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 Post subject: Ground Relay Clearing Times for Arc Flash Calcs on O/H Lines
PostPosted: Tue Sep 02, 2014 12:05 pm 
Sparks Level

Joined: Sat May 17, 2008 5:00 pm
Posts: 85
Hi Everyone, I know IEEE 1584 assumes the arc flash is three phase or will balloon to three phase but on overhead transmission and distribution lines, I think most of us agree the arc flash isn't likely to jump many feet to the adjacent line. That being said, it makes sense that the lower of the ground relay or phase relay clearing time should be used. Does this make sense or am I missing something.

Also, do most people model the beginning and end of the line since the fault current can change significantly? Does anyone model it in some increment i.e. every mile or something. That sounds painful.
Thanks!


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 Post subject: Re: Ground Relay Clearing Times for Arc Flash Calcs on O/H L
PostPosted: Wed Sep 03, 2014 4:55 am 
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Joined: Wed May 07, 2008 5:00 pm
Posts: 822
Location: Rutland, VT
For overhead lines, ArcPro is used to model single phase, vertical, line to ground faults. This is the method that OSHA would fine acceptable to provide a reasonable estimate of incident energy on overhead lines.

The inputs to ArcPro are: SLG current, clearing time, arc gap, distance to arc gap and voltage. So, the clearing time for the SLG fault is used and lowering the clearing time will have an impact on the incident energy.

I model overhead distribution systems as follows:
1. Start of 3 phase backbone circuit
2. Halfway on 3 phase backbone circuit
3. End of 3 phase backbone circuit
4. End of longest single phase lateral circuit.

I think that would provide a reasonable estimate of incident energy on that circuit.

For transmission lines I would look halfway and calculate incident energy with the substations at either end supplying fault current and then each substation only providing fault current.


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