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Re potting Magneblast breaker bottles

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Thedroid

Electrical
May 18, 2008
196
What are the recommended materials for re potting GE Magneblast breaker bottles. Ours are showing signs of cracking and seperation between the bar and potting compound. We were smelling ozone, and called in a specialist. He chiseled out the old potting compound re wrapped the bars with silicone tape, and bought some tar from Home Depot to fill the bottle up with. We had a few bus joints that showed signs of partial discharge also. The joints were enclosed within a plastic case tied together with string and filled with a tar like compound. These cases were removed, the bolts retorqued, and were covered with silicone tape. The cases were not reinstalled.

Is there a special compound that should be used, or is roofing tar sufficient? We would like to inspect the bus during our outage, but are unsure whether to use the same contractor.

 
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As I read your post your planning on re-sleeving the bus with Raychem heat shrink tubing, and using Raychem heat shrink tape on the standard joints. This should work well. I hope your also purchased a couple of Raychems torches to do the shrinking. If the bus supports between cells are porceline insure your newly sleeved bus actually fits through it before you go to the trouble of taking the all the bus out. Pre heat the bus bars (hot enough to blister the skin) prior to installing and shrinking the sleeving sleeving. A roofers torch is perfect for that task (but a bit much for the sleeving).

I am not sure I would go to the trouble of re-potting the bottles on 5kV switchgear. Maybe I would pour new compound in the cracks or spaces at best. But we covered all that in earlier posts.

I hope you have small techs with long arms on hand for this project. Please keep us posted and good luck.
 
I recommend you do a corona scan and PD survey right after start up to check your work and establish baseline data.
 
We did order the torch from Raychem. I considered the cons of using the epoxy, but I don't want to have to deal with having to heat up the pine resin and pour it.

 
If you are removing bus and putting on heat shrink sleeving, be careful handling the hot finished product. Don't rush re-installing the sleeved pcs. They will continue to shrink until cool. A small tear when installing hot will result in severely damaged sleeving as it will continue to tear while it shrinks. Remember to pre heat the bus (if sleeving). It makes all the difference. Wrapping the joints with Raychem tape then heating would work perfect. I have never used the sheets.
 
Maybe it is a retrofit Magneblast, the originals had no vacuum bottles. Get a new retrofit or better still replace them with new switchgear and gain a lot of space if two high. This technolgy replaced old filled breakers in the 60S.
 
Definately not a retrofit. No vacuum bottles either. I was refering to the porcelain insulators containing the primary disconnects. I guess the look like "bottles". We recieved the Raychem HVIS for the bolted joints, and also their HV heat shrink tape for the bars themselves. The torch they supplied looks pretty nice. I'll test it tommorow. We're still waiting on the 3M scotchcast resin, but it should be in soon. A skinny tech with long arms would definately be a plus. The plan is to try and do most of the work with the breaker in place, that way we don't lose the alignment. It seems like a daunting job, but hopefully it will keep a few of us in the Electrical dept. working, while most of the plant is on furlough.

 
This seems like a third world solution, patching up 40 year old magnetic air circuit breakers. Get a new circuit breaker, your modifications are not tested or certified and could result in an accident.
 
He is repairing the switchgear, not the breakers. I asked that question back in July.
 
I don't see why it would be considered 3rd world. We don't have the luxury of ordering a whole new switchgear, and I think that inspecting and trying to repair is better than doing nothing. 3rd world would be filling it with roofing tar, and wrapping it with 33. How would you fix this problem, if replacement wasn't an option?

 
I would get the GE service group to do it or retrofit to vacuum.. I have to wonder how your company can stay in business if they have do self repair on 40 year old switchear. Seems some kind of QA/QC, safety rewiew is needed. would hate to be standing next to it when energised. I have seem some nasty results in the past.
 
xxjohnh,

Read the original posts. He is just trying to fix his existing switchgear. What he is doing is done all the time. He wants to do it right and deserves credit for trying to do so. Thats why he posted here in the first place. Many of my clients have 40 year old (some older) switchgear and would rather have it then what is available today regardless of price. It is their choice after all.

It's easy to recommend replacing something with new when its not your money. Even I can do that.
 
They sure don't make them like they used to, thats for sure. Those magneblasts were the worst thing GE ever built of you ask thier accountants, dang things have lasted 50 years (or more) and could last 50 more.
 
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