SCGEng1 wrote:
We have been discussing the following…evaluating remote racking as “open air†verses “in a boxâ€.
We have several locations where remote racking is being used both on LV and MV breakers. The control cable is typically 20-30ft. The switchgear (metal clad) is remote racked either doors closed or open. The operator stands at some off angle (not directly in front) with respect to the switchgear. Adjusting the working distance, in the IEEE 1584 equations, to the control cable length is still producing incident energy values higher then we believe are truly possible at these distances. We would like to see some actual test data, video, or other evidence for this situation. If anyone knows of any please let me know. The test videos we have seen, with the doors closed, do not show a fire ball rolling out 20 or 30 feet. We have experimented with using the “open air†calculation at these distances, as expected the results are more favorable. Our thought is the arc blast will begin to spread out after leaving the box. It should being to dissipate in all directions after some distance due to it is no longer being directed and channeled by the enclosure. In addition, we think the breaker mass, enclosure, and door, even thought not arc rated, will provide some attenuation as compared to an open box with visibly exposed bus. Comments?
Be very cautious with your assumptions, having lower Ei's won't be "favorable" to the person not wearing suffecient PPE.
IEEE is doing some more testing and research I nelieve in this area so we will need to wait for those results. While I agree with your thinking until a good model exists you are stuck with the calculations available.
But I can tell you another utility recently had an arc flash event on 15kV switchgear and the fireball enguled the whole room, operators are convinced they would have been injured or worse if they had been anywhere in that room. Lucky for them they were racking the breaker in with a wireless remote racking unit.
It seems to me the best solution is to get a longer cable or go wireless.
