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 Post subject: IEEE 1584, switchgear
PostPosted: Wed Aug 24, 2011 9:06 am 
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Could someone tell me if the switchgears are considered to have "open door" in IEEE 1584?


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PostPosted: Wed Aug 24, 2011 12:19 pm 
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IEEE 1584 assumes the switchgear is open. However, as posted in other threads on the forum, if the door is closed, there is no reduction in the available incident energy. (doors could blow off).

However, if the equipment is arc resistant, then even though there is a prospective incident energy of some value, it is assumed the doors remain closed and the energy is directed elsewhere.

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PostPosted: Thu Sep 08, 2011 5:16 pm 
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brainfiller wrote:
.......
However, if the equipment is arc resistant, then even though there is a prospective incident energy of some value, it is assumed the doors remain closed and the energy is directed elsewhere.


The caveat here is that per C37.20.7 the arc resistant rating is valid up to a predefined clearing time. We have purchased 38 kV arc resistant Switchgear with a 50 kA, 30 cycle rating. This means that my relaying scheme must be designed to clear the fault in less than 30 cycles for the arc resistant rating to be valid. For all intents and purposes this means that a main-tie-main MV lineup must have a bus differential. With just 51 and 51G relays it's not typically possible to coordinate between loads, feeder breakers, tie, and main and clear in under 30 cycles. The alternate that would be acceptable instead of bus differential is Zone Selective Interlocking - ZSI is a few cycles slower than bus diff, but still keeps you well under 30 cycles and doesn't require dedicated CTs.


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