400A breaker heating up and tripping

[A1b5c0pe1984]

Hello all,

This is my first post on here, though I have read it many times and it has helped me troubleshoot problems throughout my career. I am currently at the end of my rope on a troubleshooting issue I'm having with a 400A breaker tripping.

This problem has persisted for quite some time. It first showed on an old Motor Control Center (MCC) from probably the 1960s. It was hooked up to an older transformer and would occur periodically over the last two years. The head of maintenance at that location got tired of dealing with it (because when it tripped it would make a giant mess of things in the plant) so he switched the feed of that MCC to a newly installed transformer with a new Main Distribution Panel (MDP) and brand new 400A breakers (hjxd63b400) in hopes that this would fix the problem. It did not and the same thing would occur. It will work for days/weeks/months and heat up and trip. As luck would have it, they are completely redoing this plant and this is when I got involved. In order to redo this plant, we had to get rid of the old MCC in order for us to put one of our new panels in. We already had a Motor Control Panel (MCP) installed because we have done some automation there, with two 400A feeds inside of it. This panel is mostly comprised of FVNR AB starters with E300 overloads on each one. The starters are hung directly on the busbar with a mount that goes to the starter and from there gets passed to the individual motors. When we moved the starters, we split up the trouble MCC from one feed to the other to help try to narrow this down. In doing this we found more problems but that is neither here nor there. Now this issue is showing up on a different breaker in the MDP from when it was hooked up originally as the old MCC.

Things they have tried:
Changing the breaker twice.
Changing the location the breaker is on the MDP.
Megged all leads. Line and motor.
Torqued all fasteners to factory recommendation.
Thermal imaging of the breaker shows the heat originating at the breaker and going to the wires, but gets less hot as the wire leaves the breaker.

Things I have tried:
Put a power analyzer on to check all conditions.
Installed an PowerMonitor 5000 to double check the power analyzer (and store the data).

I was thinking this could be a harmonics issue, but everything that I have recorded tells me it is not.
I am under 3% in all of my harmonic readings.
Current imbalance sits around 3% (have read if you get close to 10% it becomes an issue).
Voltage imbalance is less than .5%.
Power Factor is low around 52% but I wouldn't think that would do this, but I could be wrong.

I am only pulling around 140A continuous on all phases (A phase is a little low, 135A)
I have have been watching A, B and C phase currents from all the motors. The only odd thing I see is a single phase's amps (all A, B or C phase) will jump slightly on all motors at the same time throughout the system. All three phases do this. I don't know if this is a problem or the system correcting itself. Any help would be appreciated.

-Ben

 

[jim dungar]

You need to record what your post system is doing. Nothing else is worth doing on a non regular issue.
If you can't replicate the condition causing the trip how would you know you have solved the issue.

 

[A1b5c0pe1984]

You need to record what your post system is doing. Nothing else is worth doing on a non regular issue.
If you can't replicate the condition causing the trip how would you know you have solved the issue.

I am currently recording everything from the PowerMonitor 5000 and graphing it in an HMI software which stores the data. There is nothing odd happening when the breaker trips from what I can tell, amps and volts stay the same along with all the harmonic and power factor readings until it trips. But the breaker is getting hotter and will eventually trip.

 

[A1b5c0pe1984]

To clarify, it is coming from a 1200A MDP. And only this breaker is heating up on that system.

 

[jim dungar]

Thermal magnetic breakers trip based on heat.
Fully loaded breakers actually run quite hot. Their trip point relies on the ambient temperature as well as the heat sink provided by the conductors and enclosure ventilation.

If you are not near full load, your harmonics would be the next thing I would look at. Look at the content and not just the THD.

Anecdotally, I had one instance when a protective device would operate fairly often. It turned out that the hot air from a backup compressor was being vented directly at our enclosure.

 

[CoolWill]

What is the ambient temperature and are there comparable loads on other breakers that are not tripping?

 

[A1b5c0pe1984]

Thermal magnetic breakers trip based on heat.
Fully loaded breakers actually run quite hot. Their trip point relies on the ambient temperature as well as the heat sink provided by the conductors and enclosure ventilation.

If you are not near full load, your harmonics would be the next thing I would look at. Look at the content and not just the THD.

Anecdotally, I had one instance when a protective device would operate fairly often. It turned out that the hot air from a backup compressor was being vented directly at our enclosure.

The ambient temp can be anywhere from 50 degrees F to I would say tops 90 degrees F (and it has tripped at the lower temps). This breaker was tested at 104 degrees F so it should be ok. When we had the power analyzer hooked up to the breaker, we could see the harmonics broken down by 3rd, 5th etc. There were little to none on it. I was told they had another electrical engineer who was a PE come in, and his final breakdown was that it was textbook harmonics without harmonics. There aren't any VFDs or PFCs on this breaker, just motors differing in size.

I wouldn't think this would get hot enough to trip with just 140A on it without something else going on.

I appreciate your thoughts.

 

[A1b5c0pe1984]

What is the ambient temperature and are there comparable loads on other breakers that are not tripping?

Ambient temp can be anywhere from 50^oF to 90^oF. Yes, there are two other identical breakers that run motors (VFDs and soft starts) One has around 160A and the other around 100A. There have been no problems with these two breakers on the same 1200A MDP.

 

[A1b5c0pe1984]

The ambient temp can be anywhere from 50 degrees F to I would say tops 90 degrees F (and it has tripped at the lower temps). This breaker was tested at 104 degrees F so it should be ok. When we had the power analyzer hooked up to the breaker, we could see the harmonics broken down by 3rd, 5th etc. There were little to none on it. I was told they had another electrical engineer who was a PE come in, and his final breakdown was that it was textbook harmonics without harmonics. There aren't any VFDs or PFCs on this breaker, just motors differing in size.

