I have a painted support structure inside of a main bus getting a reading of about 85-90 C. The bus is copper clad, so I don't know its exact emissivity. Depending on Corrosion, it can be from .78 corroded to .02 for polished. That is a large variable. If the bus is near the same temperature, its' emiss would be about .25
The hot spot in the IR picture is an insulated support structure that has bus running on it on three sides. IT conducts no electricity (verified).

4000 amp breaker running about 1200 amps.

The initial conclusion I have is that we have some loose bus bolts, which are out of view in the center of the bus. The poor connection is radiating heat which can be seen in the painted support structure.

The problem is that I would expect that each of these busses would have roughly equal emmis values, and I should see one of the plates considerably warmer than the rest. The one closest to us is " cooler" but, it is also able to radiate into open space, I would expect it to be cooler.

Does anyone here have some experience with emiss value on copper clad bus?

Bus_heat.doc (550 Kb, 50 downloads)

It's tough to judge copper emissivity directly. But the cavity effect may help you avoid having to do this. Even where you have a very low emissivity material, if you have a cavity, it acts close to emissivity 1.0.

I believe this is a big reason why the outermost bus appears coolest - it has no adjacent bus to reflect from and no "cavity effect". (as well as better cooling that you mention)

I have a hard time recognizing exactly what I'm looking at. But from what I can tell your temperature is fairly uniform on the bus. It looks like you have pairs of bus very close together and the temp in between there is the actual temp... in the nieghborhood 35-40C.

The insulator you mention below appears to be hot for some unknown reason. Not sure about that one.

The apparent double-strip hot spot on the bottom of the horizontal bus section I believe is just a reflection (possibly from that insulator if the insulator is in fact hot). If it were actual heating you would see more of a gradual change away from that area. Likewise similar double-striped hot-spot vertically behind that insulator would appear to be a reflection. These two items I am pretty sure about (that you are just seeing a reflection on these striped-shaped hot spots).

I am less certain about the insulator itself being hot. Wondering if it might be reflecting too. Don't know.

Of course I may be way off base... just telling what I think I see.

This message has been edited. Last edited by: electricpete,

Pete:
This is what I have been thinking too.. but if it is a reflection of something... what could be 85 C to reflect inside a bus? What is the source of 85c?
I considered that this structure might be conducting somehow, but I would think that it would be evenly heated if it was not properly insulated and conducting current

Hey Martin. I was editing while you were typing. I don't know.

The 85C is only on what I think you're calling the insulator... the horizontal structure near bottom of the picture (?). Maybe a light source to the left and behind the thermographer?

Thinking some more, I'm definitely not sure about anything on this one.

The pink double-stripe hot spots I am pretty sure are reflections.

Look carefully and the edges of the buses are pink but the area between is blue.

If it was a real hotspot, we would see the temeprature even hotter between those two plates (in the cavity), but we see just the opposite (cooler betewen the plates).

If it is a reflection, we only see the reflection on the surface which is the proper orientation to reflect from the source. This matches what we are seeing on those pink striped hotspots.

Another thing to notice - the cavity is the real temperature. Look at the cavity to left and right... it is uniform blue. All of this fits together to suggest the bus is uniform temperature.

I agree, the pink stripes are reflections of the support structure.. that is expected.

I'm not sure if the "crevice rule" applies here because of the camera angle on the crevice, it is almost directly at the bus. I am looking through all of my other shots for better angles at crevices.

The highest temp seems to be right in the center of the support structure, mid point of the bus. This would make sense under normal conditions. If this Structure were 40 C, I wouldn't be asking any questions.

But a 90C reading on a structure doesn't manifest itself from nothing.

As strange as a conclusion as this seems... is it possible that this structure is the source, and is being induced? The Bus wraps around it on 3 sides.

Both A side and B side have the same infared signature. B side is at 101C, but it also has a higher load. (200 amps vs 1200 amps.
Rubber Isolators attached to the busses are at 35C.

Also, the Structure closest to the intersection of the buses is the hotest.

Opps, B side is 2000 Amps VS 1200 amps

Martin,

It indeed appears to be that the structural member is the source of heat, due to induction. This is supported by the reflection seen on the sides of the bus bar (the "pink stripes"). The cavity effect has nothing to do with the surroundings. If there is a sufficiently deep cavity in a surface that is an infrared reflector, the apparent emissivity will be greater than the reflective flat surface. This effect can typically be seen also on bolts, either in the groove of the thread, or in the recesses where the nut contacts the bolt. It often isn't enought to make the apparent emissivity the same as a black body, but it can sufficiently improve it to rule out the reflective surface as the source of heating. The uniformity seen across this entire buswork and it's fasteners leads me to believe that there is no significant heating at the bolted connnections.

I've attached a similar highly polished busbar connection that is indeed overheating. Notice that in the sandwich areas and the bolted areas, apparent emissivity improvement is seen due to the cavity effect. Without any such indication in your image, I strongly suspect induction heating in the support. This is further backed up by the uneven loading that you have in the system.

Here is another view of that issue. Notice that the flat portions of the bus do not appear to be heated up, even directly adjacent to hotter areas. But the bolt/nut crevices and the recessed areas where the bars are sandwiched show improved apparent emissivity, and indicate the true heating going on here due to loose fasteners. Again, I don't believe you have this problem, but that you have a strictly induction-heating temperature rise on the support running between the phases, which is quite typical for a lame design such as that.

