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 Post subject: Utility Breaker Clearing Time
PostPosted: Thu Jul 22, 2010 5:56 am 
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Joined: Tue May 18, 2010 7:03 am
Posts: 53
Just had to model my first job where there was no overcurrent protection at the utility pole. The station is close to the utility substation and the line is being protected by relays at the substation. The modeling software goes into specific detail in defining the breaker. What realistically do I need from the utility to model - # of cycle clearing time? Is there a standard for different voltage levels? If the breaker was part of my analysis I would need all the details but I don't want to be asking for info and having them jump through hoops for info I don't really need.

Thanks for your help.


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PostPosted: Thu Jul 22, 2010 8:35 am 
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Joined: Sun Dec 23, 2007 1:44 pm
Posts: 348
Location: Charlotte, NC
Source r+jx values, breaker rated interupting time, CT tap and OC relay settings, reclosing times, wire size and length, transformer %Z. Surprising that there is no high side protection unless it is a dedicated feeder to the plant.


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PostPosted: Fri Jul 23, 2010 6:52 am 
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Joined: Tue May 18, 2010 7:03 am
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The utility said there are only a few installations where there is no pole mounted protection. It only occurs when the station is very close to the substation - it's an old service.

I have pretty much everything you listed. How are the reclosing times used? The utility offered them and I see no mention of using them in the software. Thanks for any help.


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PostPosted: Fri Jul 23, 2010 9:02 am 
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Joined: Sun Dec 23, 2007 1:44 pm
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Location: Charlotte, NC
We usually try to make sure the breaker is on non-reclose when live maintenance is performed. Will be difficult in your case. The only issue is when/if one of your employees makes a mistake ahead of your OCPD. Many utilities operate distribution circuits with the first reclose cycle initiated as soon as the breaker opens.....no intentional time delay involved. Subsequent reclose cycles mey be as long as 10 to 30 seconds.

If you get an immediate reclose after the first trip of the utility breaker, the question is will the arc restrike?
Has the problem cleared?
Will the worker be clear?
Do we have a second event of some sort?

Is there a high side switch? You could always get the utility to kill it if you need to work on the main.

Hence my preference for the non-reclose.


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PostPosted: Tue Jul 27, 2010 5:46 am 
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Joined: Tue May 18, 2010 7:03 am
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Thank you for the explanation. This would definitely be an issue on the line side of the main service breaker for county personnel. The software doesn't account for it but it needs to be pointed out to the customer. Is that a true statement?


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PostPosted: Thu Aug 05, 2010 10:08 am 
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Joined: Sun Dec 23, 2007 1:44 pm
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Location: Charlotte, NC
Sorry for taking so long to get back....yes it does need to be pointed out and depending on the IE level you might want to make sure it is not worked energized.


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