The other night something blew up on the utility pole outside my bedroom window (I started another thread about that).
Yesterday, I collected the bits and pieces that I found on the lawn.
My first thought is “insulator”, but that big lump of carbon is puzzling to me.
Why would an insulator have metal contacts on the ends and a big lump of carbon inside. It appears that the carbon fits inside, but it could have come from somewhere else on the pole.
It’s a ceramic insulator. This page has a schematic breakdown of one type. Unfortunately, I do not know what the fill material is and its function. Maybe another more knowledgable doper will be along to explain.
The vote here at the ol power co is we’re looking at pieces of a lightning arrestor used on distribution poles.
The idea is that it acts like an insulator for distribution voltages (12,000 volts) but the carbon filling will form a path for high voltages (lightning) to “bleed” out of the system. It “should” have bled the current surge from the high voltage out and then resumed its job but sometimes the current is so strong that it destroys the arrestor.
Think of it like a spillway on a dam. It is built in such a way that the water is held back, but too much water and it lets it out. It then goes back to normal levels. Overstress a spillway though and it could breach the dam.
My guess is that either lightning struck the line somewhere close by or wind,ice, snow caused a high voltage transmission line (69,000 - 500,000volts) to come into contact with the distribution line.
That was my guess as well.
We actually talked it over. In our office are a number of engineers. The “review panel” was two control engineers and a power plant engineer. All of us thought the pieces looked like an insulator (the ceramic wavy parts) but the carbon core indicated a lightning arrestor (which has insulator looking parts).
Again, it looked familiar but no one of us is a true “distribution engineer”. The distribution engineers are in another building, dress even funnier than we do, and would have been happy to provide us with long explanations and pages of pictures and diagrams had we been foolish enough to ask.
I’m consulting my copy of the Electrical Engineer’s Reference Book, which thoroughly covers power distribution engineering. Its description of a surge arrestor closely matches the device in the OP:
You guys are the best!
Now I can toss the whole works in the trash. My wife said nothing when I brought it in the house in a plastic grocery sack, but her look spoke volumes.
Well, if yer gonna cheat and actually look it up in a book. :dubious: 
