Abstract
Arc flash hazard prediction methods have become more sophisticated because the knowledge about arc flash phenomenon has advanced since the publication of IEEE Std. 1584-2002. The IEEE Std. 1584-2018 has added parameters for more accurate arc flash incident energy (IE), arcing current, and protection boundary estimation. The parameters in the updated estimation models include electrode configuration, open circuit voltage, bolted fault current, arc duration, gap width, working distance, and enclosure dimension. The sensitivity and effect changes of other parameters have been discussed in the previous literatures. This article explains the fundamental theory on the selection of electrode configurations and performs sensitivity analysis of the enclosure dimension that have been introduced in the IEEE Std. 1584-2018. According to the newly published model for IE estimation, the IE between vertical conductors inside a metal box (VCB) and horizontal conductors inside a metal box (HCB) can differ by a factor of two with other parameter constants. Using HCB as the worst-case scenario to determine the personal protection requirements may not be the best practice in all circumstances. This article provides guidance for electrode configuration selection and a sensitivity analysis for determining a reasonable engineering margin when actual dimension is not available.
Highlights
A N ELECTRIC arc is formed when two physically separated and energized conducting bodies transfer charge through air [21].Manuscript received February 27, 2020; accepted July 3, 2020
This section discusses the importance of using the exact enclosure dimensions and electrode configuration for incident energy (IE) calculation
The IE is calculated for the following range of values: 1) gap width: 1 in; 2) working distance: 18 in; 3) arc duration: 250 ms; 4) voltages: 0.48, 2.7, and 14.3 kV; 5) bolted fault current: 1, 50, and 100 kA for 0.48 kV and 1, 30, and 60 kA for both 2.7 and 14.3 kV; 6) electrode configurations: vertical conductors inside a metal box (VCB), VCBB, and horizontal conductors inside a metal box (HCB); 7) enclosure dimensions: 20 in × 20 in × 20 in to 49 in × 49 in × 49 in
Summary
A N ELECTRIC arc is formed when two physically separated and energized conducting bodies transfer charge through air [21]. The current flowing ionizes the air between the conductors, while converting it into plasma and causing a rapid increase in temperature. The glow to arc transition starts with the “dark discharge” [5] or Townsend discharge [13], where electric field accelerated free electrons collide with gas molecules and as a result free more electrons; this causes an exponential increase in current versus voltage, due to the rapid ionization of air. Incident energy (IE) is used to quantify the energy incident on the surfaces, equipment, or human, near the arc flash It is the area under the curve of the rate of heat transfer to a certain working distance, over time. Previous literatures [2], [8], [9], [11], [12], [15], have discussed sensitivity and effect of changes of other parameters besides the electrode configuration and enclosure dimensions
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