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NST core removal progress

Original poster: "M G" <gt4awd@xxxxxxxxx>

Hello everyone, for a while now I have been working on removing a NST core from its case. This was a NST that I was able to get for just the cost of shipping, and is a warrantied NST meaning it has some core issues. Most likely cause of the slightly lower than average output on a jacobs ladder is internal carbon tracking. I did get two NST at the same time. They are both 15kv 30ma Fraceformers, but the second one only makes a slight hum when powered. The first process I used to start the removal of the tar was the heating method. One of the insulators had broke off during shipping, and this gave a convenient area for the tar to slowly seep out of.

The heating process took over five hours because I had started the temperature at only 220F. After nearly two hours in the tar was barely even soft! . I slowly upped the temperature until 310F. (Yes thats right, I used my oven. Decided if it got too messy, started to smell bad, or smoke, I would just cut the heat, and head out to the grill. It worked fine, other than a slight tar smell, and a tiny mess from scooping tar out with a spoon.) At this point the tar was seeping out of the broken insulators hole at a decent rate. I tilted the opposite side, not draining, up some to aid in getting the tar to seep out of the insulators hole.

The problem is I had to cut short the heating process and attend to other matters. So I was never able to remove the core from the case. I had attempted it and it would not budge. Most likely not heated up enough, or just too much tar left. After that I started soaking the NST in Kerosene. After two weeks of the core still not wanting to budge I decided to pull it out of the kerosene, and let it dry out. The core is mostly dried now, and only about 20% of the tar remains. Most of it l! ocated under the core, and on the core to case side with least length.

Today, being that the tar was mostly dry, I decided to remove the insulators, and low voltage connections. After this I used the Dremel tool with grinding pad to cut down the edges of the frount side of the NST case. By the way, if you look at a NST case you can see that one edge seems as if it can be spliced in two with a chisel and hammer. This might be true with a really good and sharp chisel, but did not work out in my case. Why? There is about three very thick welds attaching these two pieces, and because of this I had to grind both sides off in order to bend the side down, and away from the core.

What would you suggest I do from here to safety remove the core?

Matt G.

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