Arc Flash Risk Assessment
What is an Arc Fault?
“An arc fault is a high-power discharge of electricity between two or more conductors. This discharge generates heat, which can break down a conductor's insulation and trigger an electrical fire. Arc faults can range in current from a few amps up to thousands of amps and are highly variable in strength and duration.”
Arc flash temperatures can reach or exceed 35,000 °F (19,400 °C) at the arc terminals. The surface temperature of the Sun is approximately 10,000 °F (5,600 °C)in comparison. The massive energy released in the fault rapidly vaporizes the metal conductors involved, blasting molten metal and expanding plasma outward with extraordinary force. During the arc flash, electrical energy vaporizes the metal, which changes from solid state to gas vapor, expanding it with explosive force. For example, when copper vaporizes it suddenly expands by a factor of 67,000 in volume.
The energy released in an arc flash incident, in a single phase-to-phase fault on a 480 V system with 20,000 (20kA) amps of fault current, the resulting power is 9.6 MW. If the fault lasts for 10 cycles at 50 Hz, the resulting energy would be 1.6 megajoules. For comparison, TNT releases 2175 J/g or more when detonated (a conventional value of 4,184 J/g is used for TNT equivalent). Thus, this fault energy is equivalent to 380 grams (approximately 0.8 pounds) of TNT.
Arc Flash Risk Assessment
VIR Consultancy has software tools to be able to comprehensively model any electrical power network to IEEE 1584-2018 (Standard on Arc Flash Studies) by applying simulated Phase to Phase and or Phase to Ground fault conditions. From the model we are then able to calculate the incident energy values (cal/cm2) and arc flash boundaries to determine the level of risk surrounding the electrical assets under evaluation.
From the data we are able to generate an Arc Flash Risk Report that determines risk, the severity (consequence) and the likelihood, as a means to be able to provide "reasonably practicable" recommendations around Arc Flash Mitigation that uses a combination of the Hierarchy of Arc Safety Controls in balance with a business's/clients level of acceptable risk and apply the selected safety controls back into the model to determine the residual risk in the system.
Did you know?
Under AS/NZS 61439 Low-voltage Switchgear and Control Gear Assemblies, arc fault containment and mitigation strategies are an optional specification, covered under AS/NZS 61439 Annex ZD that also references optional IEC TR 61641. The IEC arc fault containment test requirements are more descriptive and robust giving a higher level of safety protection.
In reference to the hierarchy of arc safety controls
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