Arc flash research findings presented at PCIC

“Effect of Insulating Barriers in Arc Flash Testing” is the title of a paper that circuit protection company Ferraz Shawmut presented at the IEEE PCIC, the annual technical conference of the IEEE’s Petroleum and Chemical Industry Committee, in Philadelphia.

The paper documents the company’s research findings regarding low-voltage arc flash testing using the standard IEEE 1584 test procedure, but with the electrode tips terminated in an insulating barrier instead of in the open air. This configuration is believed to be more representative of equipment in low-voltage industrial control panels and MCCs.

The paper, authored by R. Wilkins, M. Allison and M. Lang, describes arcing fault testing done in a high-power test laboratory with vertical conductors in a box, with the electrodes terminating in an insulating barrier. Testing components such as power distribution blocks, fuse holders and circuit breakers with the line-side arcing faults was compared to that of the barrier test. The insulating material, a solid 200-mm x 27-mm x 51-mm block of glass-reinforced melamine, was selected for its ability to withstand high electromagnetic forces. High-speed video documented the differences in arc development with and without the barrier.

Highlights of the research include:

• With the barrier in place, the arc’s downward development was redirected along the plane of the barrier, therefore, the high energy plasma flow went outward, toward the worker’s expected location
• Similar results could be observed when terminating vertical conductors in real industrial components
• Tests yielded energy density measurements nearly twice those predicted by the IEEE 1584 equations when measured with copper calorimeters 18 inches from the electrode tips. They also produced shorter arc lengths, higher arcing currents and higher maximum incident energy density when compared with the standard arrangement
• When the arcing fault was cleared by current-limiting fuses within the current-limiting range, there was no significant difference in energy density measurements compared to vertical testing
• Arcing faults are more likely to be imbalanced on LV systems in today’s power systems. This will require improved arc fault current prediction models
• Arcing faults were easily sustained at 208V for available fault currents as low as 4.2 kA
• The effect of the barrier and the source X/R on arc sustainability was also studied
• Vaporization of the copper electrode material was up to 60% higher than with other test configurations. High erosion of the copper electrodes directed a much larger quantity of copper spray toward the outside of the box
• Combined with the pyrolysis of the insulating material, it is likely that this configuration creates more toxic smoke under similar electrical conditions.

As a result of this research, Ferraz Shawmut recommends that the barrier test be a consideration in the current standard vertical test arrangement. This would be in addition to a horizontal arrangement with open electrode tips pointing at the calorimeters. Based on the findings, adding an insulating barrier to the standard test set-up could be more advantageous, since the barrier allows sustained arcing at 208V. Ferraz Shawmut proposed that a similar arrangement be incorporated into future revisions of the IEEE 1584 testing standard.
Click here to view the PDF on Effect of Insulating Barriers in Arc Flash Testing.