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ekstra   ara
 Post subject: Utility Information
PostPosted: Mon Aug 25, 2014 6:27 am 

Joined: Mon Aug 25, 2014 6:24 am
Posts: 6
I'm attempting to get utility data for a project in China and, as you can imagine, it's been difficult - and not just because of the language barrier. They are saying they do not have single line to ground fault data or SLG X/R ratio because there is no ground. Is this true? I thought the utility always carried a ground and would know what it's 1ph fault contribution would be.


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 Post subject: Re: Utility Information
PostPosted: Mon Aug 25, 2014 7:52 am 
Sparks Level

Joined: Thu Jul 07, 2011 6:03 am
Posts: 64
Location: Netherlands
Why couldn't it be ungrounded? Where I live a lot of medium voltage distribution systems are ungrounded, although it's being phased out for HRG.

For your model simply enter 0 MVA as line to ground contribution, your calculation will simply use the ungrounded constant for incident energy (at least SKM does). If I can't get utility data I typically use ungrounded as an assumption since it's the worst-case and has no influence on the low voltage calculations, the impact of MV grounding is not that big on arc flash results.


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