Folks,

Since PMHs have inter-phase barriers, chances of 3 phase bolted faults are pretty low (15kV rated system). What is your SOP for AF studies in this situation? I currently only have access to SKM (no ArcPro). Do you use the 3 phase calc's or calc using single phase values?

Thanks for the feedback,

Mike

I think you will find that the incident energy levels will be low based on phase separation distances and fault currents. One thing to consider is that since this is utility equipment and voltages, you should consult OSHA 1910.269 Appendix E for doing an arc flash assessment.

PMH-style switches can have high incident energies. EPRI and PG&E have tested a lot of these units. The barriers are good at preventing a phase-to-phase fault, but a fault can start as a single-phase fault and propagate to multiple phases. What happens is that the cabinet fills with hot gases. Those cause a flashover on a bus-support insulator on adjacent phases. This can take tens of cycles. We've also seen evidence of this from a unit from the field that was involved in an accident.

These switches also have high incident energies because they are an HCB configuration. In fact, test results show incident energies are up to 2X worse than the HCB model in IEEE 1584-2018.

For more information, see these papers:

* https://distributionhandbook.com/papers ... ission.pdf
* https://distributionhandbook.com/papers ... s_2021.pdf