevent starting with a pressurized tank - usually set around 5 PSI. That is where I would begin the investigation, mechanical-wise. Specifics about the motor failure would be most helpful as well.

 

[Besoeker]

We have a Atlas Copco GA110 (150 hp ) air compressor installed in 1997 . Our supervisor went to start the compressor the other day and the motor shorted out . As he said he knows this is the 2nd time he's known ( not sure how many times before its seen a short ) of a short in the motor

Does the motor actually have a hard wired physical short. i.e. physically damaged windings each time?
Sparks, or at least smoke let out?

 

[Davebones]

When they went to start the compressor they said they heard a "BOOM" . Motor was shorted to ground we verified that with a megger and it even read to ground with a ohm meter . This is across the line started with the feed from the 300 amp breaker about 150 ft away in a Sq D 1600 amp switchboard . The motor ( TECFC 150 hp ) has already been sent out for repair so I can't verify actual name plate amps right now . This is a Atlas Copco packaged air compressor inside a stand alone enclosure and has been running like this since 1997 . If I was asked to install this from scratch I would install a 400 amp fusible disconnect at the compressor with 4/0 feeds to it . Just mainly concerned as this is second short I know of for this breaker and I saw wire is 3/0 not 4/0 . Know its been running like this for years is a upgrade what most would do ?

 

[drktmplr12]

When they went to start the compressor they said they heard a "BOOM" . Motor was shorted to ground we verified that with a megger and it even read to ground with a ohm meter . This is across the line started with the feed from the 300 amp breaker about 150 ft away in a Sq D 1600 amp switchboard . The motor ( TECFC 150 hp ) has already been sent out for repair so I can't verify actual name plate amps right now . This is a Atlas Copco packaged air compressor inside a stand alone enclosure and has been running like this since 1997 . If I was asked to install this from scratch I would install a 400 amp fusible disconnect at the compressor with 4/0 feeds to it . Just mainly concerned as this is second short I know of for this breaker and I saw wire is 3/0 not 4/0 . Know its been running like this for years is a upgrade what most would do ?

Hire NETA testing firm to test the breaker and certify if operation is within spec.

edit:

I would consider it a fire hazard left as is. I would replace with 4/0, as you suggest. This is assuming money is not an issue. 600 feet of 4/0 isn't cheap and it might be hard to justify to management why it should be replaced if it's been that way for decades.

Compressor motors take a beating, but I have seen 25 year old compressors still running, continuous duty (charging a tank).

 

[kwired]

When they went to start the compressor they said they heard a "BOOM" . Motor was shorted to ground we verified that with a megger and it even read to ground with a ohm meter . This is across the line started with the feed from the 300 amp breaker about 150 ft away in a Sq D 1600 amp switchboard . The motor ( TECFC 150 hp ) has already been sent out for repair so I can't verify actual name plate amps right now . This is a Atlas Copco packaged air compressor inside a stand alone enclosure and has been running like this since 1997 . If I was asked to install this from scratch I would install a 400 amp fusible disconnect at the compressor with 4/0 feeds to it . Just mainly concerned as this is second short I know of for this breaker and I saw wire is 3/0 not 4/0 . Know its been running like this for years is a upgrade what most would do ?

Well if you did have a ground fault then the breaker responded as it should. There could be concern over whether the fault caused some damage to the breaker, but the breaker certainly did not cause the ground fault.

Only slightly undersized conductor didn't cause the ground fault either, if anything it helped reduce starting current, sort of like a soft starter would.

Things to check for if you are burning out motors frequently:

make sure motor isn't overloaded, proper application and selection of overload protection should catch things that you maybe missed because you didn't check load at the right time.

make sure it is being properly cooled.

bad bearings can also contribute to heat within the motor

even if motor isn't mechanically overloaded, excess heat is still a problem that will break down insulation over time.

 

[retirede]

These compressors are designed to pull 10% over nameplate, utilizing 10 of the 15% service factor. This results on shorter motor life. Now throw in any voltage issues (imbalance or low voltage) and higher ambient temperatures, you can get much shorter motor life.

 

[topgone]

When they went to start the compressor they said they heard a "BOOM" . Motor was shorted to ground we verified that with a megger and it even read to ground with a ohm meter . This is across the line started with the feed from the 300 amp breaker about 150 ft away in a Sq D 1600 amp switchboard . The motor ( TECFC 150 hp ) has already been sent out for repair so I can't verify actual name plate amps right now . This is a Atlas Copco packaged air compressor inside a stand alone enclosure and has been running like this since 1997 . If I was asked to install this from scratch I would install a 400 amp fusible disconnect at the compressor with 4/0 feeds to it . Just mainly concerned as this is second short I know of for this breaker and I saw wire is 3/0 not 4/0 . Know its been running like this for years is a upgrade what most would do ?

I think they missed to take the insulation resistance of the compressor motor before they started the compressor. In my other life, working in a very old power plant, we always make sure all motors that had been standing by for 8 hours to be tested prior to starting.

The breaker just did what it has to do, isolate a faulty equipment. The 300A CB rating is just fine with a 150 hp motor (fla=165), IMO.