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 Post subject: Racking in medium voltage breakers - does this exist?
PostPosted: Tue Aug 02, 2016 6:56 am 
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Joined: Fri Jul 08, 2016 10:01 am
Posts: 227
Location: Indiana
The question of the week on racking in medium voltage breakers got me thinking about this video:

and what else could be done to prevent it from happening again. Yes, I know the guy was wearing insufficient PPE and should have had the door closed. I also know that in our newer gear where I work we have remote remote racking operators, fiber optic flash detection and tripping and the gear is designed differently to contain or re-direct an arcing fault.

All that said, I expect events like this mostly occur while racking the breakers in and out. What if there was a quick connect gas hose port in each cubicle with a nozzle inside to flood the stabs with SF6 or some other gas while racking? If there were a fault the gas should help knock it way down I would think and help to save the equipment even if you were using remote racking.

Maybe it already exists and I'm not aware or maybe it's not feasible due to not being enclosed would keep you from achieving a high enough concentration of gas, or the EPA wouldn't like it, or it would be too expensive. It is just a thought I had if there are any manufacturers reading this.

I also thought about compressed bottled gasses inside the gear with quick acting firing could possible serve a similar function but those would likely never fire fast enough and never be tested or maintained.

SKM jockey for hire

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 Post subject: Re: Racking in medium voltage breakers - does this exist?
PostPosted: Wed Aug 03, 2016 7:39 pm 
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Joined: Tue Oct 26, 2010 9:08 am
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Location: North Carolina
SF6 is about 100 times more potent than CO2 as a greenhouse gas. We can't waste it. The logical conclusion of your idea is if all the gear is in stainless enclosures and it is filled with SF6 (possibly under pressure) and welded shut. This is the GIS switchgear design. It is very expensive but has a 40 year service life and extremely little required maintenance. There is no way to rack anything.

A considerably less expensive option uses panel boards. You can't rack anything off the bus and failure rates are much less since about 75% of moving components are eliminated. There are research papers showing that rack mounted gear has little benefit in reality because it's cheaper to just include extra breakers.

At one time the choices were UL gear (panel boards) which is intentionally built with high duty rates because online maintenance is not possible. ANSI equipment is designed for low duty cycles and frequent maintenance. So panel board breakers are lubed for life (molded case or insulated case) but traditionally ANSI breakers are lubed at least every 3 years. So clearly ANSI gear is inherently higher risk if both receive adequate maintenance.

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