Arc flash happens when current passes between two separated electrodes through air, and it can occur in any electrical installation. Arc is a heat source that can lead to fire and explosions.
Switchboards are a key element for the protection and reliability of the power supply, and their design must be tailor-made for each system. The protection devices that connect the switchboard to the end loads must be carefully rated to achieve protection, coordination and selectivity.
The relation between personal safety and switchboard design can be measured in terms of the thermal incident energy that a worker is exposed to when near electrical installations. The way that a switchboard is designed and the protection device is set, have a direct impact on the incident energy. Thus, nine cases were simulated using ETAP software for three different electrode configurations, with reduced enclosure dimensions, shorter gaps between electrodes and different fault clearance times. The calculation methods are based on IEEE 1584 2018 .
The main findings were that arranging the electrodes vertically reached the lowest incident energy levels while the horizontal configuration the highest. Moreover, the longer it takes to clear the fault, the more the incident energy increases.
Furthermore, the case study was assumed to be located where a flammable gas was likely to occur during normal operation. Thus, the base case results were re-evaluated to verify if the heat generated was enough to auto-ignite the H2S if in sufficient concentration in the air.
The result was that the temperature reached way above the H2S minimum ignition temperature at closest to the arc source. Therefore, the switchboard must be tested and certified for use in explosive atmospheres to ensure that the energy transferred outside the enclosure is not sufficient to ignite a fire or an explosion.