Analysis of Asymmetrical Component Influence on Arc Current in the Determination of Arc Thermal Performance Value of Protective Personal Equipment

An evaluation of relevance of current asymmetry on arc flash tests intended to determine arc rating parameters on fabrics and garments, as well as face shields, gloves, and other materials were performed. Asymmetrical current is mentioned in American Standards (ASTM F 1959) to be maximum during tests and a reference on International Standard IEC 61482-1-1:2009, item 6.9, where an X/R ratio is required to obtain an asymmetry factor of 2.3, with a recommended source voltage of 2000 V. IEEE 1584 studies on the other hand states all calculation processes not clearly regarding asymmetry of fault current but assuming the linear effect of time and current on energy derived from steady-state current values. Technical basement for the asymmetry factor is never mentioned on arc flash test standards but it is supposed to be related to test strength conditions. As thermal conversion relationship with asymmetry is not clear in the literature, this study investigated, simulated, and performed practical measurements of electrical and thermal parameters related to arc flash tests, concluding that both symmetrical and asymmetrical arcing currents will confer the same arc rating results. Practical tests also showed that a source voltage of 2000 V is necessary only to produce arcing current asymmetry as lower voltages can be used to ignite and keep symmetrical arcing current for sufficient time on the arc rating tests, as previously regarded on literature which reduces significantly test setup and circuitry.