Is a second disconnect really required?
Is a second disconnect really required?
(OP)
I came across this in an engineering book on substation design, and I have to admit I do not see the purpose, but the book seems to indicate that 4 disconnects per bay are required for a single breaker, double bus substation. My understanding is that only 3 disconnects are needed per bay, as the disconnect between the substation breaker and other two bus (selection) disconnects ends up being purely redundant.
However because the book is based with IEEE/ANSI systems in mind, I am lead to think that the other knows something that I do not (ie, NESC requirement).
However because the book is based with IEEE/ANSI systems in mind, I am lead to think that the other knows something that I do not (ie, NESC requirement).






RE: Is a second disconnect really required?
RE: Is a second disconnect really required?
RE: Is a second disconnect really required?
Although I think I am starting to see your line of thought in terms of gas partitions and increasing availability in GIS.
http://sites.ieee.org/houston/files/2016/02/8-GIS-...
RE: Is a second disconnect really required?
RE: Is a second disconnect really required?
Most of our substation outages require more than two isolation points. In our stations, we typically use both bus disconnects as the isolation points rather the bus side breaker as the isolation point.
RE: Is a second disconnect really required?
@Bacon4life: you are on to something. That might be a reason, but can't seem to find anything. What design are your substations?
RE: Is a second disconnect really required?
The protection issues with running allowing terminals to switch busses have been challenging enough that we just run it like a main and transfer scheme. The breaker bypass has become less important as we have moved to SF6 breakers which require fewer and shorter maintenance outages as well as can be replaced much faster than oil breakers.
RE: Is a second disconnect really required?
https://www.researchgate.net/profile/Jorge_Cardena...
Its possible the author had a SBDB with bypass in mind, but failed to include the bypass in his diagram. Other than that he knows something... is it possible the strain wire from the bus to breaker gantry could become live if it falls onto the bus bars?