You see two leads for this transformer. The one on the right is hotter below the bolted connection. It looks like that is an insulated lugged connection from the transformer manufacturer.

There is something a little strange about the thermal pattern of both of those transforme3r lugs (left and right) - hottest around the outside and doesn''t seem to come from one particular part of the connection. What causes that?

Also I don''t quite see the evidence of tailing off on the conductor going up that I expect.

Is it a bad connection at the right-side transformer manufacture''rs lug, or is there something else we should look at?

I wouldn't call myself an expert but I agree, it does not look like a simple poor connection. Looks rather as a reflection because hot spots are being seen only on the spherical and edge portions of the lug (you probably guessed the same but apparently it is hard to block it off).

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

You are probably right that reflection is a big part of the puzzle. I would have liked to have been there to observe the effect of moving the camera, but I wasn’t, and the equipment is now deenergized.

There are hot transformers to the right which can be a source of reflection for low-emissivity surfaces or actual heating for all surfaces.

The insulation below the bolted connection is something like varnished cambric cloth. It has a shiny finish, so it seems possible it may be low emissivity and maybe reflecting off of the hot transformer to the right gives the higher temperature on right side of both the left and the right varnished insulating cloth.

The equipment is now deenergized and cloth insulation has been removed below the right bolted connection. Photo’s of that removed insulation are attached, along with several wider views of the panel.

I’m still trying to piece together the rest of it. Even allowing for reflection and possible some real heating coming from the right, it still seems to me that the right conductor is actually hotter (do you agree?). In a single-phase component I think I can rule out current unbalance so I am still suspecting some other source of heat. But there is no real tail-off to point in any direction. Any ideas?

INVERTER_TRANSFORMER.ppt (1,215 Kb, 45 downloads)

I don't suspect reflection. The material does not appear to have high
reflectivity. If there was a source of reflection, you'd more likely see
that on the side of the shiny nuts and bolts.

I suspect that the source of heat is the crimp under the unsulation, and
that the insulation has areas of good thermal contact with the crimp, and
other areas of air pockets. The air pockets thermally insulate the
electrical insulation from the source of heat, and thus appear cooler.
There is definitely higher temperatures on the wire as it goes up as
compared to the adjacent wire.

I would be concerned about the crimp. Hard to tell just by looking at
these pictures, but that would be my suspicion.

Hope that helps.

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

I had the chance to examine the varnished material closely. If I waved my hand behind it I could see the thermal reflection in it. Defintily low emissivity / high reflectivity.

But I agree reflection is not the whole story and there is some a heat source in that phase somewhere.

I agree with Rich That the heat contours of the connection seem to be associated with the area of contact between the insulation and the conductor.
There is no Conductive heat path, the entire conductor seems to be the same temp above the lug, typically indicative of a load issue. So we are left with how a single phase system could have different heat indicated on input or output:

Is there a load in the transformer... i.e., a high resistance point?
Do an MCE on the transformer..or at least a Megger

Is there a difference in the emmisivity of the insulation of the 2 conductors above the lug? Grease on one, or something like that?

Hmm, having second thoughts..
Are these lugs on the primary or secondary?
If the heat was coming from the windings of the transformer, there should be a heat path.. so it must be load related.

Maybe the tranformer is inefficient, maybe the insulation in the windings has degraded on the load side, causing the load side to have higher heat?
I don't know, this is an interesting one Pete!

Is the Hot side the load side?