Rich Wurzbach
ASNT PdM Level III-Infrared and Thermal Testing
Maintenance Reliability Group, LLC
rwurzbach@mrgcorp.com

Could the support structure be hot due to inductive heating from the magnetic fields around the bus. At a plant that I worked at we had copper buses running out to an electric furnace with three 55" electrodes. Some of the structural beams around the buses would heat up to over 500 Deg F.

Rich:
When I wrote "A" and "B" I was not referring to different Phases of the same bus.
I was referring to Two seperate buses with 2 entirely different loads, but the same design.

This lends credance to inductance, since the probability that two different busses have failed in exactly the same way at the same time is not as likely.

I do not know the loads of each phase of each bus.

The thing that is making me a bit uncomfortable about declaring these connections "good" is that I cannont see the bolts on the center bus, which is where the structural element is hottest.
But all of the other data supports the induction theory.
I have reviewed some of my other thermograms with induction in mind, and they all seem to make sense. I can find no conductive paths from any bus connection. (some I can't see)

All:
The other thing that is giving me confidence about induction is that in order to get the support structure to 90C.. how hot would the bus have to be??? I don't know exactly, but obviously with no direct connection, and a distance of 6inches - 1 foot.. the bus would have to be incredibly hot.

Also, if the "B" Phase were that hot... A and C phase should likewise be hot from the radiant heat.. which they are clearly not.

Does all that sound correct to you Rich?

and BTW, Thanks for your assistance.

Rich are you saying Camera angle is irrelevant when it comes to apparent emissivity due to crevices?

Martin,

I'm not saying that camera angle is irrelevant, but rather that the surroundings do not influence the cavity effect. Cavity effect is an "apparent emissivity" phenomenon, where there is an increased emission of energy from a surface that is a substantial reflector, due to the geometry, and the ability of of the portion that is the cavity to emit more radiation than a the adjacent perpendicular, flat, reflective surface. When you have a very effective cavity emitter, which means that there is a hole that is sufficiently deep to give this effect, and a target hole or crevice that is large enough to impact the camera's IFOV, then the cavity emitter site will begin to emit radiation which approaches blackbody characteristics. A blackbody's apparent radiative temperature is not affected by its surroundings. If you introduce too steep an angle of incidence, you will begin to loose the cavity emitter effect. I don't think that is happening anywhere in your image.

Realize too that all of the higher indicated IR radiation seen in you image is at angles that would reflect the structural member. Also, the heat on the structural member is fairly constant along the viewable length. If it were being heated by adjacent bus, then I would expect the area of the structural member closest to that source to be the hottest, and see it cooling as you got further away. Induction will occur in the member in proportion to the strength of the electromagnetic field. I believe that you have induction.

Rich Wurzbach

Maintenance Reliability Group

This horizontal yellow (thermally) insulating support structure. - now I see that it goes behind the vertical section of bus, and we can see its reflection (pink) in front of it on that vertical section of bus. (I was misjudging it before... thought the yellow went in front of the bus and abruptly turned pink... seemed more like a reflection.)

Now that I see what it's doing and that this horizontal insulating support structure is uniformly yellow hot, it makes sense that it is actually hot and not a reflection. Inductive heating definitely seems right.

I would be interested to know what really is the function of that horizontal insulator or whatever it is. Most likely if it is a non-electrical part, it's not going to hurt anything to be that hot. Although you mentioned it was insulated... I would want to understand what is the insulating function and what materials involved to know if they are in danger. For kicks, it may be interesting to see if you can get a clamp-on around part of it to check for insulating currents (with proper electrical safety supervision). We have a handrail near our main generator leadbox which I noticed was hot. I put a clamp-on on there and measured 160A flowing in a loop in the handrail.

But it would seem no concerns on the bus.

This message has been edited. Last edited by: electricpete,

If this is due to induction then try replacing the item with a non-ferrous support. Assuming it is metal in construction then replace it with non-ferrous stainless steel. You will have to check to make sure you wont be introducing any potential problems for yourself first, so run it by the manufacturer.

On the image, it is thermally tuned on the support. I would like to see it thermally tuned on the busbars before ruling out any problems.

Thermal Vision

bob@thermalvision.ie

Here are some other shots

Additional_data.doc (1,211 Kb, 30 downloads)

Now I see what should have been obvious before to me before – this insulating support structure is supporting the bus itself (duh).

So one danger is if that heating destroys the insulating capability of the coating on that insulating support structure and exposes the underlying metal to act as a short circuit from bus to ground.

If during maintenance periods, a maintenance level hi-pot test to ground is performed on the bus (with the support obviously always at gound), that would help to confirm that the insulation function of the coating is not close to breaking down. Also some visual inspections would help.

Getting rid of the heating would be even better if you can do it as was mentioned above. There are two mechanisms for heating: hysteresis in magnetizeable steel materials, and circulating currents. It's not clear to me which is going on. (although maybe someone else can clarify). If you get a chance during shutdown, check the support structure with a magnet. Also try clamp on ammeter through some of those holes while energized (while observing safe distances to the bus) and check for evidence of circulating current. Depending on circulating current path, sometimes inserting an insulator in the loop (while still maintaining both sides grounded) fixes circulating current.

What is the voltage of the system.