I could use some help on an anomaly detected during a routine inspection. The attached thermal image is a stress cone with the same warm spot for two years now. An electrician claims there is nothing wrong. The ultrasound did not pick up any sound what so ever of potential discharge. There does not appear to be any connections in this area that I am aware of, I have never taken these components apart to study so I am lacking in why it is what it is. any thoughts would be geatly appreciated.

Craig Casler

Is it a feeder or bus bar? What is the material & its spec? Will it stands that hotspot for long time? I thought hotspot cause thermal stress concentration around it.

A stress cone is associated with connection from a shielded cable to an unshielded termination/bushing.

If you just abruptly cut the shield, you would have a sharp concentration of electrical stress at that "sharp" corner. Stress concentration is supposed to gradually change the electrical stress profile.

I can't say I have ever surveyed a stress cone. But I sure don't like the looks of your image and would investigate further.

Is there anything externally visible at the point of the hot spot on the image? If a metal strap at that location you might be seeing reflection. If discoloration that would of course be bad news.

From what I have been told the connection of the wire is below the stress cone. The surface has a high emissivity. Not much chance of reflection I did think of that and tried several angles. I have not gotten close enough to look at visually for obvious reason. I will have to get a good digital image with a light. I have a 12 mega pixal digital camera I use for long distance work that way I can get closer look with out getting closer. Here is the original digital image if it helps.

Craig

Somewhere inside of that thing is a splice connecting the two conductors together.

If this is a drawlead type bushing (as opposed to bottom connected), maybe it is possible that the lead is drawn up through the bushing comes out of that porcelain into the stress cone and extends all the way to be spliced/connected in the vicinity where you show the hotspot? In that case a bad splice is causing your hotspot and needs attention.

The only other scenario I can see for producing heat would be something to do with abnormally high leakage currents between conductor and ground at the point of highest electric field intensification... if unusually high might cause heating. An even worse scenario (also probably less plausible).

Personally, I can't think of any scenario where a hotspot such as this could be considered harmless.

Thank you

Craig

Ok, mechanical people call this stress cone as reducer for piping or vessel size changes.