OHSA’s new requirements indicate an evaluation of both single phase to ground faults and three phase faults should be performed above 15kV. For transmission stations (115kV and above), what criteria are you using to select the arc gap for three phase faults.
I initially was going to employee the spacing between the phase bushings (transformer, breaker,…), although the phase spacing between the bus conductors (or bus bar) would be the largest phase to phase spacing. What are everyone’s thoughts on this topic?
Thanks
Dan

If you are using ArcPro to do the analysis, then you don't need the gap spacing for three phase. In ArcPro, 3 phase open air arcs are derived by using a multiplier on the single phase result. This is acceptable to OSHA (see footnote 4 to Table 3 in Appendix E 1910.269)

The question really becomes what do you use for an arc gap for single phase? I have seen the insulator on a gang operated switch used as the gap and I have also seen the insulator height plus 15% used.

Thank you for the reply. I planned on calling Kinectrics to discuss the application of the multipliers. When reading through the work EPRI did, I interpreted the multiplier as an adjustment to account for the fact that there is more than one arc but I could be completely off.

The Help Section has the multipliers in it, Section 9.0 of ArcPro manual states about the multiplier. Please report back on your discussion with ArcPro. I have had some difficulties with emailing questions and getting timely responses.

Also what are you using for your Arc Gap distance?

I discussed the multipliers for a three phase fault with Kinectrics. When evaluating a three phase fault the three phase arcing current, arc duration associated with that arcing current, and the arc gap associated with that arcing current should be entered into Arcpro then the multiplier should be applied. He mentioned it is important to note that updated multipliers are included in the latest version of Arcpro.

At this point I think for single phase to ground faults we will continue to utilize the arc gaps provided by NESC and OSHA, although this is still under discussion.

So just to clarify:
Kinectrics said to use the 3 phase values and then the multiplier???

This goes counter to their published information with the latest version of ArcPro. In the manual it specifically states that the single phase incident arc energies are multiplied by a factor. Also the Help section of the software states that the single phase arc energy may be adjusted by the following factors with the multipliers listed.

The below statement is from Stephen Cress, one of the developers of ArcPro, in a email to me dated 4/17/14, which seems to still indicate that the single phase value is what is multiplied.



I would be interested to see from Kinectrics the statement about using the 3 phase values as inputs and then apply the multiplier.

Where exactly is this indicated?



Which version is latest? I'm still hoping for a version that will run on a 64 bit machine, but Kinectrics has ignored my emails.

OSHA requires the employer to make a reasonable estimate of the incident energy to which an employee would be exposed. There is no limit on the voltage level. There is a table in Appendix E which lists what methods OSHA would consider reasonable and the table headings are 600V and less, 601 V to 15kV and More than 15kV. One has to decide about SLG or 3 phase exposures.



I see you have the same issue I have with Kinectrics on their responses to emails. I have put tracers on the emails and know they are received, read but rarely replied to. Customer Service and after purchase support is not the best, IMHO. One would think with OSHA prominently mentioning ArcPro they would have a new version to run on a 64bit machine. Running XP Virtual is clunky!!