I wouldn't think this would get hot enough to trip with just 140A on it without something else going on.

I appreciate your thoughts.

Also, there are no PFCs on this transformer, though there are a few VFDs controlling smaller HP motors.

 

[A1b5c0pe1984]

Ambient temp can be anywhere from 50^oF to 90^oF. Yes, there are two other identical breakers that run motors (VFDs and soft starts) One has around 160A and the other around 100A. There have been no problems with these two breakers on the same 1200A MDP.

To clarify this, it is still mostly FVNR starters on these other two breakers. But there are a few VFDs and soft starts.

 

[MidwestJest141]

Spit balling here. Is there parallel feed coming into the breaker? Are the phases separated in separate conduits? Do you have all phase a conductors in one conduit and all b in one conduit etc. Magnetic field heat generation due to same phases within magnetic conduits has in our experience created major heating issues. We had switchgear that had major heat issues because we combined phases in the same conduits and pass throughs in the enclosure that created massive heating issues. We had to redo all the feeders into the enclosure and that solved our heating issues on the main breaker. Some one much smarter than me will hop in shortly to shoot down my point or help it along.

 

[A1b5c0pe1984]

Spit balling here. Is there parallel feed coming into the breaker? Are the phases separated in separate conduits? Do you have all phase a conductors in one conduit and all b in one conduit etc. Magnetic field heat generation due to same phases within magnetic conduits has in our experience created major heating issues. We had switchgear that had major heat issues because we combined phases in the same conduits and pass throughs in the enclosure that created massive heating issues. We had to redo all the feeders into the enclosure and that solved our heating issues on the main breaker. Some one much smarter than me will hop in shortly to shoot down my point or help it along.

There are parallel feeds feeding the panel. But each conduit has all 3 phases in each.

 

[zbang]

Power Factor is low around 52% but I wouldn't think that would do this, but I could be wrong.

So could I, but that's mighty low. Have you tried some temporary PF correction? (What are the loads driving the PF down?)

 

[A1b5c0pe1984]

So could I, but that's mighty low. Have you tried some temporary PF correction? (What are the loads driving the PF down?)

I have not. Honestly after all of this I was not sure what direction to even go in. That would be fairly easy to accomplish though.

 

[A1b5c0pe1984]

So could I, but that's mighty low. Have you tried some temporary PF correction? (What are the loads driving the PF down?)

They are FVNR motors that are by my best guess oversized for the application.

 

[d0nut]

So, to summarize:

1. You had a 400A breaker feeding an MCC that was tripping.
2. You moved the MCC feed to a different breaker in different distribution equipment and that breaker started tripping.
3. You split the load from the MCC onto two different breakers via the MCP, and now another breaker in the MDP is tripping.

Was some of the load that was in the MCC previously being fed from the MDP breaker that is now tripping?

 

[A1b5c0pe1984]

So, to summarize:

1. You had a 400A breaker feeding an MCC that was tripping.
2. You moved the MCC feed to a different breaker in different distribution equipment and that breaker started tripping.
3. You split the load from the MCC onto two different breakers via the MCP, and now another breaker in the MDP is tripping.

Was some of the load that was in the MCC previously being fed from the MDP breaker that is now tripping?

Your summerization is correct.

No. This was a new feed with a new breaker into the MCP to be able to accommodate more amperage for the upcoming project we are going to be doing. It seems that the problem of the breaker slowly heating up and tripping has followed a certain set of motors. There are currently 12 motors running on this breaker though not all of them are from the original problem MCC. I was thinking about moving half of the motor starters (from the original problem MCC) to the other feed and see if it follows it there, and try to track it down like that, though this way seems painstaking.

 

[d0nut]

I was thinking about moving half of the motor starters (from the original problem MCC) to the other feed and see if it follows it there, and try to track it down like that, though this way seems painstaking.

This is where I was going with my question. If the tripping is following the equipment and persists when you change out the upstream breakers and distribution, then it sounds like it is a load issue. Since it is intermittent, it will be difficult to find, but separating the motors and seeing which breaker trips may let you progress with the troubleshooting without impacting the operation too much. Right or wrong, it may also make things easier with the plant as you will be doing something rather than just looking at meter data and scratching your head. If you can narrow it down to a small amount of equipment, it will be easier to find the issue or perhaps it ends up at the point where you have one bad motor that you just replace rather than finding the exact cause of the tripping.

 

[mtnelectrical]

Your summerization is correct.

No. This was a new feed with a new breaker into the MCP to be able to accommodate more amperage for the upcoming project we are going to be doing. It seems that the problem of the breaker slowly heating up and tripping has followed a certain set of motors. There are currently 12 motors running on this breaker though not all of them are from the original problem MCC. I was thinking about moving half of the motor starters (from the original problem MCC) to the other feed and see if it follows it there, and try to track it down like that, though this way seems painstaking.

Please give us an update on your findings

 

[A1b5c0pe1984]

Please give us an update on your findings

Just got back from the plant. We had to do a little work to the panel to clean it up and get it ready for the project kicking off this winter. We now have a power analyzer on both feeds in that panel, and the power company is going to come and meter their side of it as well. We're also going to look into both transformers this was affecting to essentially cross off any reasons it could be doing this (even though I think this is a specific load issue).

When we had everything shut off, I moved half (4) of the motor starters to a different feed in the panel. About 2 hours after we left (3 hours after they started up), the breaker heated up and tripped on bus bars that I moved the starters to. I directed the head of maintenance to shut everything down again while they were cleaning the plant and move two starters back to their original feed and it has held since Monday around 7 pm. Hopefully with all the equipment we have on it we can catch something. The breaker that tripped had a power analyzer on it, but the company didn't hit the record button so we didn't get any data from it. Suppose we'll see what happens the next time it trips.