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| 3 phase overhead distribution line; single phase arc flash? https://brainfiller.com/arcflashforum/viewtopic.php?f=2&t=5538 |
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| Author: | arkanos [ Thu Jan 13, 2022 8:20 am ] |
| Post subject: | 3 phase overhead distribution line; single phase arc flash? |
OSHA 1910 Appendix E Table 3 permits single phase arc flash calculations if it can be demonstrated that multiple phases are separated sufficiently. In the case of 15kV+ arc flash studies, ARCPRO is permitted for single phase arc flash studies without having to use a multiplier/conversion factor. When you put these two together, how does one justify that a 3phase overhead 15kV+ line would likely only result in a single phase arc flash? Is the innate conductor spacing sufficient for this? |
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| Author: | Jim Phillips (brainfiller) [ Mon Jan 17, 2022 9:12 am ] |
| Post subject: | Re: 3 phase overhead distribution line; single phase arc fla |
For distribution and transmission lines, the spacing between phases is considered too great for an arc to initiate. Good question! |
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| Author: | stevenal [ Tue Jan 18, 2022 8:36 am ] |
| Post subject: | Re: 3 phase overhead distribution line; single phase arc fla |
I understood the new rules were intended to encourage covering the unworked phases. |
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| Author: | gsheetrock [ Mon Jan 24, 2022 10:15 am ] |
| Post subject: | Re: 3 phase overhead distribution line; single phase arc fla |
arkanos wrote: OSHA 1910 Appendix E Table 3 permits single phase arc flash calculations if it can be demonstrated that multiple phases are separated sufficiently. In the case of 15kV+ arc flash studies, ARCPRO is permitted for single phase arc flash studies without having to use a multiplier/conversion factor. When you put these two together, how does one justify that a 3phase overhead 15kV+ line would likely only result in a single phase arc flash? Is the innate conductor spacing sufficient for this? Some make the assumption that if coverups "blankets" are used on the other 2 hot phases, then a 1ph arc will occur. With coverups not used, it is possible multiphase arcs can occur on oh distribution. I suggest reading EPRI Papers, they have tested many real-world utility equipment for scenarios such as this, arcs up to 10 inches and greater may occur on oh distribution. Furthermore, the 2-inch gaps used by ArcPro are much too short for real-world conditions, so you may want to beware of OSHA's Tables that reflect a short, 2inch arc at 15-25kV. EPRI's lab testing energy results differ quite significantly from industry standards. I believe a new Table may be provided in the next NESC that depicts EPRI's testing results for utility Pad mounted Switchgear and Transformers. Energies 2-3 times larger than what is seen in IEEE Standards resulted from testing on real-world utility equipment. Evidently, NESC subcommittee decided to side with EPRI's results for creation of this new Table for Padmounted equipment and Transformers from 1-35 kV. So do you use NESC tables for padmounted equipment and Switchgear over 1kV, IEEE1584-2018 Standard, or suggested OSHA multipliers to apply to Table 410-2 of the NESC? Good luck with your decision making. Search for these EPRI papers on IEEE Scholar site: "Medium-Voltage Arc Flash in Open Air and Padmounted Equipment" "Comparison of IEEE 1584-2018 Predictions with Tests on Real-World Equipment" "Medium-Voltage Arc Flash in Switchgear and Live-Front Transformers" Greg Shirek |
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| Author: | DavidChief [ Mon Jan 31, 2022 11:28 am ] |
| Post subject: | Re: 3 phase overhead distribution line; single phase arc fla |
A bit off topic, but we have regular incidents (0 to 3 per year) where the wingspan of crows flying through the space between phases on a 24kV overhead feed are sufficient to initiate an arc that takes out the utility fuses. |
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